Effects of slow-release urea one-time application on nitrogen reduction and efficiency improvement in maize cropping

【Objective】The effects of application rate reduction based on slow-release urea on maize yield and soil nutrient supply were discussed in order to provide the theoretical and practical basis for fertilization reduction and efficiency improvement in maize cultivation.【Method】Based on conventional nitrogen(N) fertilizer application(common urea at a N rate of 250 kg/ha), field plot experiments of common urea and slow-release urea application with a N reduction of 20% and 40% were conducted in this study. Soil N supply and crop N absorption dynamics, photosynthetic characteristics, activity of key enzymes for N assimilation and yield composition were measured for evaluating the potential of slow-release N fertilizer in N reduction and efficiency improvement under maize plantation.【Result】Compared with conventional Nfertilizer application, the 20% reduction of common urea and slow-release urea did not significantlydecrease the maize yield(P>0.05) but significantly increased the harvest index(P<0.05, the same below). Maize yield significantly reduced by 20.6%-22.5% at 40% N reduction relative to conventional N-fertilizer application. The shoot N uptake was significantly reduced in all N reduction treatments, and the root N uptake in 20% N reduction with slow-release urea was significantly higher than that in other treatments. Compared with the conventional N-fertilizer application, the apparent N use efficiency, stomatal conductance and photosynthetic N use efficiency of maize leaves were significantly increased by 20% N reduction. After 40% N reduction, the total N uptake, net photosynthetic rate and photosynthetic N use efficiency decreased significantly compared with the conventional N-fertilizer application. Glutamate dehydrogenase and glutamic oxaloacetic transaminase were sensitive to N reduction, and their activities were significantly reduced by 18.6%-61.0% and 13.8%-29.7%, respectively. Compared with the conventional N application, 40% N reduction significantly decreased soil nitrate-N content(except at seedling stage);the treatment of 20% N reduction significantly increased the ammonium-N content at each growth stage. The correlation analysis showed that the yield extremely positively correlated with biomass, harvest index, total N uptake, net photosynthetic rate, transpiration rate, stomatal conductance, photosynthetic N utilization rate and nitrate-N content at small bell stage, big bell stage, heading stage and maturity stage(P<0.01, the same below), and extremely negatively correlated with intercellular CO₂ concentration, and significantly negatively correlated with bald tip length, glutamate dehydrogenase, and ammonium-N content at big bell and heading stage. Nitrogen apparent use efficiency was significantly positively correlated with harvest index, extremely negatively correlated with glutamate dehydrogenase activity and significantly negatively correlated with glutamate-oxalacetic transaminase activity.【Conclusion】In maize plantation under the conditions of this study, both common urea and slow-release urea application with 20% N reduction can maintain maize yield, while the 40% N reduction would greatly reduce the yield. One-time application of slow-release urea has no significant advantages in yield and nutrient utilization compared with that of common urea under the same N reduction. The main factors influencing maize yield after N reduction are total nitrogen uptake, photosynthetic N use efficiency and soil nitrate-N content.