Least limiting water range (LLWR) of Oxisol under native cerrado and minimum soybean tillage

Abstract

Understanding how production systems influence soil structure is important, because excessive compaction represents a major obstacle to water availability to plants. In this context, this study aimed to determine the impact of minimum tillage system in Oxisol under soybean, for eight years in succession, on the physical characteristics of the soil in 0-10, 10-20 and 20-30 cm layers and the correlation of these attributes with the least limiting water range (LLWR). An area of native cerrado was used as reference of soil physical quality.   It was possible to verify that the hypothesis that soil physical properties such as density (Ds) and soil organic matter, wet stable macroaggregates (4-2 mm), determined separately in an attempt to predict possible soil water restrictions for the development of plants imposed by structural degradation is valid, since they were correlated with the LLWR. Compared to native cerrado, soil structural degradation under minimum soybean tillage was more pronounced in the 0-10 cm layer due to higher Ds, lower stability of macroaggregates, organic matter and soil flocculation level, where more than 60% of Ds samples were above the Dscritical (LLWR = 0), resulting in a significantly lower LLWR. Regarding the parameters that define the LLWR, it was possible to observe that, under minimum tillage, there was greater proportion of samples, where θPA and θRP-limit (2.0 or 2.5 MPa) replaced θCC and θPMP, respectively. However, θRP-limit was the main factor for LLWR reduction.