Roobroeck Dries, Palm Cheryl A, Nziguheba Generose, Weil Ray, Vanlauwe Bernard
International Institute of Tropical Agriculture, c/o ICIPE, Kasarani, P.O. Box 30772-00100, Nairobi, Kenya.
University of Florida, P.O. Box 110570, Gainesville, FL32611, USA.
Agric Ecosyst Environ. 2021 Jan 1;305:107165. doi: 10.1016/j.agee.2020.107165.
Use of mineral fertilizers is essential to enhance crop productivity in smallholder farming systems of Sub-Saharan Africa, but various studies have reported 'non-responsiveness' where application of inorganic fertilizers does not lead to satisfactory yield gains. This phenomenon is not well defined nor are its extent and causes well understood. In order to close these knowledge gaps, we assessed the effects of commonly recommended nitrogen (N), phosphorus (P) and/or potassium (K) fertilizer inputs on maize grain and soybean production on farmer fields across prevalent land slope and/or soil texture gradients (2 × 2 matrix) in four agroecosystems over two growing seasons. The extent of the problem in the two cropping systems was compared by decomposing frequency distributions into various ranges of fertilizer effect sizes that represent specific degrees of non-responsiveness and responsiveness. Key soil properties and rainfall variables for field trials were also determined to identify the factors that are limiting crop yield increases by mineral fertilizer input. Significant differences were found in mean fertilizer effect on crop productivity and frequency of non-responsiveness among the study areas and growing seasons, with some explicit contrasts between maize and soybean. The application of mineral fertilizers failed to increase maize yields by more than 0.5 t ha in up to 68 % of farmer fields and soybean yields by more than 150 kg ha in up to 65 % of farmer fields for specific study areas and/or growing seasons, while for others crop responses exceeded those levels. Unlike hypothesized, there were no consistent differences in crop fertilizer responses between the soil texture and land slope classes at any of the study sites. The variation in fertilizer effects on maize grain productivity across the study areas and growing seasons was most strongly related to the soil silt and clay content, and exchangeable cation balances of calcium (Ca), magnesium (Mg) and K, whereas fertilizer effects on soybean were most strongly influenced by the evenness in rainfall during growing seasons, and the soil silt content, extractable P, and ratio of total C and total N. Findings from our study emphasize that non-responsiveness by maize and soybean crops in African smallholder agroecosystems is dependent on multiple interacting factors, and requires careful scrutiny to ensure returns on investments.
在撒哈拉以南非洲的小农农业系统中，使用矿物肥料对于提高作物产量至关重要，但各种研究报告了“无响应”情况，即无机肥料的施用并未带来令人满意的产量增加。这种现象的定义并不明确，其程度和原因也未得到充分理解。为了填补这些知识空白，我们在两个生长季节里，评估了在四个农业生态系统中，常见的推荐氮（N）、磷（P）和/或钾（K）肥料投入对不同土地坡度和/或土壤质地梯度（2×2矩阵）的农田中玉米籽粒和大豆产量的影响。通过将频率分布分解为代表特定无响应和响应程度的各种肥料效应大小范围，比较了两种种植系统中该问题的程度。还确定了田间试验的关键土壤特性和降雨变量，以识别限制矿物肥料投入提高作物产量的因素。在研究区域和生长季节之间，发现肥料对作物生产力的平均效应以及无响应频率存在显著差异，玉米和大豆之间存在一些明显对比。在特定研究区域和/或生长季节，高达68%的农田中，矿物肥料的施用未能使玉米产量每公顷增加超过0.5吨，高达65%的农田中，大豆产量每公顷增加超过150公斤，而在其他农田中，作物的响应超过了这些水平。与假设不同的是，在任何研究地点，土壤质地和土地坡度类别之间的作物肥料响应没有一致的差异。研究区域和生长季节中，肥料对玉米籽粒生产力的影响变化与土壤粉砂和粘土含量以及钙（Ca）、镁（Mg）和钾的交换性阳离子平衡最密切相关，而肥料对大豆的影响则受生长季节降雨均匀度、土壤粉砂含量、可提取磷以及总碳与总氮比率的影响最大。我们的研究结果强调，非洲小农农业生态系统中玉米和大豆作物的无响应情况取决于多种相互作用的因素，需要仔细审查以确保投资回报。
