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Background and aims: The intake of selenium, an essential element for animals and humans, in ruminants is largely determined by selenium concentration in ingested forages, which take up selenium mainly from soil. Ruminant excreta is a common source of organic fertilizer, which provides both nutrients and organic matter. This study aims to unentangle the unclear effect of applying different types of ruminant excreta in soils of different organic matter contents on selenium uptake by forage. Methods: Perennial ryegrass (Lolium perenne) was grown in soils of different organic matter contents. Urine and/or feces collected from sheep fed with organic or inorganic mineral supplements, including selenium, were applied to the soils. The selenium in the collected samples were analyzed using ICP-MS. The associated biogeochemical reactions were scrutinized by wet chemistry. Results: The application of urine and/or feces resulted in either the same or lower selenium concentrations in perennial ryegrass. The excreta type did not affect total selenium accumulation in grass grown in low organic matter soil, whereas in high organic matter soil, feces resulted in significantly lower total selenium accumulation than urine, which was attributed to a possible interaction of selenium sorption in soil and microbial reduction of Se. Conclusion: This one-time excreta application did not increase, but further decrease in some treatments, selenium concentration and accumulation in the perennial ryegrass. Consequently, to increase ruminant selenium intake, supplementing selenium directly to animals is more recommended than applying animal manure to soil, which might drive selenium reduction and decrease selenium uptake by grass. [ABSTRACT FROM AUTHOR]

Purpose: The incorporation of ryegrass (Lolium multiflorum Lam.; RG), a winter manure, could partly replace chemical N and reduce N loss during the succeeding rice seasons, but little is known about its impact on greenhouse gas emission. This study investigated the effect of different RG-urea substitution ratios (0% RG and 100% urea, 25% RG and 75% urea, 50% RG and 50% urea, 75% RG and 25% urea, 100% RG and 0% urea,) on net C and N mineralization, CH4 and N2O emissions in a paddy soil. Methods: Gas samples for CH4 and N2O fluxes were collected by using a closed chamber and determined by chromatograph method. Net C and N mineralization from the incorporated RG residue were tested by a mesh bag method. Results: Net C and N mineralization from RG followed a single exponential decay model, with 95.5%-97.8% of the original C and 98.7%-99.3% of N released during 192 days. The RG-urea substitution ratio increased CH4 emission, but was negatively correlated with N2O emission. In comparison with 0% substitution, global warming potential (GWP) and greenhouse gas intensity (GHGI) were not significantly different for the 25% and 50% RG substitutions, but were significantly higher for the 75% and 100% substitutions (P < 0.05). Soil redox, C and N remaining in litter residue were key characteristics explaining CH4 emission, while NH4+-N and NO3−-N were correlated with N2O emission. Conclusion: The increased GWP by CH4 emission after RG incorporation could be offset by N2O reduction when RG-urea substitution ratio was 50% or less. [ABSTRACT FROM AUTHOR]

Purpose : Nitrogen (N) transfer from white clover (Trifolium repens cv.) to ryegrass (Lolium perenne cv.) has the potential to meet ryegrass N requirements. This study aimed to quantify N transfer in a mixed pasture and investigate the influence of the microbial community and land management on N transfer. Methods: Split root 15N-labelling of clover quantified N transfer to ryegrass via exudation, microbial assimilation, decomposition, defoliation and soil biota. Incorporation into the microbial protein pool was determined using compound-specific 15N-stable isotope probing approaches. Results: N transfer to ryegrass and soil microbial protein in the model system was relatively small, with one-third arising from root exudation. N transfer to ryegrass increased with no microbial competition but soil microbes also increased N transfer via shoot decomposition. Addition of mycorrhizal fungi did not alter N transfer, due to the source-sink nature of this pathway, whilst weevil grazing on roots decreased microbial N transfer. N transfer was bidirectional, and comparable on a short-term scale. Conclusions: N transfer was low in a model young pasture established from soil from a permanent grassland with long-term N fertilisation. Root exudation and decomposition were major N transfer pathways. N transfer was influenced by soil biota (weevils, mycorrhizae) and land management (e.g. grazing). Previous land management and the role of the microbial community in N transfer must be considered when determining the potential for N transfer to ryegrass. [ABSTRACT FROM AUTHOR]

Aims: The aim of this work was to evaluate the fertilizing effect of three anaerobic co-digestates on the growth of the herbaceous plant Lolium rigidum. Methods: Nine treatments, combining different nutritional solutions (organic and inorganic) and number of fertilizations (one or two) were evaluated. Organic nutritive solution: plants grown with different olive mill solid waste (OMSW) -microalgae co-digestates: 75% OMSW-25% Raphidocelis subcapitata, volatile solids (VS) basis (OMSW-Rs); 50% OMSW- 50% Chlamydomonas Reinhardtii, VS basis (OMSW-Chl); and 75% OMSW-25% Secenedesmus quadricauda, VS basis (OMSW-Sq). Inorganic nutritive solution (INS): plants grown with inorganic Hoagland nutrient solution at 50%. After 60 days of experimentation, biometric and nutritional characteristics and photosynthetic activity were measured. Results: The results showed a favourable growth, development and nutritional quality of L. rigidum plants when digestates obtained from the anaerobic co-digestion of OMSW-microalgae are used as organic nutritional solutions as opposed to INS ones. The highest total biomass of L. rigidum was obtained with the treatments that involved two fertilizations. No inhibition due to excess nutrients was observed. A higher root/shoot ratio was achieved with the digestates of OMSW-Rs and OMSW-Ch as compared to that obtained with OMSW-Sq (F = 17.23 p ≤ 0.001). The nitrogen shoot biomass obtained after the organic treatments with the above-mentioned co-digestates was higher than that obtained after the inorganic treatment. Net photosynthesis rates did not present differences in the co-digestates treatments, being equal or superior to the INS treatments. Conclusions: The use of the anaerobic co-digestates from OMSW-microalgae can be considered a viable and promising alternative to inorganic fertilization. [ABSTRACT FROM AUTHOR]

Background and aims: Incorporation of biochar into the soil sequesters C for millennia, but the concomitant effects on plant rhizodepositions and nutrient (e.g., nitrogen; N) trade-offs via interactions of heterotrophic microbiota, might offset this sequestration. Methods: Ryegrass (Lolium perenne L.) with and without biochar amendment were pulse labelled in a 13CO2 atmosphere and 15N fertilizer added. Ryegrass and soils were destructively sampled at 16 and 30 days after seedling emergence. Isotope analysis was coupled with MiSeq sequencing of bacterial (16s rRNA) and fungal (ITS) genes to identify the effect of biochar on the associated microbiota involved in 13C allocation into soil aggregates and promotion of 15N uptake by L. perenne. Results: Biochar increased root biomass and 15N uptake but decreased rhizodeposited-13C recovery from large and small macroaggregates (by 12–57% and 57–72%, respectively). These changes in 13C flow and 15N uptake were accompanied by an increase in microbial biomass, and enhanced negative correlations between bacteria and fungi. O2PLS indicated members of seventeen genera that were correlated with soil stabilization of rhizodeposits in soil and plant N-uptake. For instance, Xanthomonadales (Proteobacteria) and RB41 (Acidobacteria), previously reported to be plant growth promoting rhizobacteria, were found to be positively correlated with 15N uptake by L. perenne. Conclusions: Our research explored the genera associated with biochar-modified 15N uptake by Lolium perenne and photosynthate 13C allocation into soil aggregates. Future research with SIP is required to fully assess microbial turnover, the ubiquity of similar rhizosphere microbiota and their fundamental importance for sequestration in the plant-soil-microbe-biochar systems. [ABSTRACT FROM AUTHOR]

