On upland soils in tropical Africa, common production constraints of rice and maize on smallholder farms are poor soil fertility—resulting from soil erosion and nutrient depletion—and infestation by witchweeds (Striga spp.). In Madagascar where these crops are often grown in rotation, combining legume cover crops with no-till and crop residue mulching—labelled conservation agriculture (CA)—may address these problems. Previously, it was shown that CA practices contribute to steep reductions in Striga asiatica infection. In the current study, a 4-year field experiment was conducted to test, for the first time, the hypothesis that CA practices also contribute to crop yield and soil improvements under Striga-infested conditions. The conventional mono-crop rice–maize rotation practice, involving seasonal tillage and crop residue removal, was compared to three rice–maize rotation systems following CA practices, each with a different legume cover crop option: (1) two short-cycle annual species, cowpea (Vigna unguiculata) and mucuna (Mucuna pruriens); (2) a long-cycle annual, ricebean (Vigna umbellata); and (3) a perennial, stylosanthes (S. guianensis). Rice yields, as well as yield variability, generally increased by changing from the conventional to a CA practice, and maize yields were variable and low in particular under the CA practices. CA practices significantly reduced soil displacement by rainwater runoff and increased soil nitrogen and pH levels (0–20 cm depth), in particular with stylosanthes as cover crop, but did not result in a significant change in soil organic carbon concentration. Rice yields correlated negatively with Striga asiatica plant numbers in years with moderate infection levels. This is the first study that shows mixed outcomes from CA practices in tropical cereal rotation systems on degraded, Striga-infested soils, and subsequent entry points for system improvements. Suggested improvements include judicious cover crop management, complementary fertilizer applications and selection of competitive, resistant and adapted crop varieties.

中文翻译：

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马达加斯加的低投入稻谷玉米系统对土壤和Striga保护措施的结果混杂不佳

在热带非洲的高地土壤上，小农户稻米和玉米的普遍生产限制是土壤肥力差（由于土壤侵蚀和养分消耗而造成）以及金缕梅的侵染（Striga spp。）。在马达加斯加，这些作物通常轮作种植，将豆类覆盖作物与免耕和农作物残茬覆盖物结合使用（标记为保护性农业（CA））可以解决这些问题。以前的研究表明，CA的做法有助于大大减少亚洲Striga感染。在目前的研究中，我们进行了为期4年的田间试验，以首次验证在特里加（Striga-）条件下，CA做法也有助于作物产量和土壤改良的假设。受感染的条件。将传统的单季稻－玉米轮作方法（涉及季节性耕作和作物残渣清除）与遵循CA做法的三种稻－玉米轮作系统进行了比较，每种系统都有不同的豆科作物覆盖选择：（1）两种短周期一年生品种，cow豆（Vigna unguiculata）和mucuna（Mucuna pruriens）；（2）多年生的一年生水稻（Vigna umbellata）；和（3）多年生的花序花（S. guianensis）。通过从常规方式改为CA方式，通常会增加水稻的产量以及单产的波动性，而玉米的产量则是可变的，尤其是在CA方式下较低。CA做法显着减少了雨水径流引起的土壤置换，并增加了土壤氮和pH值水平（0至20 cm深度），特别是使用苯乙烯粉作为覆盖作物，但并未导致土壤有机碳浓度发生显着变化。在中等感染水平的年份中，水稻产量与亚洲Strigaasiatica植物数量呈负相关。这是第一项研究，显示了热带谷物轮作系统中退化的斯特里加地区CA做法的混合结果-感染土壤，以及随后的系统改良入口点。建议的改进措施包括明智地进行覆盖作物管理，补充肥料以及选择具有竞争性，抗性和适应性的作物品种。