van Vugt D, Franke A C, Giller K E
Plant Production Systems, Wageningen University, PO Box 430, 6700 AT Wageningen, The Netherlands.
International Institute of Tropical Agriculture, Chitedze Research Station, PO Box 30258, Lilongwe 3, Malawi.
Agric Ecosyst Environ. 2018 Jul 1;261:241-250. doi: 10.1016/j.agee.2017.05.008.
Soybean production can contribute to the nitrogen economy of smallholder farming systems, but our understanding of factors explaining variability in nitrogen fixation and rotational benefits across farms and regions is limited. Biological nitrogen fixation (BNF) was quantified with the natural abundance method in 150 farmer-managed soybean plots under different varieties and inputs in Dowa, Mchinji and Salima districts of Malawi. Soybean yielded on average 1.2 t ha grain and the above-ground biomass at mid pod filling (R5.5) was 2.8 t ha and contained in total 63 kg ha nitrogen derived from the atmosphere (Ndfa). Locally sourced varieties obtained a larger %Ndfa (65%) than the 'improved' variety Nasoko (53%). The %Ndfa was positively associated with soil sand content, sowing date, plant population and biomass accumulation, but it was not affected by inoculation with rhizobia or the combination of inoculation and NPK fertiliser application. Quantities of N fixed differed between regions and years, and was enhanced by applying inoculant and fertiliser together, leading to more biomass accumulation and larger grain yields. Soil available P and exchangeable K contents also increased the total amount of N fixed. In a related trial, continuous maize yields were compared with maize following soybean in 53 farmer-managed fields. Average yield in continuous maize was 2.5 t ha, while maize after soybean produced 3.5 t ha (139% of continuous maize). Farmers with higher maize yields, who applied external nutrient inputs, and with a larger value of household assets achieved greater yield responses to rotation with soybean. A relative yield increase of more than 10% was observed on 59, 90 and 77% of the fields in Dowa, Mchinji and Salima respectively. We conclude that fields of soybean and maize that receive adequate nutrient inputs and good management to ensure good yields benefit most in terms of quantities of N fixed by the legume and the yield response of the following maize crop. The results suggest that the promotion of soybean-maize rotations should be done through an integrated approach including the promotion of appropriate soil and crop management techniques. Furthermore, they suggest that wealthier households are more likely to apply adequate nutrient inputs and good crop management practices and are likely to receive larger maize yield responses to the incorporation of soybean.
大豆生产有助于小农种植系统的氮素循环，但我们对解释不同农场和地区间固氮作用及轮作效益差异的因素的了解有限。在马拉维的多瓦、姆钦吉和萨利马地区，采用自然丰度法对150个由农民管理的、种植不同品种大豆并采用不同投入方式的地块中的生物固氮作用进行了量化。大豆平均每公顷产粮1.2吨，结荚中期（R5.5）地上生物量为每公顷2.8吨，地上生物量中源自大气的氮总量（Ndfa）为每公顷63千克。当地品种的Ndfa占比（65%）高于“改良”品种纳索科（53%）。Ndfa占比与土壤含砂量、播种日期、种植密度和生物量积累呈正相关，但不受根瘤菌接种或接种与氮磷钾施肥组合的影响。不同地区和年份的固氮量有所不同，同时施用接种剂和肥料可提高固氮量，从而增加生物量积累并提高粮食产量。土壤有效磷和交换性钾含量也会增加总固氮量。在一项相关试验中，对53个由农民管理的地块上的连作玉米产量与大豆后作玉米产量进行了比较。连作玉米平均产量为每公顷2.5吨，而大豆后作玉米产量为每公顷3.5吨（连作玉米产量的139%）。施用外部养分投入且家庭资产价值较高、玉米产量较高的农户从与大豆轮作中获得的产量增幅更大。在多瓦、姆钦吉和萨利马地区，分别有59%、90%和77%的地块相对产量增幅超过10%。我们得出结论，大豆和玉米地块若能获得充足养分投入并进行良好管理以确保高产，则在豆类作物的固氮量以及后作玉米的产量响应方面受益最大。结果表明，推广大豆 - 玉米轮作应采用综合方法，包括推广适当的土壤和作物管理技术。此外，结果还表明，较富裕的家庭更有可能施用充足的养分投入并采用良好的作物管理措施，且在将大豆纳入轮作后，玉米产量可能会有更大增幅。
