Medium-term effects of tillage, crop rotation and crop residue management practices on selected soil physical properties in the sub-humid region of Eastern Cape, South Africa

The conservation agricultural effects on soil physical properties are not immediately visible and are variable but might be observed in medium to long-term studies. The objective of this study was to assess the medium-term (ten year) effect of conservation agricultural practices on selected soil physical properties in a sub-humid region of Eastern Cape, South Africa. The assessment was performed on a conservation agriculture (CA) field trial established in 2012, laid out in a randomized complete block design (RCBD) with split split-plot treatment structure consisting of 16 treatment combinations replicated into 3 blocks. The main plots, sub plots and sub sub plots were allocated to tillage (no-tillage (NT) and conventional tillage (CT)), crop rotations (maize-fallow-maize (MFM); maize-soybean-maize (MFS); maize-wheat-maize (MWM); maize-wheat-soybean (MWS)), and crop residue management practices (residue retention (R+) and residue removal (R-)), respectively. Soil samples were collected from 0 – 10, 10 – 20 and 20 – 30 cm depths in the 2023/24 cropping season. The results showed that tillage practices had a significantly greater impact on bulk density (BD), porosity (ϕ) and aggregate stability (AGS)/ stability index (SI) compared to crop rotations and residue management. Soybean rotation treatments: MFS and MWS had 3.42 % and 2.08 % lower BD values compared with MFM and MWM, respectively. This is likely due to the quick decomposition of soybean residues, indicating potential improvement in soil health and soil quality with legume inclusion in rotations. Additionally, R+ plots had 24.24 % higher gravimetric water content and 25.04 % higher volumetric water content than R- plots, due to the substantial amount of SOM returned by residue decomposition. There were no significant differences observed in Ks, which could be attributed to the nature of the particle size distribution, as water moves more easily on sandy soils. These medium-term results present continual benefits from proper implementation of CA in sustainable farming and resource conservation.