ABSTRACT
Conventional tillage (CT) has shaped agricultural landscapes for decades and has long-standing use in South Africa. However, recently, it has been criticised for being unsustainable, urging a re-evaluation of CT practices in the context of South Africa’s agricultural sustainability goals. This study investigates the effect of CA on soil profile distribution of P and N stocks in the Eastern Cape, South Africa. The trial is laid out in a randomised complete block design with strip-split-split plot treatment structure. The main plots, sub plots, sub-sub plots, and sub-sub-sub plots were allocated to 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-), and soil depths  0 – 20 cm, 20 – 40 cm, and 40 – 60 cm. Analysed soil samples were collected in the 2023/24 cropping cycle. The study results show that soil pH was significantly increased under CT with crop residue retention, particularly legume-based rotations like MFS and MWS. This could be because organic acids released during the decomposition of legume residues are often less acidic than those from cereal residues. Electrical conductivity was higher in NTR+ x MFM than CTR- x MWS at 0 – 20 cm owing to improved moisture retention. Phosphorus (P) and Total Nitrogen (TN) were concentrated at surface layers under NT, and this was attributed to reduced soil turnover and concentrated microbial activity in the upper layers. No-till improved ammonium (NH4+) retention while limiting nitrate (NO3-) leaching. Calcium and magnesium were more prominent at deeper soil layers (40 – 60 cm) owing to rainfall-induced leaching. On the other hand, potassium accumulated at surface layers, while sodium leached deeper, likely to its charge properties. Principal components showed TN, TP, pH, Na, and Mg as predictors for nutrient stocks, emphasising CA's positive effects on topsoil. While benefits extended to deeper layers, gradual improvements in soil health suggest CA's long-term sustainability. These findings reinforce CA's role in balancing soil productivity and ecological preservation.
Keywords: No-till, unsustainable, soil health, and sustainable development goals.