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To improve agricultural sustainability, alternative cultivation methods and assessment tools need to be developed. Integrating service crops (SC) can potentially increase cropping system multifunctionality and mitigate negative climate and environmental impacts of agriculture. (1) Calibrate oats, winter wheat and red clover SC, grown as sole crops and intercrops, in the cropping system model APSIM NG for northern Europe climate conditions. (2) Use the calibrated crop modules to assess ecosystem processes from an intercropping system. (3) Discuss the role of mechanistic crop models in assessing ecosystem services and disservices from complex cropping systems. The crops were calibrated with data from an oats-winter wheat cropping sequence at two field sites. Thirty weather datasets were created from historical weather data to generate weather-dependent variability in crop performance and related processes. The assessment compared two scenarios, with or without an intercropped red clover SC sown in oats and terminated the following spring in winter wheat. Outputs representing processes related to important ecosystem services were extracted from the simulations. Calibration of the three crops resulted in satisfactory biomass levels at the end of the growing season. Including a SC reduced oat yield, but increased winter wheat yield in two-thirds of simulations. Model outputs showed that including a SC resulted in 33–79% more fresh soil organic carbon, depending on site, compared with no SC. Nitrogen (N) uptake by both crops was highest in the SC scenario. In oats, N losses did not differ between the two scenarios, while in winter wheat the SC scenario had approximately 50% lower N leaching losses and 30% higher gaseous N emissions. However, in the fallow period from winter wheat harvest through to spring, both types of N losses were elevated in the SC scenario. The SC scenario had only a minor effect on water dynamics, causing a small reduction in soil water content. In this paper we give an example of how APSIM NG can be used to assess ecosystem services from complex agricultural systems using a case study with intercropping of cereals and leguminous SCs. APSIM NG was useful in providing a holistic assessment, and we show that intercropping with a SC can improve cropping system performance and reduce negative impacts, but long-term strategic management of N is required to prevent increased losses. To further improve simulation of intercrops more accurate simulation of early growth is needed for all crops included. [Display omitted] • Crop modules for oats, winter wheat and red clover were calibrated to simulate intercrops in Sweden in APSIM NG. • Effects of intercropping cereals (oats-winter wheat) and a legume service crop on cereals and soil processes were assessed. • Calibration resulted in satisfactory end-biomass, but poor simulation of biomass during leaf development and tillering. • Intercropping with a service crop had positive effects from an ecosystem service perspective. • Drawbacks were elevated N losses in winter wheat and fallow, indicating a need for long-term N management. [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]

Abstract Catch crop (CC) mixtures of non-legumes (nL) and legumes (L) have been promoted as a strategy to achieve two different goals: to decrease the risk of nitrate leaching and to enhance the nitrogen supply to the subsequent crop. To investigate if two-component mixtures of nL + L have advantages over pure nL stands experiments were carried out over a two year period (2013–2015) at two contrasting field sites in Denmark. Nitrogen (N) uptake by the CCs was measured by aboveground biomass sampling, and N leaching by ceramic suction cups. When grown in pure stands, white clover (Trifolium repens) on coarse sand and common vetch (Vicia sativa) on sandy loam were less effective at reducing N leaching than perennial ryegrass (Lolium perenne) and fodder radish (Raphanus sativus). When the proportion of the nL + L in mixtures was similar or favored the nL, leaching was not significantly different from the nL in the pure stand. However, during one of the years on the sandy loam L (vetch) almost outperformed nL (fodder radish), resulting in N leaching from nL + L similar to L. The yield of the following spring barley was only significantly different from the yield in the plots with previously bare soil in one of the years on the coarse sandy soil. It is concluded that in nL + L mixtures L can take over and thereby lower the effect of the CCs on N leaching while not necessarily enhancing the N supply for the subsequent crop. Highlights • In monocultures legumes were less effective at reducing N leaching than non-legumes. • Non-legume/legume mixtures were as effective as non-legume catch crops in reducing N leaching. • When non-legume/legume mixtures are not balanced N leaching was similar to that from legumes. • Use a catch crop only increased the subsequent spring yield on the sandy loam in one of the years. • The catch crop had no effect on the yield of the subsequent crop on the clay soil. [ABSTRACT FROM AUTHOR]

