Abstract:The reasonable ratio of water and fertilizer for maize planting has been an important subject in agricultural research. However, previous studies only pay more attention to the one of the factors of yield, water use efficiency and photosynthetic rate, etc. to make the scheme of water and fertilizer coupling. The purpose was to reveal the coupling effects of fertilizer and water on photosynthetic rate, yield and WUE. A scheme of water and fertilizer combination was made based on the multi-objective genetic algorithm (MOGA), aiming to achieve an overall optimization of the above three factors. The D-416 saturation optimum design with 16 treatments and three replicates was used in the experiment. There were four levels of irrigation amount (400.0m3/hm2, 473.7m3/hm2， 604.1m3/hm2 and 700.0m3/hm2), five levels of N supply (180.0kg/hm2, 198.3kg/hm2, 225.0kg/hm2, 251.7kg/hm2 and 270.0kg/hm2), and five levels for both of P2O5 and K2O (60.0kg/hm2, 72.2kg/hm2, 90.0kg/hm2, 107.8kg/hm2 and 120.0kg/hm2). The design of each block was 10.4m×10m with 702 plants and 23cm in spacing. Maize variety of Longdan 9 was selected to seed on April 25, 2016. P2O5 and K2O were supplied as base fertilizer before seeding. Half of N was used as base fertilizer and the remaining half was applied at elongation stage. Each treatment was irrigated respectively at elongation stage and tasseling stage with the same amount of water. The photosynthetic rate of the fourth leaf from the top to the bottom of maize was measured by the LI-6400 (LI-COR Biosciences Company, USA) during 09:00—11:00 on August 9, 2016. The yields for each block were recorded on September 21, 2016. The regression model of N, P2O5, K2O and irrigation water amount on maize photosynthesis rate was established by four-factor quadric regression analysis, and the coefficient of determination was 0.99. Sorting from large to small, the effect of various factors on the photosynthesis rate of maize was irrigation water amount, N, K2O and P2O5. The photosynthetic rate appeared the trend of increasing first and then declining with the increase of each factor. Coupling effects between irrigation water amount and N, P2O5 and K2O, irrigation water amount and K2O were significant while the coupling effects between the rest factors were not significant. The medium irrigation and medium fertilizer were favorable for maize photosynthesis. Increasing yield was beneficial to improve WUE. A multi-objective optimization model of photosynthetic rate, yield and WUE of maize was established. The genetic algorithm was used to optimize this model. The most suitable combination of irrigation water amount and fertilizer was as follows: irrigation amount was 700m3/hm2, and the fertilizer was 270kg/hm2 of N, 60.26kg/hm2 of P2O5, 60.02kg/hm2 of K2O and the corresponding optimum maize photosynthetic rate, yield and WUE were 13.54μmol/(m2·s), 24520.10kg/hm2 and 5.14kg/m3, respectively. The results had a guiding role in maize production.
