Balancing crop water requirements through supplemental irrigation under rainfed agriculture in a semi-arid environment.

Rainfed farming is a dominant agricultural system in Tigray, Ethiopia. However, rainfall is characterized by short duration, intense and erratic subjected to late-onset and early cessation, suggesting a pressing need for Supplemental Irrigation (SI) to fill the crop water demand. Understanding the effects of SI during rainfall late-onset, early cessation, or both, along with their underlying causes, is a critical knowledge gap globally. Although wheat is one of the principal food crops in Tigray, it is subjected to moisture stress during critical growth stages, limiting its potential productivity. Studies specifically related to impacts due to the late-onset of rainfall on wheat are non-existent. Here, we investigated the agrometeorological characteristics of rainfall variability, onset, cessation, and length of the growing season to evaluate the use of SI for balancing the moisture stress in rainfed farming. Meanwhile, using an on-farm experiment, we also evaluated double-season (2017 and 2018) SI application during late-onset (Pre), early cessation (Post), and its combined effects (Pre + Post) on yield and water productivity (WP) of wheat. Yield and WP were significantly (P < 0.05) affected by SI application with higher grain yield (3298 kg/ha) and WP (0.538 kg/m) obtained from applying Pre + Post. Applying Pre + Post has increased grain yield, biomass, and WP of wheat by 45.6, 27.7, and 21.5% over Rain-fed farming, respectively. Thus, balancing crop water requirements using SI during inadequate rainfall distribution is key for improving WP and wheat production in semi-arid environments. Particularly, the application of SI both during the late-onset and early cessation of rainfall is suggested for greater wheat productivity in semi-arid regions.