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The determination of optimum nitrogen (N) fertilisation rates, which maximise yields and minimise N losses, remains problematic due to unknown upcoming crop requirements and near-future supply by the soil. Remote sensing can be used for determining the crop N status and to assess the spatial variability within a field or between fields. This can be used to improve N fertilisation, provided that the optimal fertilisation rate at the time of fertiliser application for an expected yield is known. Using the APSIM-wheat model, we developed an algorithm that relates the N status of the plants at early development stages to the yield response to N. Simulations were performed for winter wheat under growth conditions in Denmark. To obtain a range of different N status in the biomass at early growth stages, the soil N in autumn was varied from 20 to 180 kg N ha−1, and at BBCH23, fertiliser was applied at a rate of 50 kg N ha−1. In a full factorial setup, additional N fertiliser was applied ranging from 0 to 150 kg N ha−1 during three different development stages (BBCH30, 32, and 37). The algorithm was evaluated by comparing model outputs with a standard N application of 50 kg N ha−1 at BBCH23 and 150 kg N ha−1 at BBCH30. The evaluation showed that, depending on the N status of the soil, the algorithm either provided higher or lower optimal N fertilisation rates when targeting 95% of the maximum yield, and these affected the grain yield and the grain N, as well as the amount of N leaching. Split application of fertiliser into three applications was generally beneficial, with decreased product-related N leaching of up to nearly 30%. Further testing of the model under different environmental conditions is needed before such an algorithm can be used to guide N fertilisation. [ABSTRACT FROM AUTHOR]

The emission of nitrous oxide (N 2 O) from agricultural soils to the atmosphere is a significant contributor to anthropogenic greenhouse gas emissions. The recycling of organic nitrogen (N) in manure and crop residues may result in spatiotemporal variability in N 2 O production and soil efflux which is difficult to capture by process-based models. We propose a multi-species, reactive transport model to provide detailed insight into the spatiotemporal variability in nitrogen (N) transformations around such N 2 O hotspots, which consists of kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification represented by a system of coupled partial differential equations. The model was tested with results from an incubation experiment at two different soil moisture levels (-30 and -100 hPa) and was shown to reproduce the recorded N 2 O and dinitrogen (N 2) emissions and the dynamics of important carbon (C) and N components in soil reasonably well. The simulation indicated that the four different microbial populations developed in closely connected but separate layers, with denitrifying bacteria growing within the manure-dominated zone and nitrifying bacteria in the well-aerated soil outside the manure zone and with time also within the manure layer. The modeled N 2 O production within the manure zone was greatly enhanced by the combined effect of oxygen deficit, abundant carbon source, and supply of nitrogenous substrates. In the wetter soil treatment with a water potential of -30 hPa, the diffusive flux of nitrate (NO 3-) across the manure–soil interface was the main source of NO 3- for denitrification in the manure zone, while at a soil water potential of -100 hPa, diffusion became less dominant and overtaken by the co-occurrence of nitrification and denitrification in the manure zone. Scenarios were analyzed where the diffusive transport of dissolved organic carbon or different mineral N species was switched off, and they showed that the simultaneous diffusion of NO 3- , ammonium (NH 4+), and nitrite (NO 2-) was crucial to simulate the dynamics of N transformations and N 2 O emissions in the model. Without considering solute diffusion in process-based N 2 O models, the rapid turnover of C and N associated with organic hotspots can not be accounted for, and it may result in the underestimation of N 2 O emissions from soil after manure application. The model and its parameters allow for new detailed insights into the interactions between transport and microbial transformations associated with N 2 O emissions in heterogeneous soil environments. [ABSTRACT FROM AUTHOR]

