Suitable amount of N topdressing based on leaf age index of maize using mulched drip irrigation technology in Western Songnen Plain

【Objectives】 The mulched drip irrigation technology has been extended in the production of maize in Western Songnen Plain. Studying the suitable N fertilizer application amount and leaf age of maize under this technology system will provide a theoretical basis for efficient water and fertilizer efficiency and high-yield maize production.【Methods】 At the basal fertilizer levels of N 60 kg/hm2, P2O5 90 kg/hm2 and K2O 120 kg/hm2, four topdressing levels of N 0, 40, 90 and 140 kg/hm2 were top dressed at the leaf age index of 30%, 45%, 60% and 75%, respectively. Drip irrigation equipment was used for the fertilization. The photosynthetic efficiencies, the dry matter accumulation and the grain yields of corn in different growth stages were measured, and the N efficiencies were calculated. 【Results】Along with the advancement of maize growth process, the grain yield, leaf area index, chlorophyll content, dry matter accumulation and nitrogen accumulation of maize, nitrogen utilization efficiency, nitrogen agronomic efficiency and nitrogen harvest index are increased with the raising of nitrogen application rate in a certain range (0-150 kg/hm2) of nitrogen application. When the nitrogen usage exceeds a certain amount (200 kg/hm2), there were no more increases or even fallen in the above items tested. In the treatment of topdressing at the leaf age index of 45% and the nitrogen application rate of 90 kg/hm2, the grain yield reaches to 11957.89 kg/hm2, the leaf area index and chlorophyll content are 6.92 and 2.69 mg/g, the dry matter accumulation amount, post-anthesis assimilate inputs to grains, and contribution of post-anthesis assimilates to grains are 423.76 g/plant, 14451.50 kg/hm2, and 85.86% respectively. And the nitrogen utilization efficiency and nitrogen agronomic efficiency are 69.10% and 38.38%. All the mentioned items are significantly higher than those in the other treatments(P0.05).【Conclusions】 In Western Songnen Plain under the mulched-drip irrigation condition, the suitable N topdressing amount is 90 kg/hm2, and preparatory leaf age for the practice is at leaf age index of 45%.