Enhancing nitrogen and rainwater use efficiency through rainwater harvesting in semi-arid smallholder sorghum (Sorghum bicolor) farming systems

Abstract

Nitrogen and rainwater use efficiency in semi-arid smallholder farming systems is low due to low soil fertility and unreliable rainfall. The objective of this study was to evaluate the effect of rainwater harvesting and mineral nitrogen fertilizer on nitrogen and rainwater use efficiency under two sorghum (Sorghum bicolor) varieties. A split-split plot experiment, replicated three times, was conducted in Mt Zonwe smallholder farming area from 2016/17 to 2018/19. The results showed that water content under tied contour (TC) and infiltration pits (IP) had significantly higher water content compared to standard contour (SC) and moisture content significantly decreased with an increase in distance from RWH practices. TC and IP had higher agronomic efficiency than SC across all nitrogen applications, distance from RWH practice, and seasons. Sorghum variety Macia had higher nitrogen use efficiency indices than Sc Sila at nitrogen application of 50 and 70 kg N/ha while nitrogen application >100 kg N/ha had no difference in nitrogen use in both varieties. A decreasing trend in nitrogen productivity with an increase in nitrogen application was shown in both varieties. Mineral nitrogen fertilizer application increased rainwater productivity up to 100 kg N/ha beyond which there was no significant difference. Regardless of sorghum variety and season, TC and IP had higher rainwater use efficiency than SC at each distance from RWH practice. This study recommends the integrated use of TC and IP rainwater harvesting practices and mineral nitrogen fertilizer sustainably to improve N and rainwater productivity in semi-arid smallholder sorghum farming systems.