The emission of nitrous oxide (N2O) from agricultural soils to the atmosphere is a significant contributor to anthropogenic greenhouse gas emissions. The recycling of organic nitrogen (N) in manure and crop residues may result in spatiotemporal variability of N2O production and soil efflux which is difficult to capture by process-based models. We propose a multi-species, reactive transport model to provide detailed insight into the spatiotemporal variability of nitrogen (N) transformations around such N2O hotspots, which consists of kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification represented by a system of coupled partial differential equations. The model was tested with results from an incubation experiment at two different soil moisture levels (-30 and -100 hPa, respectively) and was shown to reasonably well reproduce the recorded N2O and dinitrogen (N2) emissions, and the dynamics of important carbon (C) and N components in soil. The simulation indicated that the four populations developed in closely connected, but separate layers, with denitrifying bacteria growing within the manure-dominated zone and nitrifying bacteria in the well-aerated soil outside the manure zone and with time also within the manure layer. The modeled N2O production within the manure zone was greatly enhanced by the combined effect of oxygen deficit, abundant carbon source and supply of nitrogenous substrates. In the wetter soil treatment with a water potential of -30 hPa, diffusive flux of nitrate (NO3-) across the manure-soil interface was the main source of NO3- for denitrification in the manure zone, while at a soil water potential of -100 hPa, diffusion became less dominant and overtaken by the co-occurrence of nitrification and denitrification in the manure zone. Scenarios were analyzed where diffusive transport of dissolved organic carbon or different mineral N species were switched off, and they showed that the simultaneous diffusion of NO3-, ammonium (NH4+), and nitrite (NO2-) were crucial to simulate the dynamics of N transformations and N2O emissions in the model. Without considering solute diffusion in process-based N2O models, the rapid turnover of C and N associated with organic hotspots can not be accounted for, and it may result in underestimation of N2O emissions from soil after manure application. The model and its parameters allow for new detailed insights into the interactions between transport and microbial transformations associated with N2O emissions in heterogeneous soil environments. [ABSTRACT FROM AUTHOR]

Performance of the APSIM (Agricultural Production Systems sIMulator) wheat model was assessed to simulate winter wheat phenology, biomass, grain yield, and nitrogen (N) uptake for its potential to optimize fertilizer applications for optimal crop growth and minimal environmental degradation. The calibration and evaluation dataset had 144 and 72 different field growing conditions (location (~7) × year (~5) × sowing date (2) × N treatment (7–13)), respectively, and included seven cultivars. APSIM simulated phenological stages satisfactorily with both model calibration and evaluation data sets with r2 of 0.97 and RMSE of 3.98–4.15 BBCH (BASF, Bayer, Ciba-Geigy, and Hoechst) scale. Simulations for biomass accumulation and N uptake during early growth stages (BBCH 28–49) were also reasonable with r2 of 0.65 and RMSE of 1510 kg ha−1, and r2 of 0.64–0.66 and RMSE of 28–39 kg N ha−1, respectively, with a higher accuracy during booting (BBCH 45–47). Overestimation of N uptake during stem elongation (BBCH 32–39) was attributed to (1) high inter-annual variability in simulations, and (2) high sensitivity of parameters regulating N uptake from soil. Calibration accuracy of grain yield and grain N was higher than that of biomass and N uptake at the early growth stages. APSIM wheat model showed high potential for optimizing fertilizer management in winter wheat cultivation in Northern Europe. [ABSTRACT FROM AUTHOR]

Studies evaluating the complexity of models, which are suitable to simulate grass growth at regional scales in intensive grassland production systems are scarce. Therefore, two different grass growth models (GrasProg1.0 and APSIM) with different complexity and input requirements were compared against long-term observations from variety trials with perennial ryegrass (Lolium perenne) in Germany and Denmark. The trial sites covered a large range of environmental conditions, with annual average temperatures ranging from 5.9 to 10.3 °C, and annual rainfall from 536 to 1154 mm. The sites also varied regarding soil type, which were for modelling categorised into three different groups according to their plant available water (PAW) content: light soils with a PAW of 60 mm, medium soils with a PAW of 80 mm, and heavy soils with a PAW of 100 mm. The objective was to investigate whether the simple model performed equally well with the given low number of inputs, namely climate and PAW group. Evaluation statistics showed that both models provided satisfactory results, with root mean square errors for individual cuts ranging from 0.59 to 1.28 t dry matter ha−1. The model efficiency (Nash–Sutcliffe efficiency) for the separate cuts were also good for both models, with 81% of the sites having a positive Nash–Sutcliffe efficiency value with GrasProg1.0, and 72% with APSIM. These results reveal that without detailed site-specific descriptions, the less complex GrasProg1.0 model can be incorporated into a simple decision support tool for optimising grassland management in intensive livestock production systems. [ABSTRACT FROM AUTHOR]

