Abstract: Water and nutrient are the two main factors limiting Hevea brasiliensis growth and its latex yield. With 17 yearold Clone SCATC 7-33-97 H. brasiliensis as test material, the coupling effects of water and chemical N, P and K fertilizers on latex yield were studied by general orthogonal rotation design of quadratic regression with four factors and five levels under field condition, and a regressive mathematical model was set up based on the latex yield by quadratic regression analysis. The results showed that all test coupling levels of water and chemical fertilizers had significant effects on the latex yield. The yield-increasing effect of test factors was in the order of N application rate > irrigation amount > P application rate > K application rate, while the coupling effect of water and chemical fertilizers was in the sequence of water and N > N and P> water and P> water and K. There was a negative coupling effect of K application rate and soil moisture content. For latex yield, the optimum application rates of chemical fertilizers were 476.39 kg·hm^-2 of urea, 187.70 kg·hm^-2 of superphosphate and 225.77 kg·hm^-2 of potassium chloride, and the optimum irrigation amount was to have 82.78% soil relative water content.

Key words: phytoplankton, species composition, community structure, Bering Sea, Arctic.