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Soil organic matter plays an important role in soil quality. In sandy soils of tropical regions, high biological activity in the soil accelerates mineralization and limits increases in organic matter content. The objective of this study was to evaluate the total organic C stock and the chemical and physical fractions of organic C in a sandy soil in Presidente Bernardes, São Paulo, Brazil, as a function of cover cropping with different combinations of grasses and legumes between 2015 and 2020. The treatments comprised fallow (control), cultivation of a single grass or intercropping of two grasses, one grass and one legume, or a mixture of two grasses and one legume during the offseason (April-September). Intercropping two grasses increased total dry matter production (shoot and root) by 138% and decreased the C/N ratio by 19% compared with the fallow and legume systems. The organic C stock in the soil was 46% higher in the mixed cover crop system (36.5 Mg ha −1 ) than in the fallow system (25 Mg ha −1 ). Humic acid (0.78-0.82 g kg −1 ) and humin (1.68-1.99 g kg −1 ) were lower in the systems with low dry matter production (fallow and grass + legume). Mineral-associated C content was 114% higher in the mixed cover crop system than in the fallow system. These results show that cover crops can increase C content in all fractions of organic matter in tropical sandy soil, even in a short period of time (5 yr), and that a mix of cover crops is the best option.

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O Estado de São Paulo é o principal produtor nacional de amendoim, e a produção está localizada principalmente na região de Jaboticabal, Tupã e Presidente Prudente. O objetivo desse estudo foi avaliar a produtividade de cultivares de amendoim em ambiente de solo arenoso no Oeste de São Paulo. O delineamento experimental foi feito em blocos ao acaso, com quatro repetições. Os tratamentos utilizados foram seis cultivares de amendoim: IAC 505, IAC 503, IAC OL3, IAC OL4, EC-98 e Granoleico. Foram avaliados os componentes de produção (número de vagens por planta, número de grãos por vagem e peso de 100 grãos), produtividade, rendimento de grãos e índice de colheita. As cultivares IAC 505 e Granoleico tiveram o maior número de vagens por m-2. A cultivar EC-98 teve o maior peso de grãos e índice de colheita. A cultivar IAC OL3 teve o maior rendimento de grãos. As cultivares IAC 505 e IAC OL3 tiveram as maiores produtividades.

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In sandy soils with frequent drought events, the choice of cultivar and plant density is crucial to improve water use efficiency and avoid losses in cotton yield and fiber quality. This study aimed to evaluate cotton cultivars’ yield and fiber quality at different plant densities. The study was carried out during two growing seasons (2017/2018 and 2018/2019) on sandy soil in southeastern Brazil. The cultivar TMG 47B2RF showed 27 and 29% higher yields under low and medium plant density, respectively, when compared with the highest plant density. The higher yield was due to the higher number of bolls in relation to the cultivar DBB 509B2RF. The boll weight of cultivar DBB 509B2RF was 23 and 22% higher under low and medium plant density, respectively. Fiber length and strength were higher in TMG 47B2RF compared to DBB 509B2RF. The leaf nutrient content was higher in DBB 509B2RF, except for Ca and Mg. When there is a regular rainfall, the low plant density results in higher yields, but intermediate plant density is the best option in cropping seasons with severe drought. The high density of plants in sandy soil environments was never a better option for none of the cultivars.

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