The influence of sowing furrow opening and wetting and drying cycles on soil physical quality under no-tillage in Southern Brazil

Soil disturbance from seed drilling and fertilizer application promotes structural changes that impact the physical quality of soil under no-till (NT). This study tests the hypothesis that spatial and temporal changes to crop rows and interrows along the occurrence of wetting and drying cycles promote changes in soil physical quality under NT. Undisturbed soil samples were taken from 0.0−0.10 m and 0.10−0.20 m depths in a Rhodic Ferralsol under long-term NT on five successive dates, from within the row (R), interrow (IR) and an intermediate distance between the row and interrow (IP). In addition to the spatial and temporal variation of the sampling position, the occurrence of wetting and drying cycles (WDC) was considered. The undisturbed samples were used to determine soil bulk density (BD), soil water retention and penetration resistance curves and the least limiting water range (LLWR). At the 0.0−0.10 m depth, there were systematically lower BD at the R position than at the IR and IP, whereas for the 0.10−0.20 m depth there were no differences among the sampling positions. The LLWR were significantly higher for R compared with IR and IP, suggesting more favourable soil physical conditions for plants at the R position. For the different sampling dates, it was found that there were significant variations in the physical quality of the soil at 0.0−0.10 m while slight variations regardless of the sampling position were verified at the 0.10−0.20 m depth. The changes in soil physical quality within crop rows as well as due to the WDC were only verified at 0.0−0.10 m depth. The WDC impacted the soil physical quality at the IR and IP positions, while soil disturbance during the drilling improved soil physical quality at the R position. The absence of soil disturbance and the reduced magnitude of WDC did not alleviate the soil compaction at the 0.10−0.20 m depth. The temporal variation of rows and interrows induced by crop rotation in areas under NT seems to be a mechanism that alleviates surface soil compaction. In fields managed under NT, the identification of sampling positions, especially of R or IR areas, is fundamental for the proper interpretation of soil physical quality indexes given that R and IR dynamics over time can modify the soil physical properties.