Abstract
Background: Rain-fed maize production in semi-arid northern Nigeria is increasingly constrained by rainfall variability and inefficient soil water use. However, field-based quantification of soil water balance components and crop water productivity remains limited, restricting the development of effective climate adaptation and soil–water management strategies. This study quantified soil water balance components and crop water productivity of rain-fed maize (Sammaz-28) under semi-arid conditions.
Methods: A field experiment was conducted at the research farm of the Department of Agricultural Engineering, Ahmadu Bello University, Samaru-Zaria. Nine weighing lysimeters arranged in a completely randomized design with three treatments replicated three times were used to partition evapotranspiration (ET) into transpiration (T) and soil evaporation (E). Soil moisture dynamics were monitored using gypsum block sensors installed at depths of 5-70 cm, while surface runoff and deep percolation were quantified to establish the seasonal soil water balance.
Results: Daily ET ranged from 1.2 to 8.0 mm with a seasonal mean of 4.7 mm day⁻¹, and transpiration accounted for about 83% of total ET. Mulching reduced soil evaporation by up to 95%. Of the 511.5 mm seasonal rainfall, 21.9-26.0% was lost through deep percolation and 11.3-22.2% as surface runoff. Lysimeter-derived ET closely matched soil moisture depletion estimates (mean difference 1.26 mm week⁻¹; p > 0.05). Grain water productivity reached 2.23 kg m⁻³ under mulched lysimeter conditions compared with 1.46 and 1.29 kg m⁻³ in the open field and mulch-free lysimeter, respectively.
Conclusion: Surface mulching substantially reduced non-productive soil evaporation and improved grain water productivity. Integrating mulching with field-based water balance monitoring can enhance water use efficiency and climate resilience of rain-fed maize systems in semi-arid environments.

Key words: Keywords: Field study, Soil water balance components, Weighing-Lysimeter, Maize crop, Rain-fed condition