Aims: An Italian ryegrass cultivar (Lolium multiflorum Lam. cv. Bb2067), selected and bred for increased leaf magnesium (Mg) concentration in the 1970s, reduced the incidence of hypomagnesaemia in sheep under experimental grazings. Here, we report evidence from archival experiments showing that cv. Bb2067 had consistently greater Mg concentrations at multiple sites. We also aimed to quantify variation in leaf Mg concentration among modern perennial ryegrass (Lolium perenne L.), hybrid ryegrass (Lolium perenne × multiflorum), and tall fescue (Festuca arundinacea Shreb.) cultivars. Methods: Data are reported from unpublished 1980s field-plot experiments for cv. Bb2067 and contemporaneous reference cultivars, sown at two UK locations in 1983 and 1984, and from 397 cultivars of modern forage grass in 13 UK-based breeding experiments sampled in spring 2013. Results: Across sites, years and cuts, cv. Bb2067 had a consistently greater leaf Mg concentration and lower potassium (K) concentration and forage tetany index (FTI) than reference cultivars in the 1980s experiments. Seasonal variation in leaf Mg and K concentrations and FTI were observed in the 1980s experiments, with K concentrations being generally greatest and Mg concentrations smallest in spring. Among modern forage grasses, there was large variation in leaf Mg concentration (up to 6.3-fold) and FTI (up to 2.1-fold), both within and between species, which varied independently of yield. Among a subset of hybrid ryegrass cultivars, there is evidence that the high Mg trait is already present in some modern breeding lines, albeit previously unreported. Conclusions: The variation in leaf Mg concentration and FTI among old and new cultivars shows there is considerable potential to breed forages with improved mineral quality to improve livestock health, potentially without compromising yield or other nutritional traits. [ABSTRACT FROM AUTHOR]

Background and aims: Interactions between functional groups of soil fauna and plants are poorly explored although they drive functional processes such as nutrient availability and therefore plant performance. Here, we investigated the separated and combined effects of two collembolan functional groups on soil properties and growth of Lolium perenne, a typical grass species from temperate grasslands. Methods: Under microcosm conditions, we established four treatments based on the presence and combination of two collembolan functional groups: (1) control without Collembola; (2) epedaphic species; (3) euedaphic species; (4) epedaphic + euedaphic species. After five months of experiment, we measured the effect of those treatments on both nutritional and morphological variables of L. perenne and on soil properties. Results: Collembolan presence stimulated plant performance. Individuals of L. perenne growing with euedaphic species presented higher numbers of leaves and nutrient contents compared with individuals growing with epedaphic species. Further, the combination of both collembolan functional groups enhanced plant performance and soil nutrient availability, demonstrating that a functionally diversified soil fauna assemblage cause overyielding of ecological processes. Conclusion: Our results provide evidences of complementarity interactions between different functional groups of soil fauna causing overyielding of primary production. [ABSTRACT FROM AUTHOR]

Background and aims: Low temperature stress is a common hazard during plant growth. Endophyte infection has been shown to increase cold tolerance in host plants. Many Lolium perenne cultivars contain low to moderate levels of endophyte. This study was done to explore cultivar improvement by segregation of endophyte containing individuals from the original cultivar to create a high endophyte subpopulation. Methods: Endophyte-infected plants were segregated over the first 3 years to produce high-endophyte subpopulation, and field and greenhouse experiments were carried out in the forth and fifth to determine the cold tolerance of the L. perenne subpopulation with high endophyte infection rates (N), the parent (F), the control endophyte-free subpopulation (E) and the control local variety (L). Results: (1) After 3 years of screening, high endophyte infection rates in the tillers and seeds of plants were still observed (96.5%), and agronomic traits (crown width, plant height, panicle number, withering, regreen-up, the growth cycle and the over-wintering rate) was also improved with increased Epichloë colonization of host plant. (2) The subpopulation with high endophyte infection rates and improved agronomic traits had better cold tolerance than the parent, the control endophyte-free subpopulation and the control local variety. The possible mechanisms by which high endophyte infection enhances cold resistance in the field include increased root system, increased the over-wintering rate, reduced regrowth periods with the sowing date being October 15th. (3) The high-endophyte subpopulation significantly increased SOD, POD, CAT, and APX activities at 0, 5, and 10 °C by 11.8%–44.6%, compared with the parent population. Conclusions: The subpopulation had a high endophyte infection rate, improved agronomic traits and higher enzymatic activities. These results indicate that increasing endophyte infection rates by selection, effectively improved agronomic traits and cold tolerance. [ABSTRACT FROM AUTHOR]

Aims: Deep-rooted agricultural crops can potentially utilize deep soil moisture to reduce periods where growth is water limited. Chicory (Cichorium intybus L.) is a deep-rooted species, but the benefits of deep roots to water uptake has not been studied. The aim of this study was to investigate the value of deep roots (>2 m) under topsoil water limitation. Methods: Chicory grown in 4 m deep soil-filled rhizotrons was exposed to either topsoil drought or resource competition from the shallow-rooted species ryegrass (Lolium perenne L.) and black medic (Medicago lupulina L.). The effect on deep water uptake was assessed using non-destructive measurements of roots, soil water and tracers. Results: Water uptake occurred below 1.7 m depth in 2016, and below 2.3 m depth in 2017 and contributed significantly to chicory water use. However, neither surface soil drying nor intercropping increased deep water uptake to relieve water deficit in the shoots. Conclusion: Chicory benefits from deep-roots during drought events, as it acceses deep soil moisture unavailable to more shallow rooted species, yet deep water uptake was unable to compensate for the reduced topsoil water uptake due to soil drying or crop competition. [ABSTRACT FROM AUTHOR]

Aims: We tested if chicory acquires nutrients from soil layers down to 3.5 m depth and whether the deep nutrient uptake increases as a result of drought or intercropping with ryegrass and black medic. We also tested whether application of the trace elements Cs, Li, Rb, Sr and Se, as tracers, result in similar uptake rates. Methods: The methodological tests were carried out in a pilot experiment where the tracers were applied to 1 m depth in lucerne and red beet grown in tube rhizotrons. The dynamics of deep nutrient uptake in chicory was studied in large 4 m deep rhizoboxes. A drought was induced when roots had reached around 2 m depth. Results: Chicory acquired 15N from 3.5 m depth and trace element tracers from 2.3 m depth. We found no compensatory tracer uptake with depth during drought. We found some indications of a compensatory tracer uptake from 2.3 and 2.9 m depth in intercropped chicory. Application of equimolar amounts of trace elements resulted in similar excess tracer concentrations within species. Conclusion: Chicory demonstrates nutrient uptake from below 3 m but does not increase deep nutrient uptake as a response to limited topsoil nutrient availability induced by drought or intercropping. [ABSTRACT FROM AUTHOR]

Aims: Roots are vital organs for plants, but the assessment of root traits is difficult, particularly in deep soil layers under natural field conditions. A popular technique to investigate root growth under field or semi-field conditions is the use of minirhizotrons. However, the subsequent manual quantification process is time-consuming and prone to error. Methods: We developed a multispectral minirhizotron imaging system and a subsequent image analysis strategy for automated root detection. Five wavelengths in the visible (VIS) and near-infrared (NIR) spectrum are used to enhance living roots by a multivariate grouping of pixels based on differences in reflectance; background noise is suppressed by a vesselness enhancement filter. The system was tested against manual analysis of grid intersections for both spring barley (Hordeum vulgare L.) and perennial ryegrass (Lolium perenne L.) cultivars at two time-points. The images of living roots were captured in wet subsoil conditions with dead roots present from a previous crop. Results: Under the soil conditions used in the study, NIR reflectance (940 nm), provided limited ability to separate between rhizosphere components, compared to reflectance in the violet and blue light spectrum (405 nm and 450 nm). Multivariate image analysis of the spectral data, combined with vesselness enhancement and thresholding allowed for automated detection of living roots. Automated image analysis largely replicated the root intensity found during manual grid intersect analysis of the same images. Although some misclassification occurred, caused by elongated structures of dew and chalkstone with similar reflectance pattern as living root, the system provided similar or in some cases improved detection of genotypic differences in the total root length within each tube. Conclusion: The multispectral imaging system allows for automated detection of living roots in minirhizotron studies. The system requires considerably less time than traditional manual recording using grid intersections. The flexible training strategy used for root segmentation offers hope for the transfer to other rhizosphere components and other soil types of interest. [ABSTRACT FROM AUTHOR]

