Thiourea Supplementation Improves Drought Stress Response of Ridge-Sown and Mulch-Applied Rainfed Maize (Zea mays L.) via Improved Leaf Source to Grain Sink Dynamics

In regions of South Asia where rainfed maize is grown, effective crop management during drought is essential for maximising yield. A variety of water-conserving planting practices are used, and more recently, techniques such as foliar supplementation to maintain nutrients during drought have also shown promise. However, specific combinations of these approaches are often untested for optimality. Here, we explore the effects of two maize planting practices (ridge sowing and mulching) to conserve water, in combination with foliar thiourea. Drought stress response of crop was assessed at two experimental sites (L-I and L-II), through split-plot design (main plots: flat sowing + mulch, flat sowing, ridge sowing + mulch [RS + M] and ridge sowing; sub-plots: unsprayed, water spray, 500 ppm thiourea and 1000 ppm thiourea). Plant performance was assessed via dry matter accumulation, grain growth rate, stomatal parameters, grain yield, stover yield and nitrogen uptake. Rainfall breaks induced three dry spells during the pre-anthesis and grain-filling period. RS + M showed maximum drought tolerance by enhancing rainwater and nutrient use (N uptake [88.1 and 115.1 kg ha⁻¹]) and recorded significantly higher periodic dry matter accumulation (149.2 and 156.8 g) along with higher 1000-grain weight (181.0 and 196.6 g), grain-filling duration (36.3 and 34.9 days) and leaf health parameters over the flat-sown treatments. Furthermore, foliar supplementation of thiourea at 1000 ppm caused improved leaf health, likely through activation of a source to sink response (transfer of energy and materials from leaves to other plant organs) that alleviated moisture stress. Ultimately, the combination of RS + M and 1000 ppm thiourea led to the highest grain yields (32.1 and 39.5 qha⁻¹).