Least limiting water range as influenced by tillage and cover crop

Abstract

Brazil has been experiencing a trend of increased mechanization, although there are no studies addressing the relationship between tillage and cover crops, which affects soil physical attributes, cover crop dry biomass, roots dry biomass, yield, soil water content, and the influence on the least limiting water range (LLWR), defined as the range of volumetric soil water content in which limitations to plant growth occur. This study aimed to i) assess LLWR during two cycles in a sugarcane area using different cover crops and soil tillage systems; ii) correlate the LLWR with different soil physical attributes (soil bulk density, macroporosity and soil penetration resistance); and iii) evaluate the potential use of LLWR as an index of soil and crop quality. The study was conducted under field conditions in a sugarcane culture in the municipality of Ibitinga, São Paulo, Brazil. We used four cover crops (sunn hemp, millet, peanut and sorghum) and three soil tillage systems [no tillage (NT), minimum tillage (MT), and minimum tillage with deep subsoiling (MT/DS)] and compared them with a control treatment [conventional tillage with lack of plant cover (CT)] using an experimental design with split-plot scheme. The soil physical attributes were more affected during the cane cycle by the soil tillages and cover plants. Regarding soil water content, sunn hemp and sorghum obtained the highest soil water content over time with the use of MT/DS, also because the soil bulk density values using sunn hemp and sorghum MT/DS (1.64 and 1.59 kg dm−3, respectively) are 8% lower than the CT for the layer 0.15–0.30 m for the cane plant cycle. In what concerns LLWR, the treatments that maintained their soil water contents within the range for more than 3 months in a row were sunn hemp and millet MT/DS. LLWR was an important indicator, showing that the treatments that obtained LLWR equal to zero, even with high root growth and low penetration resistance, were not enough to express differences in productivity. This proved that the index aggregates all the information and produces satisfying results.