Background and aims: Microbial denitrification is the primary driver of nitrogen losses from the plant-soil system and the key process for the closure of the global N cycle. All major controls of denitrification might be directly or indirectly affected by plants. However, there is a lack of research of the direct effects of plants on soil denitrification and how this effect might be mediated by soil properties. This study assesses the effect of three common crop species and two agricultural soils on denitrification potentials. Methods: We conducted a factorial experiment under controlled conditions to analyze the effects of (1) different plant species (barley, wheat or ryegrass), (2) two different soils (texture/ SOC) and (3) two different soil moisture levels on Denitrification Enzyme Activity (DEA) in bulk and rhizosphere soil. Results: The SOC richer clay loam soil showed on average higher DEA (+81%) compared to the SOC poorer silty loam soil. All three plants were found to stimulate denitrification with significant differences between certain species: rye grass (+92% ± 14%) ≥ barley (+75% ± 26%) ≥ wheat (+50% ± 19%). Conclusions: DEA in agricultural soils is interactively controlled by plant species and soil type with an overall stimulating effect of plants on the denitrification potential. Future research should focus on disentangling single mechanisms of plant control on actual denitrification rates and N gas product ratios. [ABSTRACT FROM AUTHOR]

Aims: Belowground legume nitrogen (N) composed of roots and rhizodeposition is an important N input to soils, but published data of belowground N vary broadly, probably due to extrapolation from short-term experiments and dissimilar growing conditions. We quantified belowground N inputs of red clover (Trifolium pratense L.) during two consecutive years in a clover-grass sward along a soil nutrient availability gradient.Methods: We established a red clover-perennial ryegrass (Lolium perenne L.) model sward in microplots located in field plots of the DOK experiment, which has a 33-year history of organic and conventional cropping, resulting in a soil nutrient availability gradient. Four treatments were examined: the zero fertilisation control, bio-organic with half and full dose manure application, and the conventional system with mineral fertilisation at full dose. We studied the development of clover aboveground and belowground N using multiple pulse 15N urea leaf labelling.Results: Belowground clover N increased over time and with rising nutrient availability and was proportional to aboveground clover N at all times. Belowground clover N amounted to 40% of aboveground clover N during two consecutive years, irrespective of the nutrient availability status. Belowground clover N development was initially dominated by fast root growth, followed by enhanced root turnover during the second year. Potassium availability limited clover growth and total N accumulation in treatments with low nutrient availability.Conclusions: Belowground red clover N inputs could be estimated from aboveground N by a constant factor of 0.4, regardless of the nutrient availability and cultivation time. Root turnover led to a distinct absolute increase of N rhizodeposition over time. Hence, N rhizodeposition, with an 80% share of belowground N, was the predominant N pool at the end of the second year. [ABSTRACT FROM AUTHOR]

Aims: To evaluate the efficiency of acidified (to pH 5.5) and dried digestate solids as a fertilization product in a pot experiment with ryegrass. Methods: The NH-N pool of the solids was labelled with N prior to acidification and drying to estimate plant N uptake efficiency. The effect of digestate solids on plant growth and N and P uptake was compared to the effect of different mineral N-P fertilization combinations. Results: Non-acidified dried digestate solids showed inferior N fertilization performance compared to their raw and acidified counterparts, and higher drying temperature reduced solids N mineralization. More than 40% of the NH-N in the raw, raw acidified and acidified dried solids treatments was recovered by the ryegrass over 5-months, similar to recovery with medium mineral N rates, resulting in mineral fertilizer equivalency of 32-41%. Digestate solids treatment altered the water extractable P of the solids, but less so the ryegrass P uptake, mainly due to the buffer capacity of the soil. However, ryegrass P uptake in non-acidified dried solids treatments was probably inhibited by poor growth due to low N availability. Conclusions: Acidification of digestate solids prior to drying may be an important treatment to maintain the solids fertilizing value while enhancing its manageability. [ABSTRACT FROM AUTHOR]

Background and aims: Nitrogen balances are useful tools to increase our understanding of soil N processes and the efficiency of plants in taking up animal urine-N. This study aimed to investigate the effect of forage type on the fate of autumn-applied urine-N (700 kg N ha). Methods: In a 17-month lysimeter study the recoveries of N in herbage, leachate, nitrous oxide, and soil + roots (at the end of the trial) were determined for three forage types: perennial ryegrass-white clover (RGWC, Lolium perenne L. -Trifolium repens L.), Italian ryegrass (Italian RG, Lolium multiflorum Lam.), and lucerne ( Medicago sativa L.) under simulated autumn grazing. Results: We recovered 81.5-85.5% of the N applied in the urine. Italian RG had the greatest amount of urine-N recovered in the herbage (49.5%) and the least recovered in leachate (16.8%) making it the most efficient of the three forages for utilizing urine-N. For RGWC, herbage and leachate recoveries were 40.1% and 23.7% , respectively. Lucerne was the least efficient with recoveries of N in herbage and leachate equaling 18.4% and 52.5%, respectively. Conclusions: This study demonstrates that Italian ryegrass could offer benefits in reducing urine-N leaching losses through its ability to take up more urine-N over winter. [ABSTRACT FROM AUTHOR]

Background and aims: There is substantial evidence that legume-derived Nitrogen (N) is transferred to neighboring non-legumes in grassland mixtures. However, there is sparse information about how deep rooted non-legume forage herbs (forbs) influence N transfer in multi-species grasslands. Methodology: Red clover ( Trifolium pretense L.) was grown together with perennial ryegrass ( Lolium perenne L.) and one of three forb species: chicory ( Cichorium intybus L.), ribwort plantain ( Plantago lanceolata L.) or caraway ( Carum carvi L.) in a field experiment. During the first year after the establishment, red clover leaves were labeled with N-urea to determine the N transfer from red clover to companion ryegrass and forbs. Results: On an annual basis, up to 15 % of red clover N was transferred to the companion ryegrass and forbs, but predominantly to the grass. The forb species did not differ in their ability to take up clover N, but biomass production and soil N acquisition was higher in chicory and plantain than in caraway. Conclusions: Grass relied to a great extent on clover N, whereas forbs relied on soil N. Soil N-enrichment indicated that N transfer occurred in the upper soil layers and that a dependence on clover-derived N did not necessarily give grass a growth advantage. [ABSTRACT FROM AUTHOR]

Aims: Increasing the input and turnover of root tissue is considered to be one method that may increase carbon (C) inputs and storage in soil. The use of herbicide during pasture renewal (periodic re-sowing of pasture) is expected to increase root inputs and turnover as plants die. The objective of this study was to quantify the short-term impact of pasture renewal on root turnover and C input to soil of ryegrass-clover pastures. Methods: Pastures were labelled in the field using a C isotope pulse labelling method within 1 m clear chambers. Five daily labelling events were carried out during one week in paired treatment plots within 3 replicate paddocks. One plot per paddock was sprayed with herbicide and then the pasture was renewed by direct drilling of seed. The C of roots and soil (0-100 mm) was measured at regular intervals over an 89-day period. Results: Herbicide application caused an initial rapid turnover time of 17 days followed by a slower turnover time of 524 days, compared to unsprayed pasture which had a root turnover of 585 days. Faster root turnover following herbicide application resulted in greater cumulative C input to soil over 89 days with approximately double the C input in the sprayed treatment (3238 ± 378 kg C ha) compared to the unsprayed treatment (1726 ± 540 kg C ha). Conclusions: The use of glyphosate during pasture renewal increased root turnover and resulted in a greater short term cumulative C input to soil. This study provides the first values of root turnover and C input to soil during a pasture renewal event in New Zealand pasture systems and contributes to the understanding of how pasture roots may influence the soil C input following plant death in grassland systems. [ABSTRACT FROM AUTHOR]

Aim: A principal goal of grassland management is to minimize the use of artificial fertilizers by maximising the productivity of nitrogen-fixing leguminous plants such as clovers. The objective of this study was to investigate whether a plant-growth-promoting strain of the free-living rhizosphere fungus Trichoderma hamatum (GD12) could be used as a natural and sustainable means of enhancing the competitiveness of white clover ( Trifolium repens) while allowing increased productivity of both clover and ryegrass ( Lolium perenne) in mixed species systems. Methods: An assay was conducted in rhizotrons with white clover and ryegrass sown alone and in mixture and in soils inoculated and non-inoculated with GD12. Plant height, growing rate, phenological stage, number of Rhizobium nodules and biomass were assessed. A histological study of Rhizobium nodules and a stable isotopes analysis was conducted to determine the N fixation capacity of white clover. Results: When introduced as a soil inoculant, the fungus increased biomass production of both plant species and shortened their phenological cycles. Furthermore, in clover, GD12 enhanced plant height and growth rate and stimulated Rhizobium nodulation, while N stable isotope analysis demonstrated increased N fixation. Conclusion: This shows that soil amendment with a beneficial strain of saprotrophic fungus bestows a competitive advantage to white clover in clover-ryegrass mixtures and provides a sustainable mechanism for improving the mixture productivity. [ABSTRACT FROM AUTHOR]

