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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]

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]

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]

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: 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]

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]

Determines the effects of rate of nitrogen fertilizer and stocking rate on production and nitrogen fixation by white clover, Trifolium repens grown with perennial ryegrass, Lolium perenne in farmlets in Hamilton, New Zealand. Soil temperature; Pasture production and composition; Clover nitrogen fixation; Determinants of within-year variation in nitrogen fixation.

Compares estimates obtained by an indirect nitrogen dilution technique with those obtained by a direct nitrogen leaf feeding technique over two complete growing seasons in red clover-ryegrass and white clover-ryegrass mixtures under field conditions. Plant growth characteristics; Performance of the different labeling techniques; Interspecific nitrogen transfer.

Examines the water deficit and plant competition effects on growth and water-use efficiency of white clover, Trifolium repens and ryegrass, Lolium perenne. Plant materials and growth conditions; Soil water deficit treatments and transpiration measurements; Water-use efficiency and carbon isotopic composition measurements.

Discusses variations in natural abundance of 15 Nitrogen (N) in ryegrass and white clover shoot material that has been influenced by cattle grazing. Information on a source that supplies N to the crops of low external-N input farming systems; Reasons why natural abundance method can be applied for estimating the percentage of nitrogen derived from atmosphere without disturbance in animal-grazed systems.

Studies nitrogen dynamics and the growth of spring barley under the effect of the quality of incorporated residues from white clover and ryegrass. Treatments of white clover and ryegrass residues given to crops considered for the study; Measurement of carbon and nitrogen mineralization from the residues; Treatment that has produced crop with highest dry matter and nitrogen uptake.

The short-term effects of a simulated cattle dung pat on N2 fixation and total uptake of N in a perennial ryegrass/white clover mixture was studied in a container experiment using sheep faeces mixed with water to a DM content of 13%. We used a new 15N cross-labelling technique to determine the influence of dung-pat N on N2 fixation in a grass/clover mixture and the uptake of dung N in grass and clover. The proportion of N in clover derived from N2 fixation (%Ndfa) varied between 88-99% during the 16 weeks following application of the dung. There was no effect of dung onthe %Ndfa in clover grown in mixture, whereas the %Ndfa in clover grown in pure stand decreased (nominal 2-3%) after dung application. Dung did not influence the amount of N2 fixed, and the uptake of dung N in grass and clover proceeded at an almost constant rate.After 16 weeks, 10% of the applied dung N was taken up by grass and clover, 57% had been incorporated in the soil by faunal activity and 27% remained in residual dung on the soil surface. The dung N unaccounted for (7%) was probably lost by ammonia volatilisation and denitrification. The uptake of dung N in grass/clover mixtures in the field was similarly followed by using simulated 15N-labelled dung pats. The total dry matter production and N yields increased in the0-30 cm distance from the edge of the dung patch, but the proportionof clover decreased. Thirteen months after application of the dung 4% of the applied dung N was recovered in the harvested herbage, 78% was recovered from the soil and the residual dung, and 18% was not accounted for. It is concluded that N2 fixation in the dung patch border area in grass/clover mixtures is not influenced directly by the release of N from dung pats in the short term. However the amount of N2 fixed may be reduced, if the growth of clover isreduced in the patch border area. [ABSTRACT FROM AUTHOR]