Sprinkler irrigation increases grain yield of sunflower without enhancing the risk of root lodging in a dry semi-humid region

Abstract

Sunflower (Helianthus annuus L.) is an important edible oilseed crop that is frequently exposed to drought stress due to lack and unpredictability of precipitation. Sprinkler irrigation (SI) is a promising approach for improving yield under limited availability of water, but is often associated with increased risk of root lodging. The irrigation water can soften the upper soil layer and increase the torque of the aboveground portion of the crop. This study aims to evaluate the effect of SI and nitrogen (N) application rate on grain yield, water use efficiency (WUE), and root lodging resistance of sunflower. The risk of root lodging was evaluated by a “safety factor” (SF) indicator. The results showed that soil water content (%) was 13.4 and 19.1% higher under SI in comparison with rainfed (RF) conditions in 2018 and 2019 respectively, when averaged across the whole measured period. Sprinkler irrigation exhibited 12% higher mean grain yield than RF conditions across both years (P < 0.05), although WUE was not influenced. The yield advantage under SI was supported by strong relationships of grain yield with harvest index, aboveground biomass and yield components. A positive yield response to increasing N rate from 0 to 180 kg N ha–1 was evidenced, beyond which no response was observed. Root lodging resistance in terms of SF increased with higher N application rate due to decrease in anchorage strength. Root lodging resistance between SI and RF treatments was not significantly different due to the trade-off between anchorage strength and self-weight moment, although irrigation water under SI weakened the soil shear strength and reduced the anchorage strength estimated by a theoretical model. Taken together, SI in combination with an N rate of 180 kg ha–1 could be recommended to mitigate drought stress and improve grain yield and root lodging resistance of sunflower.