Differences in maize photosynthetic characteristics and nitrogen regulation effects in maize/soybean and maize/sweet potato relay strip intercropping

Maize/soybean and maize/sweet potato relay strip intercropping systems are the two main intercropping systems in Southwest China. In two main maize production areas in Sichuan Province, differences in photosynthetic characteristics of maize under maize/soybean and maize/sweet potato relay strip intercropping systems were investigated based on long-term experiment (2008-2010). Also the data for 2011 was used to investigated the effects of nitrogen application rates on maize photosynthetic characteristics with the split-plot design experiment of different nitrogen application rates 0 kg(N) hm^-2 (N0), 90 kg(N) hm^-2 (N90), 180 kg(N) hm^-2 (N180), 270 kg(N) hm^-2 (N270) and 360 (N360) kg(N) hm^-2 in maize/soybean and maize/sweet potato relay strip intercropping systems. Differences in photosynthetic characteristics in maize were determined based on analysis of leaf area index, relative content of chlorophyll, nitrogen content in ear leaf, photosynthetic rate and chlorophyll fluorescence parameters. Results showed that different planting patterns and nitrogen managements had fine adjustment effects on photosynthetic characteristics of maize. Compared with the traditional relay strip intercropping pattern ― maize/sweep potato relay intercropping system, maize/soybean relay intercropping system significantly slowed down the decreasing rates of leaf area per plant and the relative content of chlorophyll from filling stage to maturity stage, increased the activity of PSⅡ in ear-leaf and photochemical efficiency. Consequently, under maize/soybean relay intercropping, maize photosynthetic rate increased, and biomass per plant at maturity stage was higher by 10.49 g over that under maize/sweet potato relay intercropping. After strip crop rotation, the differences in all the indexes of photosynthetic characteristics since tasseling stage between the two cropping patterns were significant. Under maize/soybean relay strip intercropping, leaf area per plant, net photosynthetic rate, and ear-leaf Fv/Fm and ФPSⅡ were higher after flowering stage respectively by 941 cm², 4.81 ?mol·m^-2·s^-1, 0.017 and 0.020 than those under maize/sweet potato system. From filling to maturity stages, the decreasing rates of all the indexes of maize/soybean relay intercropping were obviously lower than those of maize/sweet potato relay intercropping. Maize biomass per plant at maturity stage of maize/soybean relay intercropping was higher by 26.83 g than that of maize/sweet potato relay intercropping. Maize leaf area per plant and chlorophyll fluorescence parameters increased under treatment N180 for maize/soybean relay intercropping system, and under treatment N270 for maize/sweet potato relay intercropping system, with both treatments having increased photosynthetic rate and biomass accumulation. Excessive application of nitrogen (270-360 kg·hm^-2) deceased chlorophyll content, leaf Fv/Fm and ФPSⅡ and photosynthetic rate in both intercropping systems.