Rye and grass cover crops can potentially intercept residual soil mineral nitrogen (SMN), reduce overwinter leaching, transfer SMN to next growing seasons and reduce the fertilizer need of subsequent crops. These aspects were studied for 6 years in continuous silage maize cv. LG 2080 production systems receiving 20-304 kg N/ha, on a sandy soil in the Netherlands. Rye cv. Admiraal and grass (Lolium multiflorum cv. Combita) cover crops were able to absorb on average 40 kg N/ha into the shoots. The actual N uptake was largely determined by winter temperatures and hardly affected by residual SMN. At low N input levels cover crops reduced N leaching in accordance with their N uptake. At high N input levels, however, the reduction of leaching losses exceeded the storage capacity of the cover crop, suggesting that cover cropping stimulated the loss of N via denitrification or immobilization. Cover crops had no positive effect on maize yields at larger N rates and under these conditions cover crops did not improve the conversion of SMN into crop N. This was only partly reflected by an increase of residual SMN on plots where cover crops had been incorporated, as a large part of the excess N applied to maize was already lost during the growing season. In N-deficient maize production systems, however, cover crops increased the dry matter yield of maize. Their effect was equivalent to the effect of fertilizer N rates amounting to 105 and 44% of the shoot N in rye and L. multiflorum, respectively. In the first few years cover crops decomposed incompletely during the growing season following their incorporation. In the course of the years, however, effects on subsequent maize crops increased. This supports the hypothesis that the effects of cover crops are cumulative when grown repeatedly. Averaged over the 6 years, 115% and 73% of the shoot rye N and L. multiflorum N, respectively, were recovered in the crop-soil system.
In this report we present a model toolbox consisting of the Bio-Economic Farm Models (BEFMs) DairyWise and Farmdyn together with tools that focus on specific farm management aspects to analyse integrated aspects of circular agriculture at farm level. Based on a conceptual model regarding relevant policy questions, indicators and model requirements, knowledge and modelling gaps are pointed at. It is concluded that combined model use can overcome part of the modelling gaps, but not all. The combined model use is demonstrated analysing the impact of a tax on chemical fertiliser on a dairy farm on sandy soil and an arable farm on clay soil. The report ends with recommendations regarding research directions in the field of modelling circular agriculture aspects at farm level, sharing and harmonising key modules and investments in quality and quantity of different networks of model developers and users. We also give recommendations for researchers and modelers who are looking for possibilities of combined model use.
In 1991-94 the effects of subsurface band application of mineral N fertilizer on the N recovery and dry matter (DM) yield of silage maize were studied in nine field experiments on sandy and clay soils in the Netherlands. In the early crop stages and especially in the clay soil experiments, banded N had a significant negative effect on the N uptake and DM yield compared to broadcast N, possibly due to salt damage. At final harvest, however, banding significantly increased the N uptake and DM yield in most of the experiments. The apparent N recovery increased by circa 20-25% (absolute). The positive effects indicated that band application improved the efficiency of the N fertilizer. It could be calculated that banding allowed a reduction in the N rate of 20-30% without significant effects on the N uptake and DM yield of the silage maize. Benefits of banding were positively (P
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