Defining tillage need for edible bean production under no-tillage: Classical and time series analyses

Mechanical amelioration techniques may be used in long-term no-till compacted soils to improve soil structure and increase crop yield. The objectives of this study were to investigate the effect of ploughing and chiseling on changes in soil physical properties, quantify the number of days that the soil moisture is outside the critical limits of the least limiting water range, compare crop performance, and define the best tillage method using classical and applied statistical analysis. Treatments consisted of continuous no-tillage for 5 years (NT), disc plough (Plo) and chisel plough (Chi) both on soil previously under no-tillage for 5 years. High degree-of-compactness and low least limiting water range on the medium-term no-tillage Acrisol justified the need for evaluating inverting and non-inverting tillage. Soil penetration resistance, dry bulk density, soil temperature, and volumetric moisture content was measured at different times and soil layers during bean growth and development, and correlated with black bean roots distribution and yield. Soil moisture content and temperature data were subjected to time-series analysis. Low penetration resistance was observed in the 0.03 – 0.05 m soil layer, which was greater in NT than in Plo or Chi soil, but always below 1.5 MPa. During the cropping season, spatial variations in penetration resistance was lesser in the deep soil layers compared to the surface layers, following the trend on lower oscillations in soil moisture. Soil bulk density at 0.075 m depth decreased due to soil disruption: 1.72, 1.65 and 1.52 Mg m⁻³ for NT, Chi and Plo, respectively, and increased with soil depth. The number of days the soil was in good moisture conditions had the order Plo ≈ Chi > NT. Although no-till soil is near the critical/restrictive condition to crops and soil tillage improves soil quality, tilling does not guarantee increased crop yield. The degree-of-compactness and the least limiting water range do not capture soil physical quality for bean growth and yield. Soil tillage influenced the autocorrelation and cross correlation of soil water content in all soil layers. The estimation of soil water content using state-time analysis was affected by soil management, with the best performance from Chi soil. Significant temporal relations were observed between soil water content and other soil-atmospheric variables, with rainfall being the highest controlling factor. The time series analysis can be combined with classical and spatial statistics, for assessing soil quality under different management based on local environmental properties and climatic conditions.