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Knowledge about pasture growth rates is crucial for optimizing forage use efficiencies in intensively managed pasture and silage-based dairy systems, enabling optimized cutting/grazing times for high yields with high forage quality. The aim of this study was to parameterise a simple model, GrasProg, for predicting pasture growth in an intensively managed dairy production system under a cut-and-carry management. For this, pasture crop-growth rates were measured over a period of two years (2016 and 2017) at five contrasting sites in Schleswig-Holstein, Northern Germany. The pastures received nitrogen (N) fertilizer at a rate of 280 kg N ha−1 and were cut on a four-week interval. Average annual dry matter (DM) yields ranged from 10.9 to 11.6 t/ha for the three different locations. The DM accumulation simulated by GrasProg matched actual measurements over the varying intervals well (R2 = 0.65; RMSE = 49.5 g DM m−2; and NSE = 0.44). Two model parameters were adjusted within the vegetation period, namely, the relative growth rate, a proxy of the number of generative tillers, and the initial biomass at the start of each growth period, a proxy for the tillering density. Both predicted and measured pasture growth rates showed the same typical seasonal pattern, with high growth rates in spring, followed by decreasing growth rates to the end of the vegetation period. These good calibration statistics, with adjusting of only two model parameters, for the different sites and different climatic conditions mean that GrasProg can be used to identify optimum grazing or cutting strategies, with optimal yield and forage quality. [ABSTRACT FROM AUTHOR]

Keeping cover crops to reduce nitrogen leaching often conflicts with timing tillage operations before the soil becomes un-trafficable during winter, while leaving cover crops in the field until spring raises concerns over pre-emptive competition with the following crop. Therefore, farmers may resort to tilling their fields in autumn after letting cover crops remain in the fields for only a short period of time. We explore the effects of this practice in a laboratory lysimeter setting by analyzing the leaching of nitrate from intact topsoil cores. Cores were extracted from no-till (NT) plots and plots tilled in autumn (AuT), in areas kept bare (B) and with volunteer winter rye plant cover (V) after harvest. Nitrate breakthrough curves show that V significantly reduced N leaching by 61% relative to B in NT, but did not have a significant effect in AuT. Dissection of leached cores and undisturbed reference cores indicated a significant removal of mineral N from the soil during the lysimeter experiment for all treatments except V in NT. This indicates that volunteer cover removed a crucial amount of leachable N and suggests that tillage counteracted the effect of V in AuT, likely due to a combination of reduced uptake and re-mineralization of N in cover crop residue. [ABSTRACT FROM AUTHOR]

Early sowing of winter cereals has been promoted as an alternative to catch crops for reducing nitrogen (N) leaching in intensively managed cropping systems. Underlying data for this are, however, scarce and it is unclear how year‐to‐year variations affect potential reductions in N leaching. Well‐tested cropping system models can be used to assess the impact of early sowing on crop yield and N leaching. We tested the ability of the Agricultural Production System Simulator (APSIM) to simulate grain yield, biomass, phenology, N uptake and N leaching from timely and early‐sown winter cereals. The evaluation was based on two extensive field experiments carried out in Denmark in continuous winter cereals systems with different N fertilization applications, and a farm experiment in Germany with a grass ley/winter wheat crop sequence and two different N fertilization rates. Additionally, observations from growth stages throughout Denmark were used. After changing a few crop model parameters, APSIM reproduced the general effects of N fertilization and crop sequence on yields and N uptake, as well as N leaching. The model was then used to simulate the effect of sowing time on grain yield over a period of 10 years, to capture year‐to‐year variability and enable a better evaluation of the efficacy of early sowing for reducing N leaching. In the continuous winter cereal systems, early sowing reduced N leaching at both sites in Denmark. In contrast, in the grass ley/winter wheat system in Germany early sowing increased N leaching, due to enhanced mineralization of grass residues. [ABSTRACT FROM AUTHOR]