Background and aims: Plant uptake of active pharmaceutical ingredients (APIs) is increasingly leading to concerns about their potential exposure to humans and wildlife via dietary intake. Due to the extraordinary ability of biochars to bind organic compounds, plant uptake experiments were conducted to assess the effect of soil-amendment of three different biochars on the uptake of APIs from spiked soil. Methods: Pot experiments were undertaken to assess the extent of sorption and corresponding bioaccessibility of two APIs (carbamazepine - CBZ and propranolol -PRL) to ryegrass ( Lolium perenne) grown in an API-spiked loamy sand, with and without biochar amendment (5 t/ha equivalent). The soil was amended with three different biochars produced from eucalyptus wood and wheat residues. Results: Both APIs were taken up by ryegrass, with CBZ preferentially accumulated (14.3 mg/kg CBZ, 3.8 mg/kg PRL in unamended soil) due to its comparatively high concentration in porewater. Soil amendment with biochars increased partitioning of the two APIs by up to three- fold, with corresponding decreases in porewater (34-72 % of unamended soil) and plant tissue (17-64 %) concentrations. Conclusions: Biochars were effective in reducing the uptake of APIs into plant tissues from a contaminated soil and may be effective in the management of API residues in contaminated soils. [ABSTRACT FROM AUTHOR]

Background and aims: A strategy to increase soil C under pasture-based systems is to increase the root mass inputs or increase rooting depth of plants. Our objective in this study was to measure the seasonal dynamics of root mass and C inputs under two different pasture types (ryegrass-clover vs moderately diverse) that differ in plant diversity and which are commonly used in New Zealand agriculture. Methods: This study was carried out on an existing plant diversity field trial containing six replicate paddocks of both moderately-diverse and ryegrass-clover pastures. Soil cores (0-100-200-300 mm sections) were collected seasonally across 1 year and individual root traits assessed from all species. Results: The moderately diverse pasture had greater root mass (5320-9350 kg ha) than the ryegrass-clover pasture (3810-5700 kg ha) for all seasons and had greater root mass lower in the soil profile. A secondary objective demostrated no significant difference in root mass between high and low sugar ryegrass cultivar. Increased root mass results in an estimated increase of C input to the soil of about 1203 kg C ha (0-300 mm depth) under the moderately diverse pasture, excluding root exudates. Root trait measurements demonstrated a greater diversity of root traits in the moderately diverse sward compared to the ryegrass-clover pasture. Conclusions: Moderately diverse pasture systems offer scope to increase soil C under grazed pastures through increased root mass inputs and rooting depth. [ABSTRACT FROM AUTHOR]

Aims: The objectives of this study were to compare techniques for measuring biological nitrogen fixation (BNF) and to assess how fertiliser N input affects the balance between BNF and sustainable herbage production on perennial ryegrass ( Lolium perenne L.)/white clover ( Trifolium repens L.) grassland. Methods: Biological N fixation and herbage production by white clover based grassland was measured in 2011 and 2012 under four nominal annual fertiliser N inputs: 0 (0N), 86 (86N), 140 (140N) and 280 kg ha (280N). Biological N fixation was measured using the N isotope dilution and N natural abundance techniques under all fertiliser N inputs and also using the nitrogen difference technique under 0N. Results: The two N techniques produced similar annual estimates of above-ground BNF across the range of fertiliser N inputs. Fertiliser N input resulted in higher herbage dry matter yield, but reduced annual BNF which averaged 80, 64, 66 and 47 kg ha on 0N, 86N, 140N and 280N, respectively, across both techniques and years. Conclusions: The two N techniques were comparable in estimating BNF. Intermediate fertiliser N inputs achieved a balance between minimising detrimental impact on BNF and potential N loss while producing more herbage DM yield than clover swards receiving no fertiliser N. [ABSTRACT FROM AUTHOR]

Aims: The allelopathic activity of canola ( Brassica napus) germplasm was investigated using the important Australian weed, annual ryegrass ( Lolium rigidum) as the target species. Methods: Three different canola plant densities (10, 20, and 30 seedlings/beaker) of each of 70 world-wide genotypes were tested in vitro in close proximity to annual ryegrass seedlings. Results: The allelopathic activity of canola, as measured by reduction in annual ryegrass root and shoot growth, increased with canola crop seedling densities. Density did not consistently influence shoot length of annual ryegrass. Greater shoot length suppression was observed in genotype cv. Rivette and BLN3343CO0402. The Australian genotype cv. Av-opal and the breeding line Pak85388-502 suppressed root length of ryegrass more than other genotypes, even at low densities. At the lowest density, the least allelopathic genotypes were cv. Barossa and cv. Cescaljarni-repka, although they became more allelopathic at higher density. An overall inhibition index was calculated to rank each of the canola genotypes. There were significant differences between canola genotypes in their ability to inhibit root and shoot growth in ryegrass. Conclusion: Considerable genetic variation exists among canola genotypes for their allelopathic effects on annual ryegrass. Further investigation is required to determine the allelopathic mechanisms, particularly to identify the responsible allelochemical(s) and the gene(s) controlling the trait. This research suggests that highly allelopathic canola genotypes can be potential for controlling weeds such as annual ryegrass in integrated weed management programs. [ABSTRACT FROM AUTHOR]

Aims: Application of carbon (C) and nitrogen (N) isotopes is an essential tool to study C and N flows in plant-soil-microorganisms systems. When targeting single plants in a community the tracers need to be added via e.g., leaf-labeling or stem-feeding approaches. In this study we: (i) investigated if bicarbonate can be used to introduce C (or C) into white clover and ryegrass, and (ii) compared the patterns of C and N allocation in white clover and ryegrass to evaluate the homogeneity of tracer distribution after two alternative labeling approaches. Methods: Perennial ryegrass and white clover were pulse labeled with N urea via leaf-labeling and C either via a CO atm or with C bicarbonate through leaf-labeling. Plants were sampled 4 days after labeling and prepared for bulk isotope analysis and for C imaging to identify plant parts with high and low C activity. Subsequently, plant parts with high and low C activity were separated and analyzed for N enrichment. Results: Bicarbonate applied by leaf-labeling efficiently introduced C into both white clover and ryegrass, although the C activity in particular for white clover was found predominantly in the labeled leaf. Using C imaging for identification of areas with high (hotspots) and low C activity showed that C was incorporated very heterogeneously both when using bicarbonate and CO as expected when using pulse labeling. Subsequent analysis of N enrichment in plant parts with high and low C activity showed that N also had a heterogeneous distribution (up to two orders of magnitude). Conclusion: Bicarbonate can efficiently be used to introduce C or C into plant via the leaf-labeling method. Both C and N showed heterogeneous distribution in the plant, although the distribution of N was more even than that of C. [ABSTRACT FROM AUTHOR]

Backgrounds and aims: N rhizodeposition by legumes leads to enrichment of N in soils and in companion plants. N rhizodeposition can be divided into two major components, root exudation and root senescence. Our aim was to quantify N root exudation in white clover ( Trifolium repens L.) through an estimation of short-term N rhizodeposition and to assess its impact on N transfer to companion perennial ryegrass ( Lolium perenne L.) grown in mixture with clover. Method: N provided in the root atmosphere for 3 days was used to estimate transfer of symbiotically fixed nitrogen (SFN) to the growing medium by clover grown in pure stand and to ryegrass by clover grown in mixture for 2 months. Results: The proportion of N rhizodeposited over the 3 days increased from 3.5 % of SFN in pure stand to 5.3 % in mixture. The N-enrichment of ammonium from the adhering substrate shows that a part of the rhizodeposited N was released in the form of ammonium. 4 % of the rhizodeposited N was taken up by ryegrass during the labelling period. Conclusions: This study showed a significant contribution of root N exudation to the total N rhizodeposition of legumes and in the transfer of N to grasses. [ABSTRACT FROM AUTHOR]

