[Effects of water conditions and controlled release urea on yield and leaf senescence physiological characteristics...

In an soil column experiment with Zhengdan 958 (a summer maize cultivar planted widely in China), treatments of three water levels,severe water stress W₁ which the soil moisture kept (35±5)% of the field capacity, mild water stress W₂ which was (55±5)%,normal water W₃ which was (75±5)%, and four levels of controlled release urea fertilizer (N₀, N₁ was 150 kg N·hm^-2,N₂ was 225 kg N·hm^-2 and N₃ was 300 kg N·hm^-2) were included to study the interactive effects of water and controlled release urea on yield and leaf senescence characteristics of summer maize. The results showed that the coupling of water and controlled release urea had significant effects on increasing yield, delaying the senescence and keeping the high efficiency of the functional leaves. Under the same nitrogen condition, yield, LAI, chlorophyll content and the activities of SOD, POD, CAT and soluble protein content in summer maize ear leaf were significantly increased with more water supplying, and the content of MDA decreased significantly. Under the condition of the same moisture, these indicators were also significantly increased with the increasing nitrogen application and MDA content was reduced significantly. However, these indicators (except MDA) of W₃N₃, W₃N₂ and W₂N₃ treatments were maintained at a higher level and the MDA content was lo-wer compared with other treatments despite the fact that there were no significant difference among these three treatments, which indicated that the interactive effects of water and controlled release urea had an important role in maintaining the function of ear leaf, delaying the leaf senescence, and was beneficial to the photosynthates production and obtaining higher yield of summer maize. Integrating the yield, LAI, chlorophyll content, various protective enzymes activity, MDA and soluble protein content, controlled release urea application rate of 225 kg N·hm^-2 was the best treatment as the soil moisture content was (75±5)% of field capacity. Continuous increase in the nitrogen application could not enhance the activities of protective enzymes, oppositely, it could cause the decline of protective enzymes activities and the increase of MDA content rapidly and speed up plants translation to senescence, which was not conductive to the efficient use of nitrogen. We suggested that coupling controlled release urea application rate of 300 kg N·hm^-2 with soil moisture content of (55±5)% of field capacity was optimum.