Franke A C, van den Brand G J, Vanlauwe B, Giller K E
Soil, Crop and Climate Sciences, University of the Free State, PO Box 339, Bloemfontein 9300, South Africa.
Plant Production Systems, Wageningen University, PO Box 430, 6700 AK Wageningen, The Netherlands.
Agric Ecosyst Environ. 2018 Jul 1;261:172-185. doi: 10.1016/j.agee.2017.09.029.
We conducted a systematic review of literature on the residual effects of grain legumes in cereal-based systems of sub-Saharan Africa (SSA) to quantify the magnitude and variability of rotational effects, to explore the importance of environmental and management factors in determining variability and to evaluate the evidence of the different mechanisms that explain rotational effects. We retrieved 44 unique publications providing 199 observations comparing continuous cereal performance with that of a grain legume-cereal rotation. The overall mean yield increase of 0.49 t grain ha, equal to an increase of 41% of the continuous cereal yield, is highly significant, but the variability in residual effects is large. Effects were more pronounced in southern Africa, the highlands of East Africa and the Guinea savannah, and less in the humid forest/derived savannah of West Africa and the Sudano-Sahelian zone. Maize showed stronger yield responses after a legume than millet and sorghum. Agro-ecological zone and cereal type were however confounded. All grain legume types significantly improved cereal yields, with stronger residual effects observed after soybean and groundnut than after cowpea. Fertiliser N application to cereals reduces the residual effects of legumes, but the response at 60-120 kg N ha still equalled 0.32 t ha or 59% of the response when no N is applied. The sustained benefits with large N applications indicate the importance of non-N effects. While mechanisms for improved soil P availability after grain legumes have been studied in some detail, it remains uncertain how important these are in farmers' fields. Grain legumes are unlikely to have a major influence on the availability of nutrients other than N and P, or on soil pH. Beneficial impacts of grain legumes on soil organic matter content can occur if legumes contribute to a greater overall cropping productivity, but studies generally report no such impacts. Evidence of impacts of grain legumes on weeds is limited to striga. Studies on the impacts on nematode pressure in cereals are inconclusive, probably because legumes act as a host for some of the key nematode genera that harm maize. The impact on the pressure of other pests and diseases in cereals is probably important, but evidence on this from SSA is lacking. Future research on N-fixation by grain legumes and residual N benefits should focus on explaining the wide variability observed among sites. There is a clear need for more detailed mechanistic studies to assess the occurrence and relevance of non-N effects of grain legumes, particularly in relation to common pests and diseases in cereals.
我们对撒哈拉以南非洲（SSA）以谷物为基础的系统中豆类作物残留效应的文献进行了系统综述，以量化轮作效应的大小和变异性，探讨环境和管理因素在决定变异性方面的重要性，并评估解释轮作效应的不同机制的证据。我们检索到44篇独特的出版物，提供了199项观察结果，比较了连续种植谷物的表现与豆类-谷物轮作的表现。谷物总产量平均增加0.49吨/公顷，相当于连续种植谷物产量增加41%，这一增幅非常显著，但残留效应的变异性很大。在南部非洲、东非高地和几内亚稀树草原，效应更为明显，而在西非湿润森林/次生稀树草原和苏丹-萨赫勒地区则较小。与小米和高粱相比，玉米在种植豆类后产量反应更强。然而，农业生态区和谷物类型存在混淆。所有豆类作物类型均显著提高了谷物产量，大豆和花生后的残留效应比豇豆更强。对谷物施用氮肥会降低豆类的残留效应，但每公顷施用60-120公斤氮肥时的产量反应仍相当于0.32吨/公顷，或不施氮肥时产量反应的59%。大量施用氮肥带来的持续益处表明了非氮效应的重要性。虽然已经对豆类作物种植后土壤磷有效性提高的机制进行了一些详细研究，但这些机制在农民田间的重要性仍不确定。豆类作物对除氮和磷以外的其他养分有效性以及土壤pH值的影响可能不大。如果豆类作物有助于提高整体作物生产力，那么它们对土壤有机质含量可能会产生有益影响，但研究普遍报告没有此类影响。豆类作物对杂草影响的证据仅限于独脚金。关于豆类作物对谷物中线虫压力影响的研究尚无定论，可能是因为豆类是一些危害玉米的关键线虫属的寄主。豆类作物对谷物中其他病虫害压力的影响可能很重要，但SSA缺乏这方面的证据。未来关于豆类作物固氮和残留氮益处的研究应侧重于解释不同地点观察到的广泛变异性。显然需要进行更详细的机理研究，以评估豆类作物非氮效应的发生情况及其相关性，特别是与谷物常见病虫害相关的情况。
