Effect of deficit irrigation on water productivity and yield attributes of maize

Abstract:

Water productivity, not simply water availability, is the metric increasingly setting the ceiling on irrigated maize expansion across water-scarce farming regions. Field research over two consecutive dry seasons at Lusaka tested four irrigation levels, 100%, 80%, 60%, and 40% of crop evapotranspiration (ETc), to determine their combined effect on grain yield, yield components, and water productivity of maize. Full irrigation (100% ETc) produced the highest grain yield at 7860 kg per hectare, but water productivity peaked instead at 80% ETc, reaching 1.42 kg per cubic meter of water applied against 1.21 kg per cubic meter under full irrigation. Yield fell by 24% under 60% ETc and by 45% under 40% ETc relative to full irrigation, with the steepest yield losses concentrated in kernel number per cob rather than kernel weight, pointing to the silking and pollination window as the growth stage most sensitive to water deficit. Harvest index declined progressively as irrigation level decreased, falling from 42.6% under full irrigation to 31.8% under the most severe deficit treatment. These results identify 80% ETc as a water productivity optimum that sacrifices only a modest yield margin for a meaningful gain in water use efficiency, a trade-off directly relevant for irrigation scheme managers allocating water across competing demands during dry seasons when full irrigation supply cannot be guaranteed for every scheme member.