Optimum nitrogen (N) fertilization, which aims for high productivity while minimizing N losses to the environment, requires a better understanding of the N leaching behaviour around the recommended N rate. A study was conducted with increasing N fertilization levels over 3 years (2016–2019) with early and timely sown winter cereals (rye and wheat) at two sites in Denmark with different climatic conditions. For winter rye N fertilizer application rates ranged from 0 to 258 kg N ha‒1, and for winter wheat from 0 to 300 kg ha‒1. Grain yields did not respond much to the N application above the recommended rate. Nitrate (NO3) leaching was very low in the first period, but increased in the second and third period. The effect of a potential N carry‐over on marginal N leaching (defined as the additional N leaching per unit of additional N fertilizer applied) is large. Under early sown winter rye, marginal N leaching is reduced from 36 to 14 kg N ha‒1 in the third period following N fertilization of the recommended rate of 170 kg N ha‒1 when carry‐over was accounted for, and under the timely sown winter rye from 68 to 24 kg N ha‒1. Our results show that marginal N leaching around the recommended rate is almost linear at the study site, when carry‐over is accounted for. Thus, the use of precision agriculture, with lower fertilization application rates to areas with high residual soil N, is less effective compared with sites, which have an exponential leaching behaviour. [ABSTRACT FROM AUTHOR]

BACKGROUND: Nitrogen (N) fertiliser used on crops is among the main sources of water pollution. Reliable measurement of N losses from land uses in catchments is key to designing effective management strategies that minimise those losses at the same time as keeping farms profitable. In the present study, we used a management simulation tool within the Agricultural Production Systems sIMulator (APSIM) to assess the effect of fertiliser management on N leaching from croplands in the Aparima catchment in Southland, New Zealand. The assessment was based on two N‐fertiliser regimes: (i) Scheduled (conventional) where, N‐fertiliser rates and timing of application followed a prescribed programme, and (ii) Soil‐test where, N‐fertiliser rates and timing depended on daily analysis of simulated soil N levels. Four rotations (continuous wheat, pasture‐wheat‐grain oats, wheat‐fodder beet‐peas and wheat‐green oats‐fodder beet‐peas) were used in the evaluation. RESULTS: APSIM simulated crop productivity with reasonable accuracy. Yields were 2% greater, fertiliser N input was 11% lower and leaching was 20% lower under the Soil‐test compared to the Scheduled fertiliser management. These results show the potential of a Soil‐test based fertiliser application to increase fertiliser‐N use efficiency and reduce the risk of N loss to the Southland catchment water systems. CONCLUSION: The present study demonstrates a dynamic farm systems model can be a viable tool to generate valuable data for assessing the productivity and environmental effects of cropping systems at a catchment scale. © 2021 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Yield increases in forage maize (Zea mays L.) in NW Europe over time are well documented. The driving causes for these, however, remain unclear as there is little information available regarding the role of plant traits triggering this yield progress. Ten different hybrids from the same maturity group, which have typically been cultivated in Northwest Germany from 1970 to recent and are thus representing breeding progress over four decades, were selected for a 2-year field study in northern Germany. Traits that were investigated included leaf area index, leaf architecture, photosynthesis, radiation use efficiency, root mass, root length density, and turnover. Based on a mixed model analysis with these traits as co-variates, parameters related to leaf characteristics, in particular the number and length of leaves, the radiation use efficiency, and the leaf orientation, were identified as most influential on the yield progress (0.13 tons ha-1 year-1). In contrast to our hypothesis, root biomass only increased negligibly in newer hybrids compared to older ones, confirming the 'functional equilibrium' theory for high input production systems. Due to an abundance of nutrients and water in such high input systems, there is no incentive for breeders to select for carbon partitioning toward the rooting system. Breeding evidence to increase forage quality were also negligible, with no change in cob starch concentration, forage digestibility, nor NDF content and NDF digestibility. The observed increase in yield over the last four decades is due to a combination of increased temperature sums (~240 GDD within 40 years), and a higher radiation interception and radiation use efficiency. This higher radiation interception was driven by an increased leaf area index, with a higher number of leaves (16 instead of 14 leaves within 40 years) and longer leaves of newer compared to older hybrids. Future selection and adaptation of maize hybrids to changing environmental conditions are likely to be the key for high productivity and quality and for the economic viability of maize growing and expansion in Northern Europe. [ABSTRACT FROM AUTHOR]