Background and Aims: Below-ground translocated carbon (C) released as rhizodeposits is an important driver for microbial mobilization of nitrogen (N) for plants. We investigated how a limited substrate supply due to reduced photoassimilation alters the allocation of recently assimilated C in plant and soil pools under legume and non-legume species. Methods: A non-legume ( Lolium perenne) and a legume ( Medicago sativa) were labelled with N before the plants were clipped or shaded, and labelled twice with CO thereafter. Ten days after clipping and shading, the N and C in shoots, roots, soil, dissolved organic nitrogen (DON) and carbon (DOC) and in microbial biomass, as well as the C in soil CO were analyzed. Results: After clipping, about 50 % more C was allocated to regrowing shoots, resulting in a lower translocation to roots compared to the unclipped control. Clipping also reduced the total soil CO efflux under both species and the C recovery of soil CO under L. perenne. The N recovery increased in the shoots of M. sativa after clipping, because storage compounds were remobilized from the roots and/or the N uptake from the soil increased. After shading, the assimilated C was preferentially retained in the shoots of both species. This caused a decreased C recovery in the roots of M. sativa. Similarly, the total soil CO efflux under M. sativa decreased more than 50 % after shading. The N recovery in plant and soil pools showed that shading has no effect on the N uptake and N remobilization for L. perenne, but, the N recovery increased in the shoot of M. sativa. Conclusions: The experiment showed that the dominating effect on C and N allocation after clipping is the need of C and N for shoot regrowth, whereas the dominating effect after shading is the reduced substrate supply for growth and respiration. Only slight differences could be observed between L. perenne and M. sativa in the C and N distribution after clipping or shading. [ABSTRACT FROM AUTHOR]

Background: Soil to plant transfer models (SPT) are needed to predict levels of potentially toxic elements (PTE's) in crops in view of risk assessment. Methods: Here we developed a field study to test the suitability of empirical SPT models based on the reactive soil content in combination with soil properties versus a 0.01 M CaCl extraction to predict levels of metals and metalloids in ryegrass ( Lolium perenne). Results: Both empirical SPT models and the 0.01 M CaCl extraction explained between 14 and 68 % of the variation of Cd, Zn, Pb, Cu, Hg, As, Co and Ba in the ryegrass. Organic carbon and pH were the main variables explaining levels of elements in ryegrass. For Hg and Pb, amorphous aluminium oxides (Al) played a significant role. For B, Cr, Mo, Ni, Sb and U no significant relationship could be derived. Conclusions: Despite a range in the predictive quality of empirical SPT models reasonable to good estimates of As, Ba, Cd, Co, Cu, Hg, Pb and Zn in ryegrass could be obtained. The main advantage of SPT models is that they allow to account for differences in the availability of PTE's. Ultimately either SPT's or fixed crop levels can be the basis of a more realistic risk assessment framework addressing the transfer of contaminants from soil into the food chain [ABSTRACT FROM AUTHOR]

Background and aims: Aluminium (Al) toxicity limits pasture production in acidic soils, and there is evidence that antioxidant enzymes such as superoxide dismutase (SOD) play a key role against Al-induced oxidative stress. We have investigated (i) the relationship between Al-toxicity and oxidative damage as well as the time-course of SOD activity and (ii) the expression profiles of two SOD isoforms in the roots of two ryegrass cultivars. Methods: Jumbo (Al-sensitive) and Nui (Al-semi-tolerant) ryegrass cultivars were cultured hydroponically with 0 or 0.2 mM Al. Roots were colleted during 48 h to determine Al uptake, lipid peroxidation, SOD activity and the expression of LpCu/Zn-SOD and LpFe-SOD isolated genes. Results: LpCu/Zn-SOD and LpFe-SOD were classified phylogenetically as putative mitochondrial and plastidial SODs, respectively. Although Al accumulation did not differ between the two cultivars, lipid peroxidation increased 2.2-fold in Jumbo but only scarcely in Nui by the end of the time-course. An early response in terms of total SOD activity and differential expression of LpCu/Zn-SOD and LpFe-SOD genes occurred in both cultivars after Al treatment. Conclusions: SOD isoforms were up-regulated over a longer period in Nui compared with Jumbo, leading finally to a greater protection in roots against the short term Al-toxicity. [ABSTRACT FROM AUTHOR]

The contribution of below ground plant root tissue to soil carbon (C) pools is attracting considerable interest in the context of greenhouse gas mitigation options. A field experiment was conducted on a perennial ryegrass/white clover pasture in the Manawatu, New Zealand, to examine the effect of differing soil nitrogen (N) and phosphorus (P) fertility status on root dynamics. Root standing mass, shoot and root dry matter (DM) accumulation and root tissue decomposition were measured at 6-8 week intervals over one year at moderate (Olsen P = 24, no added N) and high (Olsen P = 49, 400 kgN hay added N) soil fertility levels. Shoot production was significantly greater in the high fertility treatment (2550 cf. 1890 gDM my) but differences in root dynamics were confined to two periods in spring and winter. In late spring the pattern was for lower root mass (183 cf. 231 gDM m between 0-80 mm depth) and higher root production (0.71 cf. 0.52 gDM m d between 0-120 mm depth) under higher fertility. In winter the reverse was observed. There is some evidence that the soil type used in the root in-growth cores underestimated root production values for this site by a factor of approx. one third. Short-term differences between the two fertiity treatments in standing root mass and root production did not lead to treatment differences in topsoil C and N changes over four years. This may reflect insufficient separation in the two soil fertility treatments and a low overall root tissue input to soil organic matter. [ABSTRACT FROM AUTHOR]

Grazing ruminants urinate and deposit N onto pastoral soils at rates up to 1,000 kg ha, with most of this deposited N present as urea. In urine patches, nitrous oxide (NO) emissions can increase markedly. Soil derived CO fluxes can also increase due to priming effects.While NO fluxes are affected by temperature, no studies have examined the interaction of pasture plants, urine and temperature on NO fluxes and the associated CO fluxes. We postulated the response of NO emissions to bovine urine application would be affected by plants and temperature. Dairy cattle urine was collected, labelled with N, and applied at 590 kg N ha to a sub-tropical soil,with and without pasture plants at 11°, 19°, and 23°C. Over the experimental period (28 days), 0.2% (11°C with plants) to 2.2% (23°C with plants) of the applied N was emitted as NO. At 11°C, plants had no effect on cumulative NO-N fluxes, whereas at 23°C, the presence of plants significantly increased the flux, suggesting plant-derived C supply affected the NO producing microbes. In contrast, a significant urine application effect on the cumulative CO flux was not affected by varying temperature from 11-23°C or by growing plants in the soil. This study has shown that plants and their responses to temperature affect NO emissions from ruminant urine deposition. The results have significant implications for forecasting and understanding the effect of elevated soil temperatures on NO emissions and CO fluxes from grazed pasture systems. [ABSTRACT FROM AUTHOR]

Soil NO emissions were monitored throughout a 3-year crop rotation including maize, fennel and a ryegrass-clover sward, at Borgo Cioffi NitroEurope site. NO emission rates were highly variable in time and space and controlled by soil nitrogen and soil water content. The NO effluxes were low for most of the monitored period. The highest NO emissions were recorded throughout the 2007 maize cropping season, ranged form 15.2 to 196.2 μg m h whereas the lowest ones ranged form −5 to 10 μg m h during the 2007-2008 ryegrass-clover winter crop. For the maize crops, NO peaks were detected after fertilization but with a delay of some weeks from applications, probably due to the presence of DMPP nitrification inhibitor in the applied fertilizer. A properly designed ANOVA model was developed to explain the influence of the main chemical-physical factors. This model also allowed the quantification of the delay time in peak emissions following fertilization, which resulted variable over the years and ranged between 2 and 21 days. A dependence of emissions from soil temperature and moisture was found, with significant interactions in some instances. Calculated Emission Factors (maize 2007: 0.48%; ryegrass-clover sward 2007-2008: 0.05%; maize 2008: 0.14%; fennel: 0.28% 2008-2009; maize 2009: 0.015%) resulted well below the values reported in the literature and the 1% reference value indicated by IPCC, probably due to a sub-optimal water regime inducing low Water Filled Pore Space (WFPS) values. [ABSTRACT FROM AUTHOR]

