After 20 years of application of different manure types, cropping systems and additional nitrogen (N) levels, their residual fertility effects were compared by measuring the yield of a following unfertilised wheat crop (Experiment 1), which was sown on exactly the same plots of the previous long-term trial. All previously applied factors caused significant differences in wheat yield. Wheat yielded more on plots that had received farmyard manure (FMY) compared to those where semi-liquid manure (SLM) was previously applied. Long-term application of a semi-intensive rotation, with three years of annual double cropping of autumnsown Italian ryegrass and spring-sown silage maize followed by three years of mown lucerne (R6), resulted in higher wheat yield than application of just the annual double cropping of Italian ryegrass and silage maize (R1). Application of further mineral N fertilisation to previous cropping systems caused higher yield of the subsequent wheat crop. The difference in wheat yield between the R6 and R1 systems was greater with SLM (+28%) than FYM application (+11%) resulting in a significant manure × system interaction. A companion experiment (Experiment 2) was carried out to compute the nitrogen agronomic efficiency (NAE) from the yield of wheat plots that were sown after ploughing a nearby 20- year unfertilised grassland and received four levels of mineral N fertilisation. NAE was further used to empirically estimate the productive advantage (PA) conferred by previous manure-systemmineral nitrogen combinations in the long-term trial. PA was measured as equivalent kg of mineral N to be applied to wheat to achieve the yield level recorded after any previous combination. The estimated PA values were much higher when wheat followed FYM compared to SLM application, and when it followed R6 compared to R1 system. The SLM-R1 combination had negative PA values, indicating a productive disadvantage on wheat of this preceding combination. The enhancement of residual soil fertility by long-term application of FYM compared to SLM could be attributed to greater nutrient provision during the years by FYM than by SLM. However, further fertility advantages of FYM are discussed. Despite lower nutrient supply by organic fertilisers in R6 than in R1 system, the former had higher residual fertility. The presence of lucerne in the R6 rotation likely enriched the soil in nitrogen and increased its availability for following cropping. Possible benefits of the legume on the soil suppressiveness might have been a further asset of the R6 system.

中文翻译：

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在意大利北部采用不同粪便管理的牧草种植系统 20 年后，小麦产量作为剩余肥力的衡量标准

在施用不同的肥料类型、耕作制度和额外的氮 (N) 水平 20 年后，通过测量随后未施肥的小麦作物（实验 1）的产量来比较它们的剩余肥力效应，该作物播种在完全相同的地块上之前的长期试验。所有以前应用的因素都导致小麦产量的显着差异。与之前施用半液体肥料 (SLM) 的地块相比，接受过农家肥 (FMY) 的地块的小麦产量更高。长期应用半集约化轮作，秋播意大利黑麦草和春播青贮玉米三年双熟，然后三年割苜蓿 (R6)，导致小麦产量高于仅施用一年生作物意大利黑麦草和青贮玉米 (R1) 的双作。在先前的种植系统中进一步施用矿物氮肥可提高后续小麦作物的产量。R6 和 R1 系统之间小麦产量的差异使用 SLM (+28%) 大于 FYM 应用 (+11%)，导致显着的粪便 × 系统相互作用。进行了一项配套实验（实验 2），根据在耕种附近 20 年未施肥的草地后播种的小麦地块的产量计算氮农学效率 (NAE)，并接受了四种水平的矿物氮肥。NAE 进一步用于经验性地估计长期试验中先前粪便-系统矿物氮组合赋予的生产优势 (PA)。PA 被测量为等量公斤的矿物质 N，用于小麦以达到任何先前组合后记录的产量水平。与 SLM 应用相比，小麦遵循 FYM 时的估计 PA 值要高得多，与 R6 相比，当它遵循 R6 时。SLM-R1 组合的 PA 值为负，表明该组合对小麦的生产不利。与 SLM 相比，长期施用 FYM 可提高土壤残余肥力，这可归因于 FYM 比 SLM 在这些年中提供的养分更多。然而，讨论了 FYM 的进一步生育优势。尽管 R6 有机肥的养分供应低于 R1 系统，但前者具有更高的剩余肥力。R6 轮作中苜蓿的存在可能丰富了土壤中的氮，并增加了其可用于后续种植。