In response to the extensive development of upland rice on the hillsides of the Malagasy highlands, alternative cropping systems have been designed based on conservation agriculture (CA). As the promotion of CA in smallholder farming systems is still the subject of debate, its potential benefits for smallholder farmers require further assessment. In the context of resource-poor farmers and low-input production systems, nitrogen (N) is a major limiting nutrient. The effects of contrasted cropping systems have been studied on upland rice yield and N uptake in rainfed conditions: conventional tillage (CT) and CA with a mulch of maize or a legume (Stylosanthes or velvet bean). Decision Support Systems for Agrotechnology Transfer (DSSAT) crop growth model was used to quantify the soil N balance according to the season and the cropping system. The lowest yields were obtained in CA with a mulch of maize and were also associated with the lowest crop N uptake. Upland rice yields were higher or equivalent under CA with a legume mulch than under CT cropping systems. The supply of N was considerably higher in CA with a legume mulch than in CT, but due to higher leaching and immobilization in CA, the final contribution of N from the mulch to the crop was reduced although not negligible. DSSAT has been shown to be sufficiently robust and flexible to simulate the soil N balance in contrasting cropping systems. The challenge is now to evaluate the model in less contrasted experimental conditions in order to validate its use for N uptake and yield prediction in support to the optimization and design of new cropping systems.

中文翻译：

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对比种植制度对马达加斯加旱稻产量和氮平衡的影响：来自 DSSAT 模型的输入

为了应对马达加斯加高地山坡上旱稻的广泛开发，人们设计了基于保护性农业 (CA) 的替代种植系统。由于在小农户农业系统中推广 CA 仍然是争论的主题，它对小农户的潜在好处需要进一步评估。在资源贫乏的农民和低投入生产系统的背景下，氮 (N) 是主要的限制性营养素。在雨养条件下研究了对比种植系统对旱稻产量和氮吸收的影响：常规耕作 (CT) 和覆盖玉米或豆科植物（柱花草或丝绒豆）的 CA。农业技术转让决策支持系统 (DSSAT) 作物生长模型用于根据季节和种植系统量化土壤氮平衡。覆盖玉米的 CA 产量最低，并且与作物 N 吸收量最低有关。使用豆科植物覆盖的 CA 与 CT 种植系统相比，陆地水稻的产量更高或相当。使用豆科植物覆盖物的 CA 中的 N 供应量明显高于 CT，但由于 CA 中较高的浸出和固定化，N 从覆盖物对作物的最终贡献减少，尽管不可忽略不计。DSSAT 已被证明具有足够的鲁棒性和灵活性来模拟对比种植系统中的土壤 N 平衡。现在的挑战是在对比较少的实验条件下评估该模型，以验证其在氮吸收和产量预测方面的用途，以支持新种植系统的优化和设计。