Plant species differ in their capacity to use nonexchangeable potassium (NEK) in soils. In this study two typical plants with high K use efficiency, ryegrass and grain amaranth, were compared with regard to their capacity to use K from five K-bearing minerals. Biomass relative yield and K uptake data indicated that ryegrass was much more efficient than grain amaranth at using NEK in minerals. Root exudates of grain amaranth collected under hydroponic culture contained considerable amounts of oxalic and citric acids, while these acids were not detected in ryegrass root exudates. Compared with grain amaranth, the kinetic parameters of K uptake by ryegrass roots were characterized by a significantly higher K uptake rate (V) and a significantly lower C, the minimum external K concentration at which K is taken up. The dynamic release of NEK from minerals in various solutions showed that the release rate of NEK was largely K-concentration dependent and some thresholds of K concentration prevented further NEK release from minerals. The K thresholds were related to mineral type and increased in the presence of Ca or Na in solutions. The positive effect of H (20 mmol L) on NEK release was also mainly attributed to elevating the thresholds of K concentration, rather than to the effects of weathering. The results indicated that the main mechanism by which plant species efficiently use NEK in minerals was to the capacity of plants to absorb K at low concentrations. The lower the C for the root K uptake, the higher the expected NEK use efficiency of the plant. [ABSTRACT FROM AUTHOR]

In Mediterranean countries, forage grasses and legumes are commonly grown in mixture because of their ability to increase herbage yield and quality compared with monocrop systems. However, the benefits of intercropping over a monocrop system are not always realized because the efficiency of a grass-legume mixture is strongly affected by agronomic factors. The present study evaluated productivity, N fixation, N transfer, and N recovery of berseem clover ( Trifolium alexandrinum) grown in pure stand and in mixture with annual ryegrass ( Lolium multiflorum) under high or low defoliation frequencies and varying plant arrangements (sowing in the same row or in alternating rows). On average, the berseem-ryegrass mixtures resulted in a greater yield and N yield than the monocrops. When mixed together, ryegrass was more efficient than berseem at absorbing soil N, increasing the reliance of berseem on N fixation. Both defoliation management and plant arrangement affected forage yield and the quality of the mixture, modifying the proportion of the two components, the N content of the forage, and the symbiotic N fixation of the legume. Reducing the proximity between plants of the two species may benefit the weaker component of the mixture. No apparent transfer of fixed N from berseem to ryegrass was detected. [ABSTRACT FROM AUTHOR]

Cool-season grasses commonly harbor fungal endophytes in their aerial tissues. However the effects of these symbionts on soil microbial communities have rarely been investigated. Our objective was to explore microbial community responses in soils conditioned by plants of the annual grass Lolium multiflorum with contrasting levels of infection with the endophyte Neotyphodium occultans. At the end of the host growing season, we estimated the functional capacity of soil microbial communities (via catabolic response profiles), the contribution of fungi and bacteria to soil activity (via selective inhibition with antibiotics), and the structure of both microbial communities by molecular analyses. Soil conditioning by highly infected plants affected soil catabolic profiles and tended to increase soil fungal activity. We detected a shift in bacterial community structure while no changes were observed for fungi. Soil responses became evident even without changes in host plant biomass or soil organic carbon or total nitrogen content, suggesting that the endophyte modified host rhizodepositions during the conditioning phase. Our results have implications for the understanding of the reciprocal interactions between above and belowground communities, suggesting that plant-soil feedbacks can be mediated by this symbiosis. [ABSTRACT FROM AUTHOR]

Soil-plant potassium (K) dynamics were studied using a long-term field experiment in order to evaluate the plant performance and K delivering capacity of the soil parent material. Rye grass ( Lolium perenne L.) based rotations on a loamy sand derived from granitic bedrock were studied over 30 years with two K-fertilisation regimes, nil (K0) and 65 kg K ha yr. Mineralogical and chemical methods were combined to identify and quantify soil K resources including the partitioning of K between minerals. Two or three cuts were taken annually and herbage yield and composition together with exchangeable soil K were analysed. Herbage yield declined with time and significantly reduced when the K concentrations approached 1%. The grass K concentration also declined over time and stabilized at around 0.5–0.7% (dw) in K0 in all cuts. Input-output mass balances showed an accumulated net K off-take (deficit) of 1,100 kg ha, i.e. 35 kg ha yr. With an exchangeable K pool of 100 kg ha (in the rooting zone 0–40 cm) this indicated a substantial release of K from mineral sources, most probably biotite and hydrobiotite. Assuming a similar net off-take was continued then this particular mineralogical K source would be depleted within two centuries. The study illustrates the strength of combining long-term field experimental data with state of the art quantitative mineralogical methods in order to assess site-specific resources which can form a basis to evaluate the sustainability of different management practices. [ABSTRACT FROM AUTHOR]

Organic farming largely depends on animal manure as a source of phosphorus (P) and the recycling of animal manure globally is becoming increasingly important. In a pot experiment, using radioactive P labeling techniques, we studied ryegrass uptake of P applied with animal manure and water soluble mineral fertilizer to soils that had been cropped for 22 years according to organic or conventional farming practices. The soils differed in P status and microbial activity. Labeling soil-available P also allowed assessing the uptake from residual P that remained in the soils because of their different fertilization histories. On each soil, recovery of fresh manure P in four harvests of ryegrass shoots was lower than recovery of mineral P. It ranged from 24% to 35% for manure P and from 37% to 43% for mineral P. Recovery of fresh manure P was affected by soil-available P contents. It was lower at a higher available P in a conventional soil. Different levels in microbial activity among soils were of lesser importance for the recovery of fresh manure P in plants. The recovery of residual P ranged from 9% to 15%. Residual P contained in organic cropped soils contributed less to P nutrition of ryegrass than the residual P contained in conventional cropped soils, probably due to their lower residual P contents being composed of stable P forms. The indirect isotope dilution technique is useful in assessing manure P uptake by plants, but attention must be given to added P interactions, i.e., the potential impact of organic amendments on P uptake from non-labeled soil and residual P. [ABSTRACT FROM AUTHOR]

The influence of long-term treatment and soil type on sulfur (S) flow patterns within soil and from soil to plant was studied in a pot experiment with Italian rye grass ( Lolium multiflorum cv. SW Fredrik) with (+S) or without (-S) added S. Soil samples were taken from two field treatments (farmyard manure (FYM) application or crop residue (CR) incorporation) at four sites with differing soil types within the Swedish long-term fertility experiment series. To follow gross processes, the initial soil sulfate pool was labeled with carrier-free HSO. The –S treatment resulted in visual symptoms of S deficiency, reduced biomass production and lower total S uptake by the rye grass. The isotopic measurements revealed that more than two thirds of the plant S was derived from non-labeled soil organic S, even in the + S treatment, and that all organic S pools (physically unprotected/protected and residual organic S) in the soil were involved in the S transformations. The long-term FYM treatment had resulted in higher S cycling rates and a slightly higher resistance to S deficiency than the CR treatment. The influence of soil type on S flow patterns was important, but probably only partly related to the soil S properties. [ABSTRACT FROM AUTHOR]

Selenate fertilization is an effective way to secure selenium (Se) nutrition in Se-poor areas but the cycling of the added selenate in the soil-plant system requires further clarification. We examined the Se uptake efficiency of wheat and ryegrass and Se distribution within these plants in two pot experiments. The behaviour of added selenate in a sand soil under wheat was monitored by sequential extractions during a ten-week growing period. In addition, the relationship between Se uptake of ryegrass and the salt extractable and ligand exchangeable Se in a sand and silty clay soil were studied. The added selenate remained mainly salt soluble in the soil throughout the monitoring. Se uptake by wheat comprised 12% of the soluble Se pool in soil and extended over the whole period of growth. In wheat, over 50% of Se accumulated in grains. The Se uptake of ryegrass comprised, on average, 40% of the soil salt soluble Se. In ryegrass, over 80% of the Se accumulated in roots. The distribution pattern of Se in plants can clearly have a major influence on both the Se cycle in soil and the nutritional efficiency of Se fertilization. The simple salt extraction showed fertilization-induced changes in the soluble soil Se pool, whereas the ligand exchangeable Se fraction reflected the difference in the nonlabile Se status between the two soils. [ABSTRACT FROM AUTHOR]

