Crop Response to Gypsum Application to Subtropical Soils Under No-Till in Brazil: a Systematic Review

ABSTRACT The use of gypsum to improve the root environment in tropical soils in the southeastern and central-western regions of Brazil is a widespread practice with well-established recommendation criteria. However, only recently gypsum began to be used on subtropical soils in South of Brazil, so available knowledge of its effect on crop yield is incipient and mainly for soils under no-till (NT) systems. Avaiable studies span a wide range of responses, from a substantial increase to a slight reduction in crop yield. Also, the specific conditions leading to a favorable effect of gypsum application on crop yield are yet to be accurately identified. The primary objectives of this study were to examine previously reported results to assess the likelihood of a crop response to gypsum and to develop useful recommendation criteria for gypsum application to subtropical soils under NT in Brazil. For this purpose, we examined the results of a total of 73 growing seasons, reported in 20 different scientific publications that assessed grain yield as a function of gypsum rates. Four different scenarios were examined, by the occurrence or not of high subsurface acidity (viz., Al saturation >20 % and/or exchangeable Ca <0.5 cmolc dm-3 in the 0.20-0.40 m soil layer) and of water deficiency during the crop cycle. Based on the results, for grasses, 10 % Al saturation and/or 3 cmolc dm-3 exchangeable Ca in the soil subsurface layer (0.20-0.40 m) is more suitable than the current recommendation (Al saturation of 20 % and/or 0.5 cmolc dm-3 Ca) for subtropical NT soils in Brazil. Also, applying gypsum to NT soils with low subsurface acidity (Al saturation <10 %) and with an adequate Ca content (>3 cmolc dm-3) failed to increase crop yield, irrespective of the soil water status. Under these conditions, high gypsum rates (6-15 Mg ha−1) may even reduce grain yield, possibly by inducing K and Mg deficiency. On the other hand, applying gypsum to soils with high subsurface acidity increased yield by 16 % in corn (87 % of cases) and by 19 % in winter cereals (83 % of cases), whether or not the soil was water-deficient. By contrast, soybean yield was only increased by gypsum applied in the simultaneous presence of high soil subsurface acidity and water deficiency (average increase 27 %, 100 % of cases).

摘要 在巴西东南部与中西部地区，利用石膏（gypsum）改良热带土壤根际环境已是应用广泛且标准成熟的推荐农艺措施。然而直至近年，石膏才开始应用于巴西南部的亚热带土壤，当前关于其对作物产量影响的相关研究尚处起步阶段，且大多聚焦于免耕（no-till, NT）体系下的土壤。现有相关研究的结果差异显著，作物产量可呈现从大幅提升到小幅下降的各类响应；此外，能够明确促进石膏施用增产效果的具体条件仍有待精准探明。本研究的核心目标为梳理已发表的相关研究结果，评估作物对石膏施用产生响应的可能性，并针对巴西免耕体系下的亚热带土壤，制定具备实用价值的石膏施用推荐标准。为此，本研究整合了来自20篇不同科学出版物的共计73个生长季的试验数据，这些研究均以石膏施用量为自变量，评估其对谷物产量的影响。研究通过土壤地下高酸度（即0.20~0.40 m土层中铝饱和度＞20%和/或交换性钙＜0.5 cmolc dm⁻³）与作物生育期水分亏缺这两个因素的有无，共设置4种不同场景开展分析。基于分析结果，针对巴西亚热带免耕土壤，将0.20~0.40 m土层的铝饱和度阈值设为10%和/或交换性钙阈值设为3 cmolc dm⁻³，相较当前推荐的20%铝饱和度和/或0.5 cmolc dm⁻³交换性钙的标准更为适配。此外，若免耕土壤的地下酸度较低（铝饱和度＜10%）且钙含量充足（＞3 cmolc dm⁻³），此时施用石膏无法提升作物产量；且无论土壤水分状况如何，高施用量（6~15 Mg ha⁻¹）的石膏甚至可能诱发钾、镁元素缺乏，进而降低谷物产量。另一方面，针对地下高酸度的土壤施用石膏，可使玉米产量提升16%（有效案例占比87%），使冬季谷类作物产量提升19%（有效案例占比83%），无论土壤是否存在水分亏缺。与之形成对比的是，仅当土壤同时存在高地下酸度与水分亏缺时，施用石膏方可提升大豆产量，平均增产幅度达27%，且所有相关案例均呈现增产效果。