Optimizing Planting Densities, Irrigation and Nitrogen Topdressing to Improve Bioavailable Soil Water and Yield and Quality of Winter Wheat

Abstract

【Objective】 Water and fertilizer use efficiency of crops depends on many factors, and the objective of this paper is to investigate experimentally how to achieve this through optimizing planting density, irrigation and nitrogen topdressing. 【Method】 The experiment was conducted in lysimeters with winter wheat used as the model plant. It compared two planting densities: 5×106 plant/hm2 (D1) and 3×106 plant/hm2 (D2). For each planting density, there were three irrigation treatments: irrigating at the turning-green stage and the grain-filling stage (W1), irrigating at the turning-green stage, jointing stage and grain-filling stage (W2), irrigating at the turning-green stage, jointing stage, heading stage and grain-filling stage (W3), and two nitrogen topdressing treatments: topdressing all nitrogen at the turning-green stage, topdressing a half at the turning-green stage and the other half at the jointing stage. In each treatment, we measured the changes in soil water contents. 【Result】 Irrigating scheduling W2 made soil water in 0~100 cm more suitable for the crop to grow and increased its water use efficiency. Increasing irrigation frequency enhanced photosynthetic and transpiration rates, but it reduced leaf water use efficiency and the content of amino acid and protein in the grain. Increasing planting density or nitrogen topdressing frequency can improve photosynthetic rate even when the total amount of nitrogen application was the same. Increasing planting density increased spike numbers, but reduced grain numbers per spike and kernel weight, all at significant level (p<0.001). Irrigation scheduling affected grain numbers per spike, kernel weight, crop yield, and irrigation water use efficiency (IWUE) at significant level (p<0.05); increasing irrigation frequency at different growing stages increased the kernel weight but reduced IWUE. Irrigation scheduling W2 gave the highest grain numbers per spike and yield, followed by W3, with W1 being the least. When the amount of nitrogen used in the topdressing was the same, increasing topdressing frequency increased the kernel weight and yield significantly, but reduced the content of amino acid and protein in the grain. Planting density did not show significant effects on amino acids and protein in the grains. Regression analysis revealed that the content of amino acid and protein in the grains decreased linearly as the crop yield increased. 【Conclusion】 The optimal agronomic practices for winter wheat in our studied regions were: Planting density 3×106 plant/hm2; three irrigations, each with 75 mm of water, at the turning-green stage, jointing stage and grain filling stage respectively; base fertilization N, P2O5 and K2O, each at the rate of 90 kg/hm2; topdressing nitrogen at the turning green stage and jointing stage, each with 60 kg/hm2.

Keywords

• planting density
• irrigation scheduling
• topdressing nitrogen
• winter wheat
• yield
• grain quality