Results are reported from 57 N-fertilizer trials with spring cereals on various soils in SE Norway during the period 1991-95. Grain yields and nitrogen uptake were compared at fertilizer levels both above and below those used by the farmers on whose land the trials were located, and apparent N-fertilizer recovery was calculated as a percentage of that applied. Current fertilizer practice was close to the recommended levels. Grain yields increased by an average of 40-220 kg/ha (1-4%) when fertilizer levels were raised by 15-45 kg N/ha, relative to current farming practice, whereas a similar lowering of fertilizer rates reduced grain yields by 160-600 kg/ha (3-11%). Protein concentration and N-uptake in grain increased almost linearly with increasing levels of N-fertilizer, but apparent recoveries nevertheless declined in most cases with increasing N-fertilizer. Recoveries were greatest (approx. 45-60%) on loam soil and in wheat, and lowest (approx. 30-45%) on clay soils and in barley. A balance between N removed in the grain crop and that supplied as fertilizer was achieved at N-fertilizer rates that were lower than, those used in current farmer practice, by amounts ranging from about 15 kg N/ha on loam soil and in wheat to around 45 kg N/ ha on silt and clay soils and in barley. Current practice gives a closer balance when N in straw is also taken into account, assuming complete removal of straw from the system. Calculation of N-balance at different yield levels revealed that current fertilizer recommendations give a fertilizer surplus of 10-30 kg N/ha when straw is retained, but a slight shortfall in nitrogen supply at medium to high yield levels when straw is removed. In a series of 12 trials it was demonstrated that about 25% of total N-fertilizer can be applied at heading without yield loss and with a slight increase in protein concentration. Levels of soil mineral-N measured in spring were positively correlated with yields and N-uptakes on unfertilized plots, but had little effect on the optimum fertilizer levels found in individual trials.
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机译：在1991-95年间，挪威东南部的57种氮肥在春季土壤上的氮肥试验报告了结果。比较了试验所在土地上农民使用的肥料水平上和下的肥料水平下的粮食产量和氮素吸收量，并计算了表观氮肥回收率（以施用量的百分比）。当前的肥料操作已接近建议水平。相对于当前的耕作方式，当肥料水平提高15-45 kg N / ha时，谷物平均增产40-220 kg / ha（1-4％），而肥料水平的类似降低降低了谷物产量。 160-600公斤/公顷（3-11％）。籽粒中蛋白质的浓度和氮的吸收量随氮肥水平的增加而呈线性增加，但是在大多数情况下，随着氮肥含量的增加，表观的回收率却下降了。在壤土和小麦上的回收率最高（约45-60％），在黏土和大麦上的回收率最低（约30-45％）。在谷物作物中去除的氮与作为肥料供应的氮之间的平衡要以低于当前农民实践中所使用的氮肥的比例达到，其量在壤土和小麦上约为15千克氮/公顷，在淤泥和黏土以及大麦上大约为45 kg N / ha。假设将秸秆从系统中完全清除，当前的做法还考虑了秸秆中的氮，从而提供了更紧密的平衡。通过计算不同产量水平下的氮平衡，可以发现，当保留秸秆时，当前的化肥建议可提供10-30 kg N / ha的肥料过剩，但是当中度秸秆移至高产量水平时，氮素供应略有不足。在一系列的12个试验中，事实证明，抽穗期可以施用总氮肥的约25％，而不会造成产量损失且蛋白质浓度略有增加。春季测得的土壤矿质氮水平与未施肥田地的产量和氮素吸收呈正相关，但对个别试验中发现的最佳肥料水平影响不大。
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