C and N mineralization kinetics of 25 catch crop (CC) residues, whose organic C:N ratio varied from 9.5 to 34.0, were studied during soil incubations under controlled conditions. Decomposition rates were rather similar for the different CC residues, 59% to 68% residue-C being mineralized after 168 days incubation. C mineralized during the first weeks was mainly correlated to the soluble C content of the residue. N mineralized from CC residues was much more variable (−4.9 to +38.0 mg N g−1 added C at day 168), and was mainly related to the organic N content in residues. C and N mineralization kinetics were simulated with STICS residue decomposition model, using the previous parameterization mostly based on mature crop residues (Nicolardot et al. Plant Soil 228:83–103, ). A reasonable agreement was found between measured and simulated C kinetics but N mineralization was underestimated by the model. A new parameterization was carried out to improve N predictions. The fitting procedure was first applied independently to each CC residue in order to optimise the five parameters of the model. The relationships found between each optimised parameter and the C:N ratio of CC residues were similar to those obtained previously, indicating that the same model was applicable to all residues. The parameters of these relationships were fitted on a combined dataset including CC and mature residues. The new parameterisation lead to better simulations for CC residues, the errors of prediction (RMSE) for C and N mineralization being 32 and 1.8 mg g−1 added C, respectively. For the whole dataset (68 residues), the RMSE were 50 and 3.3 mg g−1 added C. The prediction quality is satisfactory with respect to the model simplicity and the single criterion of residue quality (C:N ratio). [ABSTRACT FROM AUTHOR]

Soil moisture content (SMC) and throughfall were monitored along transects between rows of radiata pine ( Pinus radiata D. Don) planted at 7 m row spacing and grown with ryegrass/clover or lucerne pastures or with no understorey. SMC was recorded to 1 or 2 m depths for years 2–6 or 4–6, respectively. The predominant rainfall from the south–south–west (SSW) direction created rain shadows (60% of open pasture) on the northern sunny side of the trees. The rain shadows increased as the trees grew but their position were modified by stand pruning and thinning in years 4 and 5. SMC in the top meter showed strong positional effects with the lowest SMC under the tree crowns and on the northern side. There were strong seasonal patterns driven by high spring and summer evapotranspiration, modified by rain shadows and stand age. For the no-understorey treatment, SMC remained high midway between tree rows until the trees were 4 years old and started utilizing this moisture. For the two pasture understoreys, the difference in SMC between the north and south sides decreased with time after trees were thinned and pruned. In the no-understorey there was little difference between the two aspects. Understorey evapotranspiration and fine rooting patterns also helped explain soil moisture use patterns. No difference was detected between two contrasting radiata pine tree types. The effective rooting depth of the ryegrass/clover understorey was <0.7 m while that of lucerne and trees were deeper. Alternative tree planting practices may reduce some of the negative effects of tree-understory moisture competition. [ABSTRACT FROM AUTHOR]

Selenium (Se) is an essential micronutrient for animal and human nutrition, but whether it is essential to plants remains controversial. However, there are increasing experimental evidences that indicate a protective role of Se against the oxidative stress in higher plants through Se-dependent glutathione peroxidase (GSH-Px) activity. The effects of the Se chemical forms, selenite and selenate, the rate of their application on shoot Se concentration and their influence on the antioxidative system of ryegrass ( Lolium perenne cv. Aries), through the measurement of GSH-Px activity and lipid peroxidation, were evaluated in an Andisol of Southern Chile. Moreover, a soil–plant relationship for Se was determined and a simple method to extract available Se from acid soils is proposed. In a 55-day experiment ryegrass seeds were sown in pots and soil was treated with sodium selenite or sodium selenate (0–10 mg Se kg−1). The results showed that the Se concentration in shoots increased with the application of both selenite and selenate. However, the highest shoot Se concentrations were obtained in selenate-treated plants. For both sources of Se, there was a significant positive correlation between the shoot Se concentration and the GSH-Px activity; and the Se-dependence of this enzymatic activity was related especially with the chemical form of applied Se rather than the Se concentration in plant tissues. Furthermore, the lipid peroxidation, as measured by Thiobarbituric Acid Reactive Substances (TBARS), decreased at low levels of shoot Se concentration, reaching the lowest level at approximately 20 mg Se kg−1 in plants and then increased steadily above this level. In addition, the acid extraction method used to evaluate available Se in soil showed a positive good correlation between soil Se and shoot Se concentrations irrespective of chemical form of Se applied. [ABSTRACT FROM AUTHOR]

A field experiment was carried out over 12 months to determine the effect of animal treading on N2 fixation in a mixed white clover-ryegrass pasture. The experimental site was defoliated by mowing for the duration of the study. A single treading event of moderate or severe pugging intensity was initiated in plots during wet spring conditions by using dairy cows at varying stocking rates (4.5 cows 100 m−2 for 1.5 or 2.5 h, respectively). Inputs of dung and urine onto the plots was avoided by overnight housing of the cows and interception of excreta during the pugging event. Soil air-filled porosity decreased from 21% in the non-pugged control to 15–16% in pugged treatments by day 3. Bulk density of soil was not significantly affected by pugging. Soil inorganic N concentration increased in pugged treatments, and was 4-fold greater on day 28 in severely pugged plots compared to non-pugged plots. White clover plant density and plant size was markedly lower in pugged treatments (up to 85% and 72% reduction, respectively under severe pugging). White clover growth was most affected during the first 156 days after pugging (up to 90% decrease under severe pugging), leading to an annual clover dry matter production loss of 9% and 52%, respectively. The proportion of clover N derived from atmospheric N2 (%Ndfa; estimated by 15N dilution) was initially reduced (to a lower limit of 43%) by severe pugging (days 28–71) before recovery to control levels (90%) by day 91. Annual N2 fixation in clover herbage decreased significantly from 76 kg N ha−1 yr−1 in the non-pugged control, to 66 and 36 kg N ha−1 yr−1 under moderate and severe pugging, respectively. Most of this difference was evident within the first 156 days after pugging. Our data indicates that the major loss in fixed N2 input under pugging was due to reduced clover growth and production resulting from pugging damage and loss of residual white clover biomass by hoof action. [ABSTRACT FROM AUTHOR]

The aim of the present study was to determine long-term K release rates from soil by use of a modified resin method, where vigorous agitation and soil-resin separations were avoided to minimise the dissolution of the soil minerals. Resins saturated with Ca2+ or H+ were tested; Ca2+ because it is the most dominating cation on the soil exchange complex, and H+ because it is an important K+ counter-ion released from plant roots. The tested soil: resin systems included two rates of agitation; no agitation, and gentle agitation where the soil particles visually did not move relative to each other. The resin beds were kept physically separated from the soil particles by use of a specially designed extraction tube. Three soils of the same mineralogical and textural origin, but exposed to different K input levels during more than 80 years, were used. A pot experiment with ryegrass was carried out using the same three soils. Vigorous shaking of the resin-soil systems was not needed to obtain a sufficiently high and rapid K release to the resin; even without agitation long-term K release rates could be determined. The accumulated K release was in all combinations of agitation rate, resin saturation ion and soil K status proportional to the square root of extraction time after 1000 h of extraction, indicating diffusion controlled K release from the minerals. Resin extractable K was closely correlated with ryegrass K uptake, indicating similarity in the extraction process. In contrast, K extracted with ammonium acetate or nitric acid did not provide information about the ability of the soils to release K in the long term. Based on the criteria :(i) substantial K adsorption under slow K release conditions; and (ii) achievement of a stable long-term K release within a limited extraction period, the Ca-saturated resins with gentle agitation and H-saturated resins without agitation are concluded to be best suited for routine laboratory work. [ABSTRACT FROM AUTHOR]

The objective of the present work was to develop a method to distinguish between metabolically inactive and active parts of plant roots. White clover (Trifolium repensL.) roots were stained with 2,3,5-triphenyltetrazolium chloride (TTC) followed by root colour classification with an interactive scanner-based image analysis programme (WinRHIZO). Roots inactivated by boiling were unstained and pale brown, whereas fresh samples with predominantly metabolically active roots turned dark red, red or pale red after staining. A small amount of very young, presumable active roots (0.8% of total active root length) failed to stain red with TTC. The colour analysis of inactive and active roots was based on four colour classes for boiled roots and seven classes for fresh roots, respectively, as defined upon visual examination of images. Pixel colours falling outside the defined classes were allocated to the nearest defined class - an option that increased objectivity and stability and reduced the required number of colour classes. For the fresh white clover roots, 75-86% of the total root length was determined as active, while 3-7% of the boiled roots fell into the same category. The percentage of total root length measured by WinRHIZO that was identified as metabolically active was linearly correlated with the percentage of fresh roots in mixtures of fresh and boiled roots (R2=0.99). Colour classes chosenà priorifrom one experiment could be used to distinguish fairly satisfactorily between active and inactive roots of another white clover cultivar grown under other conditions, but failed to classify activity in ryegrass (Lolium multiflorumLam.) root samples. In the latter case, colour classes needed to be re-defined in order to produce reliable data. Our work shows that WinRHIZO’s colour identification sub-module provides a new promising tool to classify root activity as identified after staining with TTC, but colour classes must be carefully evaluated on every new occasion. [ABSTRACT FROM AUTHOR]

