Integrating bio char and deficit irrigation to improve sorghum productivity, soil moisture retention, and water-use efficiency under semi-arid conditions

Abstract:

Water scarcity and progressive soil fertility decline are the most critical constraints confronting dryland cereal production across sub-Saharan Africa. Sorghum (Sorghum bicolor L. Moench) occupies a pivotal role in the food security of semi-arid communities, yet its attainable yield is persistently undermined by erratic rainfall distribution and structurally poor soils with low water-holding capacity. This study investigated the independent and combined effects of biochar amendment rates (B₀: 0, B₁: 5, B₂: 10, B₃: 20 t ha⁻¹) and deficit irrigation levels (I₁: 100%, I₂: 75%, I₃: 50% of crop evapotranspiration, ETc) on sorghum growth, grain yield, soil moisture retention, and water-use efficiency (WUE) under semi-arid conditions in Tigray, Ethiopia. A 4×3 factorial randomized complete block design (RCBD) with three replications was implemented over two consecutive cropping seasons (2022–2023). Results demonstrated that the B₃I₂ interaction (20 t ha⁻¹ biochar + 75% ETc) significantly outperformed all other treatment combinations, producing a mean grain yield of 3.62 t ha⁻¹ and WUE of 1.84 kg m⁻³, corresponding to 49.2% and 58.6% improvements over the non-amended full irrigation control (B₀I₁), respectively. Volumetric soil moisture content at 0–20 cm depth in biochar-amended plots declined by only 12.4% under 75% ETc, compared with a 31.7% decline in unamended plots under equivalent irrigation deficit. Analysis of variance confirmed highly significant (0.01) main and interaction effects for all measured parameters. These findings demonstrate that high-rate biochar effectively buffers soil moisture depletion and sustains sorghum productivity under constrained water inputs, establishing biochar-assisted deficit irrigation as a viable climate-smart strategy for smallholder dryland farming systems in semi-arid Ethiopia and analogous agro-ecological zones.