Water productivity and seed cotton yield in response to deficit irrigation: A global meta-analysis

The scarcity of water resources has posed serious threats to the sustainable development of agriculture and promoted the need for water-saving technologies. Deficit irrigation has been widely used as a water-saving practice globally. Although it does facilitate the improvement in crop water productivity (WP), its influence on crop yield varies considerably. Therefore, a global meta-analysis was conducted to systematically and quantitatively analyze the responses of both WP and seed cotton yield to deficit irrigation, and explore the optimal conditions for the better application of deficit irrigation in practice. It was found that, although deficit irrigation averagely increased WP by 5.3% compared with full irrigation, it caused a significant decline in seed cotton yield by 20.2% on average. Overall, deficit irrigation performed best at the seedling+blooming stage of cotton under 80–100% full irrigation, in regions with seasonal precipitation ≥ 120 mm and average annual temperature ≥ 10 ℃. Cotton planted in medium textured soils with bulk density ≥ 1.35 g cm−3 obtained highest seed cotton yield and WP. Seed cotton yield and WP were increased by ridge planting with film mulching. Additionally, drip irrigation was most beneficial for seed cotton yield than sprinkler and furrow irrigations. Deficit irrigation throughout the whole growing season of cotton was the most undesirable measure. Seed cotton yield and WP were significantly affected by fertilization rate, and the appropriate nitrogen, phosphorus and potassium application rates were 300–400 kg N ha−1, 79–105 kg P ha−1 and 100–133 kg K ha−1, respectively. In conclusion, higher WP was obtained with acceptable reduction in seed cotton yield under deficit irrigation. However, to optimize deficit irrigation in practice, irrigation method and amount, deficit stage, climate condition, soil property, mulching mode and fertilization rate must be further considered.