Purpose: Photolith morphotypes differ between plant species which can be utilized to reconstruct past vegetation. More recently, the role of phytoliths in soil carbon (C) storage and soil C and silicon (Si) cycling has received increasing attention. The aim of this study was to investigate the impact of recent land cover change on soil phytolith assemblage, soil phytolith concentration, and phytolith-occluded carbon (PhytOC) storage.Materials and methods: Mineral soil samples (0-10 cm) were collected from a tussock grassland (n = 18) and an adjacent 32-year-old pine forest (n = 21) in Otago, New Zealand. The pine forest was established on tussock grassland. Microwave digestion was followed by sedimentation and flotation procedures to obtain a purified phytolith extract to identify soil phytolith morphotypes by microscopy and to quantify PhytOC concentrations using an elemental analyzer.Results and discussion: Soil phytolith assemblage was similar under tussock grassland and pine forest. Bulliform and short cells which were derived from grass species accounted for more than 80% of the phytoliths. Woody plant-derived phytoliths found under tussock grassland (1) may originate from shrubs which are encroaching into the tussock grassland and/or (2) are a legacy of the past woody-dominated vegetation. Soil phytolith concentration ranged between 1 and 3%. Soil PhytOC storage was 0.15 kg C/m2 and 0.14 kg C/m2 under tussock grassland and pine forest, respectively, and accounted for around 3% of total soil carbon storage.Conclusions: Soil phytolith assemblage, soil phytolith concentration, and soil PhytOC storage did not differ significantly between the tussock grassland and the pine forest that was converted from tussock grassland recently. The dominance of grass-derived phytoliths under the pine forest may reflect the legacy of the tussock vegetation which dominated the study site before the afforestation with pine in 1992. This study also revealed that the intrinsic feature of tussock grass species and the accumulation of phytoliths over centuries is likely the cause for the high soil phytolith and PhytOC concentrations. [ABSTRACT FROM AUTHOR]

Abstract: BACKGROUND: A combination of field experiment and modelling tested the hypothesis that dry summers increase the risk of nitrogen (N) leaching from pasture owing to a combination of: soil N accumulation in a dry summer; slow recovery of drought‐affected pasture in the autumn; and the resultant inefficient use of fertiliser N by the pasture. RESULTS: In the experiment, pasture response to urea and apparent N recovery in autumn after the drought was half that of irrigated pasture (7 vs 13 kg dry matter kg−1 N; 28 vs 52% apparent recovery; P < 0.05). There was more soil mineral N at the start of drainage (P < 0.001) as a result of this inefficient fertiliser N use. Modelling of pasture growth in six different drought years demonstrated that subsequent N leaching risk after rewetting was inversely related to pasture N uptake during rewetting in the autumn. CONCLUSION: When the period between post‐drought pasture recovery and the onset of drainage is short, N leaching risk increases. Nitrogen leaching is determined by the type of autumn (slow or fast growing conditions before drainage) and the amount of fertiliser N applied. The latter can be managed by a farmer, but the former cannot. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Farm-scale models were integrated with spatially discrete estimates of pasture production to examine the potential farm and regional implications of removing palm-kernel expeller (PKE) as a supplementary feed from dairy farms in Southland, New Zealand. The following two farm-production systems representing the majority of dairy farms in the region were modelled: a System 3 farm (D3; mid-intensification, with 10-20% of imported feed) and a System 4 farm (D4; mid- to high intensification, with 20-30% of imported feed). Within each system, the impact of the following four PKE options was explored: (1) a control with PKE (Baseline); (2) no PKE, with fewer cows producing the same amount of milk per cow as in Baseline; (3) no PKE, with the same number of cows producing less milk per cow than in Baseline; and (4) PKE replaced with barley grain. Barley grain provides for similar flexibility (timing of purchase and feeding), and can be sourced locally. Faced with the need to remove PKE as a dietary ingredient, farmers would benefit from adopting the second PKE option (no PKE, with fewer cows producing the same amount of milk per cow as in Baseline); farm-operating profits were reduced by only 3% (compared with 30% of System 4 farms adopting the third PKE option, i.e. no PKE, with the same number of cows producing less milk per cow than in Baseline) relative to the Baseline farms. The narrow range of mean annual nitrate-nitrogen (nitrate-N) leaching losses (estimates ranged from 30 to 33 kg N/ha) reflects similar estimates of N intake and N excreted in urine across the modelled options. Substantial amounts of barley grain would need to be transported into the region or produced locally to replace PKE. [ABSTRACT FROM AUTHOR]

