Long-term continuous tillage and fertilisation have a negative impact on soil fertility and carbon storage, adversly affecting sustainable development goals. The aim of this study was to examine the impact of nitrogen (N) application rate, N source, and tillage on soil fertility, total carbon (C), and total N under dryland cropping systems/ conditions. The treatments included no-till (NT), tilling every five years (CT5), and continuous tillage (CT1). Two N sources (urea and limestone ammonium nitrate (LAN)) were applied at 0, 60, 120, 180, and 240 kg N ha−1. The interaction between tillage, N application rate and source had no effect on micro- and macronutrients, total cations, exchangeable acidity, total C and N, and soil pH. No-till (NT) recorderd higher exchangeable bases, total cations, and zinc. Extractable phosphorus (P) was higher under NT compared to CT1, but not CT5. Increase in N rates decreased P, Ca, Mg, total cations, and soil pH and increased exchangeable acidity, acid saturation, and manganese. Copper was not affected by tillage and N application rates. Tillage and N source interaction affected Ca, and total cations. N source had no effect on all tested parameters, except for Ca and Mg. Whereases the interaction between tillage and N source only affected K. The NT had higher total C compared to CT1 and CT5 by 32.4 and 18.6%, respectively. NT had higher N compared to CT1 and CT5 by 34.6 and 45.5%, respectively. Total C increased over time in the NT and remained the same in CT1 and CT5. Whereas total N decreased in all tillage systems by more than 100%, except for the NT, where total N decreased by 64.2%. These findings support the literature that long-term NT has positive effects on soil fertility and carbon accumulation in drylands. However, total N showed a significant decrease over time with severe effects in CT1 and CT5.
Mkhungo et al. (2025) studied this question.