Produtividade da soja e distribuição de raízes em solos com variabilidade de atributos físicos e químicos em safra com estiagem

Abstract

The existence of soil layers with physical and/or chemical limitations at depth in the soil are common in Rio Grande do Sul’s crops. These conditions hinder the root growth of soybean crops in deeper layers. The distribution of roots within the soil profile has a direct influence on soybean yield and is modulated by rainfall patterns throughout the crop cycle. Root concentration in surface layers has minimal impact on yield during well-distributed rainfall years, but can cause significant losses during irregular rainfall years, especially in reproductive stages with water scarcity. However, the relationship between soybean’s drought tolerance and root distribution profile is not yet well understood. In this study, different soybean root distribution profiles were evaluated in two studies. In the first study (Article I), the effectiveness of occasional soil mobilization under no-tillage system and deep chemical correction was tested as a strategy to increase root depth and mitigate the impact of water deficit on soybean yield. Three treatments were evaluated: surface application of limestone, P, and K = QAsup, chiseling followed by QAsup = CH_QAsup, chiseling followed by QAsup and plowing = CH_QAsup_PLO. Occasional soil mobilization resulted in a higher concentration of roots in the mobilized layer. In this layer, there was a reduction in water availability due to the lower soil retention capacity resulting from mobilization. This limited soybean productivity due to lower supply in the layer with a higher concentration of roots. The use of chemical correctives improved chemical conditions in depth but did not prevail in root deepening. In the second study (Article II), a diagnosis of soybean root distribution was conducted in different soils in the state of Rio Grande do Sul. Soil and root samples were collected at various depths from 10 locations in the state. Additionally, precipitation data were measured in the Barra do Ribeiro, Bossoroca, Cacequi, Marau, and Tuparendi fields and obtained from meteorological stations closest to the fields in Cachoeira do Sul, Cruz Alta, Ibirubá, Pinhal Grande and São Pedro do Sul due to the lack of measurements in the respective cultivated areas. The results of this study indicate that almost all fields have limitations, either of a physical or chemical nature, and in some cases, both, which restrict root deepening. In locations with well-distributed rainfall, plants managed to meet their water demand even with roots concentrated in the layers close to the soil surface. However, this configuration severely limited soybean yield during periods of low rainfall. It is evident, therefore, that improving chemical conditions in the deep soil is necessary in most state soils and can enhance root deepening as long as physical conditions are not limiting. In terms of physical management, mechanical soil compaction can be detrimental to root deepening and should be avoided.