Decoupling productivity and environmental pollution growth is a key objective of modern agricultural systems. The use of diverse (multispecies) pastures may contribute to this objective. Increasing the species diversity of intensively managed pastures can potentially increase annual herbage growth and N use efficiency. Here, we review the literature on simple (predominantly perennial ryegrass and white clover mixes) and diverse temperate pastures (those with three or more sown species) that address the soil-plant-animal interrelationships relevant to N leaching losses from intensive grazing systems. An analysis of trial results suggests that annual herbage yields from diverse mixtures are greater than those from simple mixtures. The review also suggests that greater species diversity in pastures can increase sward N uptake, attributable to complementarity of species through differentiation in rooting depths and seasonal plant growth activity. The presence of specific species in the sward was more relevant to herbage production and N dynamics than the number of species present in the sward, emphasizing the role of well-adapted plant functional types. The inclusion of forbs (e.g., chicory and plantain) in pastures is also shown to aid in reducing the N load of urine patches, thereby reducing the risk of N leaching from grazed pastures. To achieve the objective of increasing productivity and reducing N leaching, research questions remain around the role of species diversity on other aspects of the production system and N cycle, such as soil type and species adaptation, plant N uptake, and management of diverse pastures for successful on-farm implementation. [ABSTRACT FROM AUTHOR]

Nitrogen (N) dynamics in ley-arable cropping systems require better understanding in order to assess the potential of such systems to contribute to improved productivity and reduced nutrient losses in crop production. Large inputs of organic matter after termination of the ley phase result in increased mineralization and N availability to subsequent crops. The description and quantification of this residual N effect in ley-arable systems remains a major scientific challenge due to its variability and many influencing factors. Simulation modeling could contribute to improved understanding of N dynamics in ley-arable systems. The aim of this study was to evaluate the robustness of the Agricultural Production Systems Simulator (APSIM) to predict biomass yield, N yield, and N leaching of different forage maize systems in northwest Europe, while using two different approaches to predict the residual N effect. The evaluation was based on three field experiments covering plant phenology, biomass, N yield, and N leaching over several years. Model adjustments were necessary to describe mineralization of organic matter and release of N after ploughing of the grass leys. For this purpose, three scenarios were investigated by accounting for either (1) aboveground grass residues; (2) above- and belowground grass residues, both with the generic turnover approach in the model; or (3) N release depending on the carbon-to-N ratio of the residue compiled in a simple mineralization model (SMM). The results showed that APSIM-simulated biomass and N yield of maize were reasonable to poor across the different systems and sites, regardless of using the residue-related approach. The SMM performed more accurately compared to the generic turnover approach in predicting N leaching in a maize following a grass-clover ley. However, for all scenarios, APSIM had difficulties to predict a delay of N leaching observed in the experimental data after a pure ryegrass ley. In conclusion, the process description in APSIM related to organic matter mineralization in ley-arable systems under northwest European pedo-climatic conditions needs improved accounting of belowground grass residues, while the SMM is of added value to improve N mineralization patterns and leaching after a ley phase. [ABSTRACT FROM AUTHOR]

The simultaneous retention of both cations and anions due to ion-pair adsorption (IPA) has been identified in several soils. The mechanism controlling IPA is nor yet understood, however, and the mathematical description of this phenomenon is only incipient. In this study, a parameterization analysis was performed using a recently proposed adsorption model that considers the occurrence of IPA. The model, which has two alternative approaches to describe IPA, has been shown in a previous study to describe experimental data reasonably well. That analysis was incomplete, however, as the parameter uncertainties were not estimated. In this study, with the paramererization procedure using the maximum-likelihood method, a robust estimation of the model parameters, including the analysis of their uncertainties, was developed. The model was fitted to a data set obtained in batch experiments using the variable-charge Egmont soil, from New Zealand, and a comprehensive combination of SO4 and Ca concentrations. This procedure allowed the analysis of some of the underlying model characteristics and also some inferences about the IPA phenomenon. Overall, it was shown that the proposed adsorption model is a useful tool for the modeling of solutes in soils where IPA occurs. [ABSTRACT FROM AUTHOR]