Catch crops have been proven effective in reducing nitrogen leaching in cropping systems due to their uptake of post-harvest soil mineral N prior to the main percolation season in winter. Information on the residual effect of catch crops, and their nitrogen fertilizer replacement value is scarce. To determine nitrogen fertilizer replacement values for different catch crops a field experiment was conducted over a four-year period on a sandy soil in Denmark, involving different catch crops and catch crop mixtures with non-legume and legume species. The residual effect of the catch crops was measured in spring barley grown in the residual year. For comparison, winter rye was also included. Over the four-year period the spring barley/fodder radish showed significantly lower leaching compared with the other catch crops, and the winter rye had the highest leaching. Regarding the residual effect, fodder radish and ryegrass, were most valuable, with nitrogen fertilizer replacement values ranging from 13 to 41 kg ha-1, based on fertilizer recovery efficiency of 50%. The process based APSIM (Agricultural Production Systems sIMulator) model was used to simulate the spring barley/catch crop rotations and the winter rye, and showed good model performance regarding N leaching and, crop yield and N uptake. The model was then run over a period of 20 years, to determine variations in N leaching and residual effects due to environmental conditions. The simulations showed that catch crops reduced N leaching by 38–64% when grown every year, and by 21–39% when grown only every second year. Nitrogen fertilizer replacement values ranged on average from 28 to 44 kg N ha-1, but showed high inter-annual variability. The nitrogen fertilizer replacement values showed only a weak relationship with the N uptake of the catch crop prior to termination, likely due to long term effects of N mineralisation from catch crop residues and pre-emptive competition for N by the catch crop. • Catch crops (CCs) were effective at reducing N leaching to or below that of the reduced N fertilizer treatment. • APSIM modelling indicates nitrogen fertilizer replacement values (NFRV) of catch crops ranging from 28 to 44 kg N ha-1. • APSIM modelling indicates that volunteers can be used as a low-cost alternative to CCs. • NFRVs showed high inter-annual variability and were not related to the CCs' N uptake. [ABSTRACT FROM AUTHOR]

• Early sowing of winter cereals reduced N leaching compared with timely sowing. • Catch crops in spring barley reduced N leaching compared with bare soil. • Sowing time and catch crops did not affect grain yield or N concentration of grain. • In a wetter climate, early sown winter rye had similar N leaching as a spring barley/ryegrass. • In a drier climate, early sown winter wheat had higher leaching than spring barley/fodder radish. Sustainable management of intensively managed agricultural land requires high productivity with low environmental impacts. There is a lack of understanding concerning the effectiveness of early sowing of winter cereals compared with catch crops for reducing nitrogen (N) leaching losses. To test this, an experiment was conducted over three years (2016–2019) with different crop rotations and increasing rates of N fertilisation. The experiment was done at two contrasting sites in Denmark; one of the sites was at Foulum (FU) on a sandy loam in a wetter climate and the other at Flakkebjerg (FB) on a sandy loam soil in a drier climate. The main crops were either spring barley (SB), or winter rye (WR) at FU and winter wheat (WW) at FB. The SB received four different N fertilisation rates ranging from 0 to 200 kg N ha−1, and the winter cereals six different rates ranging from 0 to 255 for WR and from 0 to 300 kg N ha−1 for WW. In the SB treatments the soil was either left bare over winter, or sown with volunteer barley plants or catch crops. The catch crop used at FU was ryegrass, while fodder radish was used at FB. The WR and WW were either sown timely, according to common practice at the end of September or about three weeks earlier. Neither early sowing nor the use of a catch crop affected the grain yield or the grain N concentration. Nitrate leaching was reduced on both sites by early sowing and by the use of a catch crop. Early sowing of WR at FU reduced N leaching compared to timely sowing, and had almost the same N leaching as the spring barley/ryegrass rotation. At FB, early sowing of WW also reduced N leaching compared to timely sowing, but this was only significant in one of the three years, and leaching was much higher than in the spring barley/fodder radish rotation. Both early sowing of winter cereals and the use of a catch crop in spring cereals are mitigation options for reducing N leaching. [ABSTRACT FROM AUTHOR]

• A simple mineralisation model (SMM) based on first order decay and the C:N was tested. • SMM, linked with APSIM could predict N release from catch crop residues well. • The default approach in APSIM underpredicted N mineralisation from catch crops (CC). • APSIM with SMM potential tool for predicting effect of CC on N leaching and N supply. Determining the nitrogen (N) release from catch crop residues is important for N management in arable farming systems. The use of catch crops and subsequent incorporation of its residues represents a nutrient provision for the following crop and has the potential of reducing N leaching. To investigate whether the Agricultural Production Simulator (APSIM) can be used to predict the N release from Brassica catch crop residues with different carbon to nitrogen ratios (C:N) under different temperatures the model was set-up using three different approaches: (i) the generic approach, in which the residue is distributed to the various carbon pools with default APSIM parameters (Gen), (ii) the generic approach but with partitioning of the various pools based on the biochemical composition (Gen-BC), and (iii) the inclusion of an additional carbon pool in which mineralisation is based on first order decay and the C:N of the crop residue, termed simple mineralisation model (SMM). The SMM was parameterized based on results from various previous incubation studies. APSIM was then used to predict N release through mineralisation from these experiments. The simulations indicate that the generic approach in APSIM greatly underestimates the amount of N released from the cover crop residues, especially at low temperatures; the model efficiency (based on the Nash Sutcliffe efficiency score) was negative for the incubation study done at 2 °C. APSIM linked with the SMM shows a substantially higher prediction accuracy. The Gen-BC, which could only be done for one of the incubation experiments, had a higher prediction accuracy than the generic approach, but was not as good as the SMM. This indicates that, for accurate predictions of N mineralisation from Brassica catch crop residues, the generic approach with default partitioning needs to be modified, either by assigning various carbon pools based on the biochemical composition or by including an additional carbon pool. [ABSTRACT FROM AUTHOR]