The objective of this work was to determine if the impact of nitrogen (N) on the release of organic carbon (C) into the soil by roots (rhizodeposition) correlated with the effect of this nutrient on some variables of plant growth.Lolium multiflorumLam. was grown at two levels of N supply, either in sterile sand percolated with nutrient solution or in non-sterile soil. The axenic sand systems allowed continuous quantification of rhizodeposition and accurate analysis of root morphology whilst the soil microcosms allowed the study of14C labelled C flows in physico-chemical and biological conditions relevant to natural soils. In the axenic sand cultures, enhanced N supply strongly increased the plant biomass, the plant N content and the shoot to root ratio. N supply altered the root morphology by increasing the root surface area and the density of apices, both being significantly positively correlated with the rate of organic C release by plant roots before sampling. This observation is consistent with the production of mucilage by root tips and with mechanisms of root exudation reported previously in the literature, i.e. the passive diffusion of roots solutes along the root with increased rate behind the root apex. We proposed a model of root net exudation, based on the number of root apices and on root soluble C that explained 60% of the variability in the rate of C release from roots at harvest. The effects of N on plant growth were less marked in soil, probably related to the relatively high supply of N from non-fertiliser soil-sources. N fertilization increased the shoot N concentration of the plants and the shoot to root ratio. Increased N supply decreased the partitioning of14C to roots. In parallel, N fertilisation increased the root soluble14C and the14C recovered in the soil per unit of root biomass, suggesting a stimulation of root exudation by N supply. However, due to the high concentration of N in our unfertilised plants, this stimulation was assumed to be very weak because no significant effect of N was observed on the microbial C and on the bacterial abundance in the rhizosphere. Considering the difficulties in evaluating rhizodeposition in non sterile soil, it is suggested that the root soluble C, the root surface area and the root apex density are additional relevant variables that should be useful to measure along with the variables that are commonly determined when investigating how plant functioning impacts on the release of C by roots (i.e soil C, C of the microbial biomass, rhizosphere respiration). [ABSTRACT FROM AUTHOR]

There is ample experimental evidence that, Na, if supplied in separate fertiliser granules or crystals to N, i.e., in blended fertiliser form, can improve both the yield and the recovery of fertiliser N by grassland swards in situations of limited K supply, but not in situations of K abundance. There is some evidence, though, that in K-replete situations, Na, if supplied in the same fertiliser granule as N, i.e. in concentrated complex fertiliser (CCF) form, also improves dry matter production and N recovery by swards whilst lowering the risk of grass tetany in grazing animals. However, the mechanism for the latter effect of Na on N uptake has never been elucidated, nor has it been clarified whether Na stimulates NHand NOuptake by plants or simply NOuptake alone. The aim of the present study was to see if supplying Na in the same fertiliser pellets (NNa-CCF) as NH4NO3 (differentially labelled with15N), or in separate pellets (NNa-blend), had any effect on the recovery of15N-labelled NHand NO-N by perennial ryegrass plants growing in a glasshouse under K-replete conditions. The results of the experiment confirmed that using an NNa-CCF was more beneficial to shoot production than using an NNa-blend. However, the differential in shoot production occurred without any corresponding difference in total N (i.e. NHplus NO-N) recovery in shoot tissue. Instead, Na, in the CCF appears to have stimulated NOuptake at the expense of NHabsorption, thereby altering the balance between NHand NO-nutrition in favour of NO-nutrition, and stimulating shoot production as a consequence. It was concluded that if grassland is already well supplied with K it would be more beneficial in terms of sward production to apply a Na and N-containing CCF than a blend of separate Na and N-containing granules or crystals. [ABSTRACT FROM AUTHOR]

It has been demonstrated that the use of living mulches solves some of the environmental problems associated with the conventional cropping of maize (Zea mays L.). However, plant growth and yield are often reduced in such a cropping system. Since shoot competition between the main crop and the cover crop can be avoided by regular cutting of the cover crop, it was hypothesized that decreases in maize growth and yield in a living Italian ryegrass (Lolium multiflorum Lam.) mulch must be related to below ground interactions between the two species and that these may be traced back to the characteristics of their root systems. Two cropping systems, maize grown alone in bare soil (conventional cropping, BS) or together with a living Italian ryegrass mulch (LM), were studied in lysimeters (1.0 m2 surface area and 1.1 m depth) placed outdoors, near Zurich Switzerland, for a duration of three years. In the LM treatment a strip, 0.3 m wide, in the center of the plot around the maize row was free of grass. For comparison, an Italian ryegrass (RG) treatment, managed as the LM treatment but without maize plants, was also included in the study. Minirhizotrons (54 mm inner diameter) were horizontally installed at ten soil depths between 0.0 and 1.0 m, perpendicular to the orientation of the maize rows. The development of the maize shoot and the rooting patterns were observed non-destructively. LM strongly modified the maize crop by decreasing growth and duration of the leaf area, and thus biomass and grain yield at harvest by as much as 78 and 72%, respectively. Maximum root densities in the three treatments were observed around the time of maize anthesis. However, BS maize was unable to build up root densities similar to those observed in Italian ryegrass plots at the time of maize sowing. The root densities of the LM and the RG treatments were usually similar. The inability of the maize plants to establish a competitive root system in the LM limits the supply of nutrients and water and therefore reduces growth and yield. Improving the productivity of maize in living mulches will depend on the ability to achieve a better separation of the rooting volumes of the two species, so that specific steps to facilitate the main crop and control the living mulch can be taken. [ABSTRACT FROM AUTHOR]

Water and nitrogen availability may limit the growth of the main crop competing with a cover crop in a living mulch system. Some aspects of the dynamics of water (soil water content and deep percolation) and nitrogen (concentration in soil solution and leachate) were studied in maize (Zea mays L.) sown into a bare soil (BS, conventional cropping) or into a living Italian ryegrass (Lolium multiflorum Lam.) mulch (LM) during three years. Eight lysimeters (1.0 by 1.0 m square surface area and 1.1 m deep) with ceramic suction cups, TDR probes and a drainage pipe were used each. In LM a 0.3 m wide strip was kept free of grass around the maize row. The living mulch reduced the soil water content between 0.3 and 0.9 m soil depth, which remained lower even after intense rainfall. Deep percolation over the entire maize crop season was at least 40% lower in the LM compared to the BS treatment. In LM the nitrate concentrations in the soil solution and in the leachate (usually < 10 mg L-1) were very low. In BS the nitrate concentration in the leachate reached as much as 70 mg L-1. Losses of N in LM did not reach 1% of the values observed in BS. Reduced water and N availability in LM contribute to explain the decrease in growth and yield of the maize plants, and are in good agreement with the dense root system developed in this cropping system as compared to BS. The challenge for the development of living mulch systems is to improve the uptake of water and nitrogen by the roots of the main crop in a competitive environment without affecting the capacity of the cover crop to prevent N losses by leaching. [ABSTRACT FROM AUTHOR]

Rhizodegradation of recalcitrant organic pollutants, such as polycyclic aromatic hydrocarbons (PAH), may benefit from the major role that root exudates have on rhizospheric microbial processes. We investigated the influence of the proximity to ryegrass (Lolium perenne L.) roots on microbial populations and their biodegradation of phenanthrene (PHE) using compartmented pots. PAH degrading bacteria, total heterotrophic bacteria and PHE biodegradation were quantified in three consecutive sections at different distance (0–3, 3–6, 6–9 mm) from a mat of actively exuding roots. A bacterial gradient was observed with higher numbers of heterotrophs and PAH degrading bacteria closest to the roots. In parallel, a PHE biodegradation gradient was evident in the presence of roots. The biodegradation reached 86%, 48% and 36% of initially added PHE, respectively, in the layers 0–3 mm, 3–6 and 6–9 mm from the roots. The biodegradation rate was similar throughout the three layers of the non planted control. The present experimental system seems well suited for spatial and dynamic studies of PAH rhizoremediation. [ABSTRACT FROM AUTHOR]