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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]

The use of suctions cups is a common practice for estimating nitrate (NO3–N) leaching under agricultural systems despite the various uncertainties associated with the approach. One major uncertainty is water flux, which is required for calculating NO3–N leaching loads from measured concentrations. Another problem is the interpolation of NO3–N concentrations between measurement days. We investigated how differences in water flux, obtained from two different models (EVACROP and APSIM), affect NO3–N leaching loads. The effect of interpolation of NO3–N concentrations based on days or drainage was also addressed. The models were set up according to a 2‐yr field experiment with spring barley (Hordeum vulgare L. Quinch) with different levels of N fertilization rates on a loamy soil at Flakkebjerg, Denmark. Due to small differences in measured NO3–N concentrations between sequential samplings, the method of interpolation did not significantly affect NO3–N leaching in the two periods investigated. Although there is no standard against which leaching losses from different approaches can be tested, results highlight that the modeling of water uptake as affected by N supply influences the amount of drainage and thus calculated NO3–N leaching. Therefore, for experiments with varying N fertilization levels, the APSIM model, which accounts for N nutrition on crop water use, is likely more accurate. For common fertilization rates, the simpler EVACROP seems appropriate. Thus, when using suction cup data for testing models or for evaluating mitigation options for nitrate leaching, the use of an appropriate model for estimating water fluxes is important. [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]

Intensification of pastoral dairy systems often means more nitrogen (N) leaching. A number of mitigation strategies have been proposed to reduce or reverse this trend. The main strategies focus on reducing the urinary N load onto pastures or reducing the rate of nitrification once the urine has been deposited. Restricted grazing is an example of the former and the use of nitrification inhibitors an example of the latter. A relevant concern is the cost effectiveness of these strategies, independently and jointly. To address this concern, we employed a modeling approach to estimate N leaching with and without the use of these mitigation options from a typical grazing dairy farm in New Zealand. Three restricted grazing options were modeled with and without a nitrification inhibitor (dicyandiamide, DCD) and the results were compared with a baseline farm (no restricted grazing, no inhibitor). Applying DCD twice a year, closely following the cows after an autumn and winter grazing round, has the potential to reduce annualized and farm-scale N leaching by ∼12%, whereas restricted grazing had leaching reductions ranging from 23 to 32%, depending on the timing of restricted grazing. Combining the two strategies resulted in leaching reductions of 31 to 40%. The abatement cost per kilogram of N leaching reduction was NZ$50 with DCD, NZ$32 to 37 for restricted grazing, and NZ$40 to 46 when the two were combined. For the range analyzed, all treatments indicated similar cost per percentage unit of mitigated N leaching, demonstrating that restricted grazing and nitrification inhibitors can be effective when used concurrently. [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]

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]

The article presents information on a study which examined a method for quantifying the impact of soil carbon management on biophysical soil properties, using two apple orchard systems in New Zealand. The soil carbon management is a significant factor for soil quality. The study analyzed the impact of the soil carbon management on biological soil properties, such as microbial biomass carbon, basal respiration, dehydrogenase activity, respiratory quotient, and physical soil properties such as aggregate stability, amount of plant-available water, conductive mean pore diameter near water saturation.

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]

Magnetic resonance imaging (MRI) was used to study the flow of water in a column 14 mm in diameter packed with glass beads. The sample was fully saturated and water was pumped through the column using a peristaltic pump, at flow rates of 125 and 250 mL h−1 This corresponds to mean velocities of 0.5 and 1 mm s−1, given a porosity of 0.46 m3 m−3 Nuclear magnetic resonance (NMR) images of the proton density and velocities within a 2‐mm slice were taken at a spatial resolution of 0.15 × 0.15 × 2 mm3 At a mean pore water velocity of 1 mm s−1 we approximated hydrodynamic dispersion using NMR‐measured velocity distributions in a 2‐mm slice through the sample. Additionally, we conducted a step pulse tracer experiment with chloride through the same column and at identical initial and boundary conditions. We fitted the convection–dispersion equation to the breakthrough curve and compared the column scale dispersion of the tracer experiment with the respective NMR estimate derived at the slice scale. [ABSTRACT FROM AUTHOR]

To determine the relative importance of the physical and chemical factors that influence the movement of heavy metals through soils, leaching experiments were carried out under conditions of constant molarity during unsaturated steady‐state water flow through a Manawatu fine sandy loam (a Dystric Fluventic Eutochrept). The movement and exchange of copper was studied in a binary Cu–Ca system. The movement of the associated anions, namely chloride and sulfate, was also monitored. The measurements were compared with predictions from the convection–dispersion equation (CDE), linked with cation exchange theory. The agreement between the measured and predicted breakthrough of sulfate and copper was good. This indicates that copper retardation in the Manawatu soil is closely related to the cation exchange capacity, and that exchange between Ca and Cu is the main process of Cu retardation in the Manawatu soil. However, copper appeared slightly later in the effluent than predicted, indicating that non‐exchange processes are also involved in copper transport. Measurements of suction cups could also be used to obtain the parameters for the CDE to describe sulfate movement through the soil. Time domain reflectometry (TDR) measurements of the bulk‐soil electrical conductivity could be used to monitor the movement of both sulfate and copper. This indicates that TDR can also be used to monitor cation transport and exchange through the soil, provided the percolating solution causes a sufficient change in the electrical conductivity. [ABSTRACT FROM AUTHOR]

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]