Importing protein into Europe is causing sustainability challenges, which has resulted in an increasing European interest in locally growing faba bean as a protein source. There is, however, a concern that this may result in higher nitrate leaching compared with conventional cereal-based systems. We investigated the risk of nitrate leaching and its mitigation strategy after growing faba bean with catch crops within a conventional European cropping system that also includes catch crops in spring barley. We conducted a field experiment with faba bean (Vicia faba L.) and three catch crops (chicory (Cichorium intybus L.), perennial ryegrass (Lolium perenne L.) and winter rye (Secale cereale L.)) grown in sequence with spring barley (Hordeum vulgare L.) and replicated in time over a period of three years. Continuous spring barley with catch crops (perennial ryegrass and fodder radish (Raphanus sativus L.)) were used as a reference. Measurements included grain yield and grain nitrogen (N) of the main crops, aboveground biomass and N yield of the catch crops, and nitrate leaching. Grain yield and grain N of faba bean grown with undersown catch crops were not statistically different than without catch crop and post-harvest sown catch crops. Catch crops with faba bean had lower aboveground biomass and N yield than with spring barley. Faba bean as pre-crop compensated for the reduced amount of fertilizer input and also increased the grain yield and grain N of the subsequent spring barley. In 2020–21, nitrate leaching from both spring barley and faba bean without catch crops was not statistically different, with an average of 64 kg NO 3 -N ha−1. In contrast, in 2021–22, nitrate leaching after faba bean without catch crops was higher with 104 kg NO 3 -N ha−1, compared with spring barley with 68 kg NO 3 -N ha−1. Catch crops significantly reduced nitrate leaching on average by up to 55 kg NO 3 -N ha−1 from faba bean and 62 kg NO 3 -N ha−1 from spring barley fields. The study reveals that growing faba bean can reduce N fertilizer input without compromising the grain yield and grain N of following spring barley. Variable nitrate leaching between years from faba bean requires more research on diverse pedo-climatic and agronomic conditions to better assess nitrate leaching risks and reduction strategies. These results will aid in designing cropping systems including faba bean and catch crops combinations to reduce N fertilizer input and nitrate leaching risks and improve protein sufficiency. • Undersown catch crops did not affect grain yield and grain N of faba bean. • Pre-crop faba bean with or without catch crops increased grain yield and grain N of spring barley. • Compared to spring barley, nitrate leaching from faba bean was similar in one drainage period and higher in another. • Post-harvest and undersown catch crops equally reduced nitrate leaching after faba bean. • Compared to spring barley, effectiveness of catch crop with faba bean was inconsistent in different drainage periods. [ABSTRACT FROM AUTHOR]

• the superiority of arable conventional or organic crop rotations regarding N leaching depends on the functional unit used. • organic arable crop rotations reduced the nitrate leaching loads per area significantly. • production related N leaching was 50 % lower in the conventional system. • all crop rotations exceeded the critical N load with respect to the EU-Nitrate directive threshold. • integrated approaches, which include crops with high N uptake efficiency in late autumn are needed to fulfill EU standards. Sustainable intensive agriculture requires enhanced nitrogen use efficiency and reductions in nitrogen (N) leaching losses. To investigate if organic farming systems have potential to achieve this, a comparison between conventional and organic arable farming was carried out over a two-year period. Two differently managed specialized organic arable crop rotations (low N-intensive (Ol), semi -N- intensive (Os)), and a typical N-intensive conventional crop rotation (Ch) were studied. The study was done under commercial farm scale conditions covering close to 400 ha in total (5−23 ha field sizes) in a highly productive arable region on fertile soils in northern Germany. Nitrogen leaching losses were measured using ceramic suction cups. Two functional units were used as indicators for eco-efficiency: N losses per area and per unit of grain equivalent (GE) produced. Results revealed that organic arable crop rotations reduced the nitrate (NO 3 -N) leaching loads per area significantly, with losses (kg NO 3 −-N ha-1 a-1) of 22.0 in Ol, 24.4 in Os and 35.1 in Ch. In contrast, when using the functional unit 'nitrate leaching per grain equivalent' as an indicator for eco-efficiency the conventional system resulted in 50 % lower N leaching loads per GE. This was due to the much higher land use efficiency of the conventional system (115 GE ha-1 vs 36 GE ha-1 for Ol and 38 GE ha-1 for Os), which resulted in N leaching losses (kg NO 3 -N GE-1) of Ch 0.32 for Ch, 0.64 for Ol, and 0.66 for Os. Regarding EU-Nitrate directive threshold for drinking water of 11.3 mg NO 3 -N l-1, all crop rotations exceeded the critical load. For the various main crop/preceeding crop sequences, the soil mineral N content at the end of the vegetation period and the autumn N uptake were the best predictors for N leaching, whereas for the aggregated effect across the various crop rotations within a farm system the N balance was the best descriptor. Considering N leaching loads our results show that both, specialized arable conventional and organic farming systems fail to meet the requirements of given environmental standards for water protection in the EU. This suggests that integrated approaches beyond such specialised systems are necessary, which are based on a balanced combination of forages (with two year leys), catch crops and cash crops. [ABSTRACT FROM AUTHOR]