Aggregate stability and soil surface sealing in irrigated soils under no-tillage versus conventional tillage

The effect of no-tillage (NT) (zero tillage) versus conventional tillage (CT) has been evaluated in rainfed conditions but has seldom been studied under irrigation, where soil sealing favours soil degradation. To contribute to this knowledge, this research analyses soil aggregate stability under disaggregation forces produced under irrigation (causing slaking and mechanical breakdown) and the susceptibility to soil sealing in soils cropped with irrigated maize. Soils were sampled from 0 to 2 and from 0 to 5 cm before maize planting. Soil aggregate stability against both disaggregation processes was expressed by the mean weight diameter (MWD). Soil organic carbon (SOC) was evaluated in aggregates of different size fractions that remained after the disaggregation processes. Soil sealing susceptibility was characterised by the saturated hydraulic conductivity. The results confirmed the high disruption effect of slaking and mechanical breakdown processes. The MWD under those processes was up to 50% smaller and the susceptibility to seal was about three times higher in the soils under CT than under NT. The results of the top 0-2 cm layer showed an aggregate stability against mechanical breakdown 30% smaller than the 0-5 cm layer, which could be due to the soil surface sealing caused by drop impact. Greater MWDs were related to higher SOC values in the aggregates, which were about 20% higher in the soils under NT than under CT. Thus, NT represents an effective management in irrigated soils, reducing soil sealing and helping to maintain greater aggregate stability in soil surface against the disaggregation forces caused by drop impact and wetting processes.