To evaluate the long-term effect of wastewater application on soil physical properties, two treatment sites, close to Taupo and Levin, New Zealand, and non-irrigated control sites were compared. The soil at Taupo was a silt loam and has received wastewater application for 12 years. The soil at Levin is a sand, and has been wastewater irrigated for 22 years. The disposal blocks at both sites had a higher pH, a higher organic matter (OM) content, a lower bulk density, and thus higher total porosity, but a lower macroporosity than the control sites. The disposal block at the Levin site showed a higher hydrophobicity than the control block, which coincided with the higher soil carbon. In contrast, the Taupo soil showed a higher hydrophobicity at the control site, the site with the lower OM content. Long-term wastewater irrigation resulted in a higher aggregate stability, and changes of the total porosity following stress application were lower, suggesting higher internal soil strength. The hydraulic conductivity close to saturation was also higher in the disposal blocks. The soil mechanical strength, as determined by the precompression stress value was, however, slightly lower in the disposal blocks and not correlated with the aggregate stability. [ABSTRACT FROM AUTHOR]

PIXE is used for the elemental analysis of CCA treated timber samples, because of the simplicity of sample preparation, in-situ measurement of metal distribution, high sensitivity and the large number of samples which can be measured in a short time (typically less than 15 min per sample). The concentrations of Cr, Cu and As in the thin sections of treated poles from a vineyard were measured at 2 cm intervals from the centre of the pole. PIXE analysis indicated that in the case of fresh CCA treated timber the concentrations of Cu, Cr and As varied little with depth. In aged timber, the concentrations increased from the centre of the pole to the surface, indicating horizontal migration of these elements. The increase was greater for aged poles than for freshly treated poles, indicating surface migration of the CCA chemical with weathering. This was supported by data obtained in leaching experiments that indicated elevated concentrations of these metals in the extractants. [ABSTRACT FROM AUTHOR]

Ion retention in variable-charge soils can be enhanced by the presence of certain ions with opposite charge, thereby influencing the movement of these ions through the soil profile. Studies examining these interactions are still incipient, however, especially regarding its modeling. We present results from batch and miscible displacement experiments describing Ca2+ and SO42- movement in a variable-charge soil from New Zealand. Evidence was found for ion-pair adsorption (IPA) of both Ca2+ and SO42- The results were modeled using the convection-dispersion equation (CDE), coupled with two different mathematical approaches proposed to account for IPA. The first approach related IPA to the single soil adsorption capacity, which is governed by particle-surface phenomena. For the second approach, IPA was related solely to the soil solution concentration. Both these approaches described the adsorption data from the batch experiment reasonably well, as well as the breakthrough curves from the miscible displacement experiments. The first approach showed better overall agreement. Significant differences were found, however, when the adsorption parameters were identified by fitting models to data from either batch or miscible displacement experiments. Although more studies are needed to better understand IPA, our results showed that the extent of IPA can be large and it should not be ignored when predicting SO42- and Ca2+ movement in variable-charge soils. [ABSTRACT FROM AUTHOR]

Allophanic top‐ and subsoils from the Mexican and Newzealand Central Volcanic Plateau, as well as a nonallophanic sandy loam soil, were sampled to study the impact of organic matter and allophane content on 2,4‐D fate. High sorption rates were found, especially in the two topsoils from Mexico and New Zealand, with distribution coefficient (Kd) obtained from displacement experiments in packed columns equal to 7.61 and 8.43 L kg-1 respectively. 2,4‐Dichlorophenoxyacetic acid transfer through the soil columns was found to be in chemical nonequilibrium and was well predicted using a two‐site sorption model. For the two allophanic top soils, Kd obtained from batch was very different to the Kd obtained from column experiments. Either the equilibrium could not be reached in batch or the two‐site model was not able to describe the wide range of sorption sites present in the highly reactive organic matter and allophane components. [ABSTRACT FROM AUTHOR]

Determines the mechanisms prescribing the movement and uptake of chemicals in the soil of the rootzone controlled experiments that were carried out in four lysimeters growing tomatoes.

Demonstrates the time domain reflectometry (TDR) is a useful tool for monitoring the transport of inert and reactive solutes provided that the soil inhibits an increase in anion adsorption capacity with increasing soil solution concentration. Effluent concentrations; TDR measurements of water content; TDR and solute transport; TDR and modeling of solute transport.

