Abstract: A experiment using Zhengdan 958 (a summer maize cultivar planted widely in China), with treatments of three water levels (normal water W3, mild water stress W2, severe water stress W1) and four amounts of controlled release urea nitrogen (N) (N3 was 315 kg ha^-1, N2 was 210 kg ha^-1, N1 was 105 kg ha^-1 and N0 was no nitrogen) was carried out under the waterproof shed and potting conditions. The results showed there was significant influence of coupling water with controlled release urea on yield and photosynthetic characteristics in summer maize. Under the condition of same soil moisture, the yield showed a increasing trend with the amounts of N application increased. The yield increased by 13.17%-20.96% under severe water stress (W1), by 13.93%-32.48% under mild water stress (W2), and by 14.37%-21.83% under the condition of normal water (W3). Under the same amounts of N application, the yield was also improved with the increase of the soil moisture. The yields of W2N3, W3N2, and W3N3 were the highest among these treatments. The coupling effects of water and controlled release urea were significant on the photosynthetic rate in ear leaf. The photosynthetic rates of N3, N2, and N1 had no significant differences in W1, and were higher than these of N0 significantly. The photosynthetic rate of W2 and W3 treatments increased with the increase of N fertilizer application, the average photosynthetic rate in W3 was higher than that of W2 and W1, that of W2N3 was slightly lower than that of W3N3 and W3N2 at early flowering, and no significant difference in the late stage. The coupling effects of water and controlled release urea nitrogen could effectively improve the efficiency of light energy utilization and slow down the decline rates of the actual photochemical efficiency of PSII, coefficient of photochemical quenching (q_P) of leaf and PSII reaction center of light conversion. High photosynthetic rate, actual and maximal photochemical efficiency of ear leaf after flowering in summer maize ensured the nutrients needs of grain filling, thus increased the yield. Higher yield was obtained due to the significant increase of kernels per ear and thousand seed weight among yield components. Under this experimental condition, controlled release urea N application rate of 210 kg ha^-1 was the best treatment as the soil moisture content was 75%±5% of field capacity. We suggested that coupling controlled release urea N application rate of 315 kg ha^-1 with soil moisture content of 55%±5% of field capacity is optimum.

Key words: Summer maize, Controlled release urea, Water and nitrogen coupling, Yield, Photosynthetic characteristics