Qualidade do solo e produtividade do algodoeiro afetados por plantas de cobertura e sistemas de preparo

Abstract

The introduction of intensive production systems, such as cotton production, in sandy textured soils is increasing in Brazil; the type of management employed in these soils can negatively affect soil quality. However, the cultivation of cover crops can promote the increase of organic matter levels and improve the physical and biological conditions of these soils. The general objective of this study was to evaluate the production and fiber quality of cotton (Chapter 1) and the indicators of soil physical and biological quality (Chapter 2), carbon stock (C stock) and the chemical and physical fractions of organic C (Chapter 3) under the influence of cover crops millet and guinea grass in no-tillage (NT), minimum tillage (MT), fall tillage (FT) and Spring tillage (ST). The experiment was carried out during 2020/2021 and 2021/2022 seasons. The soil is classified as a Ferralsol with sandy texture. Cotton leaf carbohydrate content varied only in the 2020/2021 season, with higher values under ST, regardless of the cover crops. The ST+millet and MT+guinea grass resulted in a higher number of bolls and cotton yield in the 2021/2022 season. The MT+millet increased the micronaire, fiber length, and fiber strength, although all fiber quality parameters were suitable for commercialization. The NT, ST, and FT systems on millet improve the soil water storage capacity (cc/pt) showing compaction between 2,500 kPa and 3,200 kPa. The guinea grass under MT attenuated soil compaction by 23% and improved air storage capacity (par/pt), on the other hand, cc/pt increased under millet. The dehydrogenase activity was higher under NT with guinea grass. The microbial biomass carbon (Cmic) and soil respiration increased in NT+millet in 2020/2021 and decreased in the 2021/2022 season. In both seasons, millet under NT and MT increased the microbial biomass nitrogen (Nmic), while guinea grass favored Nmic increase under ST and FT. Glomalin content increased in NT+millet and MT+guinea grass in the 0.20-0.40 m layer. The C stock increased by 8% in NT, 5% under MT, and 5% in FT with millet compared to ST, respectively. The use of millet under NT increased stock organic carbon (SOC) in the 0.10-0.20 m layer compared to ST; however, in the 0.20-0.40 m layer, ST+millet increased SOC by 13% compared to the other tillage systems. In the 0.20-0.40 m layer, CAM increased under NT+guinea grass, but in the 0.40-0.60 m layer, millet was higher. The minerals-associated carbon (CAM) increased by 28% with millet at 0.10-0.20 m and by 17% with guinea grass compared to the FT in the same layer. The C lability increased by 32% with millet under MT in the 0.0-0.10 m, while C lability under guinea grass increased by 21% in the 0.10-0.20 m, respectively. When associated with guinea grass, MT increased the levels of fulvic acid (FA), humic acid (HA), HA:FA, humin, and humic substances (HS) at depth. Under NT+millet the AH and AH:AF was higher in the 0.0-0.10 m and 0.40-0.60 m. However, the NT+millet increased the humin and SH in the 0.40-0.60 m. The increase in the concentration of AH, AH:AF, and humin at 0.0-0.20 m was observed with millet in ST. Guinea grass under FT provided an increase in humin and SH in the 0.20-0.40 m between the cover crops. Our results suggest that millet under NT increases C stock at the surface of sandy soil and increased stable fraction of organic matter, improving soil physical and biological attributes. Even in a short planting window, millet with SF is a good option to increase cotton yield and surface C stock. Under better water availability, the MT with guinea grass improved the cotton yield, soil physical and biological attributes and C content.