In situ observations of the resident concentration and penetration of reactive chemical underneath a disc permeameter are used to infer the adsorption isotherm that characterizes soil-solution exchange in two structured soils. In permeameters set to the unsaturated head of −40 mm, the use of the dual tracers of inert bromide and reactive 35S, in two contrasting soils, enabled resolution of their sulfate adsorption isotherms. In Manawatu fine sandy loam, a mobile-immobile water soil, measurements of the resident concentration of 35S and Br− under the disc showed sulfate to be only weakly adsorbed. However, an analytical solution for the one-dimensional dispersive entry of reactive chemical into soil indicated that for any degree of adsorption,substantial depths of infiltration (≫200-300 mm) would be required for the adsorbed concentration ( S, mol kg−1) to reach equilibrium with the concentration of the influent solution ( c, mol L−1). But this same equation showed that under the disc, the retardation of the reactive chemical (35S) behind the inert tracer (Br−) could be used to infer the strength of the adsorption exchange. When carried out at two different concentrations, this retardation procedure can be used to infer the nonlinear Freundlich isotherm of exchange. In the Ramiha silt loam, a fully mobile water soil, different retardations were observed during concurrent unsaturated infiltration of Br− and labeled sulfate at 20 μmol L−1 and at 2 mmol L−1 SO42−. The isotherm was found to be S=2.3 c0.7. This is less than the S=3.0 c0.53 measured by the standard batch procedure on saturated 1∶5 soil solution samples. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) emissions from pastures can vary significantly depending on soil and environmental conditions, nitrogen (N) input, as well as the plant's ability to take up the N. We tested the hypothesis that legume-based N sources are characterized by significantly lower emission factors than mineral N based dairy systems. Therefore, this study monitored N2O emissions for a minimum of 100 days and up to two growing seasons across a gradient of plant species diversity. Emissions were measured from both grazed pastures and a controlled application of urine and dung using the static chamber method. About 90% of the simulated experiments' accumulated N2O emissions occurred during the first 60–75 days. The average accumulated N2O emissions were 0.11, 0.87, 0.99, and 0.21 kg ha−1 for control, dung, urine patches, and grazed pastures, respectively. The N uptake efficiency at the excreta patch scale was about 70% for both dung and urine. The highest N2O-N emission factor was less than half compared with the IPCC default (0.3 vs. 0.77), suggesting an overestimation of N2O-N emissions from organically managed pastures in temperate climates. Plant diversity showed no significant effect on N2O emission. However, functional groups were significant (p < 0.05). We concluded that legume-containing pasture systems without a fertilizer addition generally appear capable of utilizing nitrogen inputs from excreta patches efficiently, resulting in low N2O emissions. [ABSTRACT FROM AUTHOR]

For arable stockless farming systems, the integration of catch crops (CC) during the fallow period might be a key for closing the nitrogen (N) cycle, reducing N leaching and increasing the transfer of N to the subsequent crop. However, despite considerable research efforts, the fate of N in such integrated systems remains unclear. To address this, a two-year field experiment was carried out in northern Germany with different CC, including frost-tolerant and frost-killed CC. The experiment started following a two-year ryegrass/red clover ley, which was subsequently sown with a cereal (CE) or a grain legume (field pea, PE). This provided two contrasting systems with high residual N in autumn. The results showed high N uptake of the CC, ranging from 84 to 136 kg N ha−1 with PE as the pre-crop, and from 33 to 110 kg N ha−1 with CE. All CC reduced N leaching compared with the control, a bare fallow over autumn/winter. Of the various CC, the frost-killed CC showed higher leaching compared with the other CCs, indicating mineralisation of the CC residue in the later autumn/winter period. The process based APSIM (Agricultural Production SIMulator) model was used to simulate N cycling for a cereal grain legume rotation, including a frost-killed and a frost resistant CC. While the model simulated the biomass and the N uptake by the crops, as well as the reduction of N leaching with the use of CC well, it under-estimated N leaching from the frost-killed CC. The study showed that all CC were affective at reducing N leaching, but winter hard catch crops should be preferred, as there is a risk of increased leaching following the mineralisation of residues from frost-killed CC. [ABSTRACT FROM AUTHOR]