No abstract

To relieve the situation of the agricultural nonpoint pollution (NPS) in south and east China, paddy field controlled drainage (PFCD) is applied as an important and efficient approach to agricultural water management. A series of PFCD tests at four major growth stages of rice were conducted by use of 18 lysimeters. Concentration of ammonia nitrogen (NH4+-N) and nitrate nitrogen (NO3--N) in surface and subsurface paddy water was observed. The results indicated that the concentration ofNH4+-N andNO3--N in paddy water declined with the persistence of a waterlogged condition. Compared to traditional drainage, PFCD reduced N loss in surface water by 95.6%, 78.7%, 59.6%, and 87.4% at the stage of tillering, jointing-booting, heading-flowering, and milking, respectively. It should be noted that loads of N losses in surface water increased on the fourth day after waterlogging at the jointing-booting and milking stage, and surface water exhibited higher N concentration on the first day after waterlogging at each stage. Therefore, paddy field surface water drainage should be avoided in these periods.

Agricultural water level control is the key to the combined control of water-saving irrigation and controlled drainage. It is easy to observe and master in farmland practice, and has important theoretical and practical significance. In this paper, a systematic study on stomatal regulation and photosynthetic-evapotranspiration coupling mechanism, as well as the effect of meteorological environmental factors on photosynthetic-evapotranspiration coupling mechanism of paddy rice in drought and flooding conditions was conducted by taking paddy field’s water level as a regulation indicator of paddy rice’s irrigation and drainage. Results showed that net photosynthetic rate (Pn) and evapotranspiration rate (Tr) had quadratic and linear relationship with stomatal conductance (Gs), respectively. The responding range of Gs in drought condition was lower than that in flooding condition. Drought stress aggravated the photosynthetic stomatal limitation of rice leaves at noon, and partial closure of stomata was the main reason resulting in the reduction of Pn suffering from drought at noon. Change curve of paddy rice’s leaf temperature difference (ΔT) showed a W or V type daily change curve and its change rule was rightly contrary to that of Tr. Pn had quadratic curve relationships with photosynthetically active radiation (PAR) and surrounding CO2 concentration (Cs) both in the morning and in the afternoon, Pn had quadratic curve relationships in the morning and linear relationships in the afternoon with air temperature (Ta), respectively. Tr showed linear relationships with PAR, Ta, relative air humidity (RH) and barometric pressure saturation deficit (VPD).