ABSTRACT In the Vakinankaratra region of the Malagasy Highlands, rainfed rice cultivation has developed rapidly, which has led to rapid degradation of soil fertility and reduced productivity. This study involved a comparison of rainfed rice in rotation with maize/Brachiaria (MZ-BR) or maize/soybean (MZ-SB) intercrops, managed by direct seeding (DS) or plowed with residue burial (PB) with conventional mineral fertilization (FM) or without fertilizer (F0). The umbric Acrisol (hyperdystric) presented an anion exchange capacity (AEC) and variable charge according to the pH. Mineralizable nitrogen (Nminz.) values decreased sharply from the surface to the deep horizons and became almost nil in the 90–120 cm horizon, while the Nminz. contents of the DS treatments were systematically 5–7% higher than the PB treatment values for a given depth. The AEC of the 0–10 cm horizon was practically zero but increased significantly with depth and reached 2.58 cmol(c) kg−1. AEC values were inversely correlated with the organic carbon (Corg.) content: AEC = 1.81–0.375 Corg. The nitrate adsorption isotherms were linear and the nitrate partition coefficients (coef_nit) were correlated with the AEC values: coef_nit = 0.3363 AEC+0.1855 (R2 = 0.954). The soil nitrate stock determinants were highlighted by the matrix of correlations of the principal component analysis: excheangeable acidity and aluminum, cation exchange capacity, ΔpH, Corg. and clay and total silt contents were particularly important for the AEC and coef_nit. The different cropping systems showed no significant impact after 12 years on soil characteristics that could improve nitrogen bioavailability. We thus recommend using organic fertilization to raise the soil pH, Corg. content and nitrogen bioavailability.

中文翻译：

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可变电荷土壤的地球化学性质解释了低氮生物利用度

摘要 在马达加斯加高原的瓦基南卡拉特拉地区，雨育水稻种植发展迅速，导致土壤肥力迅速下降，生产力下降。本研究比较了轮作雨育水稻与玉米 / 臂膀 (MZ-BR) 或玉米 / 大豆 (MZ-SB) 间作，通过直播 (DS) 管理或用常规矿物施肥进行残埋 (PB) 耕作。 FM) 或不施肥 (F0)。脐带 Acrisol (hyperdystric) 根据 pH 值呈现出阴离子交换容量 (AEC) 和可变电荷。可矿化氮 (Nminz.) 值从地表到深层急剧下降，在 90-120 cm 层几乎为零，而 Nminz. DS 处理的含量系统地比给定深度的 PB 处理值高 5-7%。0-10 cm 地平线的 AEC 几乎为零，但随着深度显着增加，达到 2.58 cmol(c) kg−1。AEC 值与有机碳 (Corg.) 含量呈负相关：AEC = 1.81–0.375 Corg。硝酸盐吸附等温线是线性的，硝酸盐分配系数 (coef_nit) 与 AEC 值相关：coef_nit = 0.3363 AEC+0.1855 (R2 = 0.954)。主要成分分析的相关性矩阵突出了土壤硝酸盐储量的决定因素：可交换的酸度和铝、阳离子交换容量、ΔpH、Corg。粘土和总粉砂含量对 AEC 和 coef_nit 尤为重要。12 年后，不同的种植系统对可以提高氮生物有效性的土壤特性没有显着影响。因此，我们建议使用有机施肥来提高土壤 pH 值 Corg。含量和氮的生物利用度。