Controlled irrigation and drainage (CID) has received attention for improving water quality. Under CID condition, water stress is frequently experienced in two contexts: first drought and then flooding (FDTF) and first flooding and then drought (FFTD). This study aimed to investigate the effects of FDTF and FFTD on nitrogen (N) and phosphorus (P) dynamics in paddy water at different growth stages. The effects of water stress on the migration and transformation of N and P were also investigated. Results showed that CID can decrease N and P concentrations in surface water.NH4+-Nwas the major form of N in surface drainage and percolation water. Mean total phosphorus (TP),NH4+-N, andNO3--Nconcentrations were significantly higher than in FFTD during the growth stage. MeanNH4+-N,NO3--N, and TP concentrations were significantly higher in percolation water under flooding stress than those under drought stress at growth stage, except for mean TP concentrations at milky stage (stage IV). Meanwhile, flooding can sharply increase theNH4+-N,NO3--N, and TP concentrations in percolation water after drought. Thus, without CID, the considerably highNH4+-N,NO3--N, and TP concentrations via runoff and leaching can be responsible for the eutrophication of water bodies in the vicinity of paddy fields during the rice growing season when water stress transforms from drought into flooding.

Paddy is the most important grain crop in China. In addition, water is one of the most important components for sustainable paddy production, and the quantity of irrigation for paddy fi elds accounts for approximately 70% of its total agricultural water resource consumption [1]. However, water supply is limited because of serious regional and seasonal water shortages, and paddy production is impaired by increasing water shortage [2]. Meanwhile, China is the largest producer and consumer of synthetic fertilizers in the world. Fertilizer and pesticide overuse in order to achieve high paddy yields might result not only in poor grain yield but also low N use Pol. J. Environ. Stud. Vol. 27, No. 1 (2018), 345-355 AbstractAlternate drought and fl ooding stress has become more prevalent during paddy growth stages as a result of climate change, especially in southern China. This study aims to assess the effect of alternate drought and fl ooding stress on water use, and nitrogen (N) and phosphorus (P) losses in paddy fi elds. Two controlled irrigation and drainage (CID) managements (namely drought at the beginning of growth stages followed by fl ooding (CID-1), and fl ooding at the beginning of growth stages followed by drought (CID-2) and one alternated wetting and drying (AWD) management were designed in specially designed experimental tanks with three replications in 2015 and 2016. Results showed that CID increased effective irrigation quantities and rainwater storage ability with a signifi cant decrease in water use effi ciency compared with AWD. For surface water, CID-1 signifi cantly improved possible losses of nitrogen and phosphorus during the fertilizer application period over CID-2. For subsurface water, CID can signifi cantly reduce the leaching losses of nitrate N and P compared with AWD. Meanwhile, CID-1 signifi cantly inc reased the leaching losses of nitrate N at the former two growth stages compared to CID-2, yet no signifi cant difference was found for ammonia N and P. Therefore, the application of controlled irrigation and drainage -especially for CID-1 -was an effi cient method for obtaining high water quality and reducing eutrophication.

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To achieve the dual goal of water conservation and high grain production, agricultural systems must decrease water usage and increase water use efficiency (WUE). In recent years, controlled irrigation and drainage (CID) has been used and developed as a new water-saving technique for paddy rice production. The present study aimed to explore the influence of different CID regimes on the yield, agronomic traits, and WUE of paddy rice. Treatments included alternate wetting and drying (AWD), CID-I (a lower limit of irrigation to 200 mm), and CID-II (a lower limit of irrigation to 500 mm). Plant height increased but tiller number significantly decreased under CID compared with those under AWD. Implementing CID decreased irrigation water volume (IV) by 9.7%-37.1%, which increased yield irrigation water use efficiency (IWUEy) by 14.6%-51.5%. Under CID-I, grain yield decreased by 2.9% in 2015 and increased by 3.5% in 2016. CID-II obtained marginally, but not significantly, lower yields (4.7% in 2015 and 2.0% in 2015) than AWD because the percent of filled grains (PFG) and spikelets per m 2 (SPM) decreased under this irrigation scheme. IWUEy and biomass irrigation water use efficiency (IWUEb) were significantly higher under CID than under AWD. The highest IWUEy and IWUEb were observed under CID-II. Our results indicate that CID can reach a lower limit of irrigation to 500 mm below the topsoil and a ponding water depth of 200 mm after rainfall, with some acceptable yield penalty when water is inadequate and costly.

Controlled irrigation and drainage (CID) has received considerable attention as a reliable management practice for improving water quality and water productivity in rice production. This study aimed to evaluate the effects of CID on water productivity, nitrogen, and phosphorus losses in paddy fields. Treatments include alternate wetting and drying (AWD; lower limit of irrigation to-200 mm and upper limit of ponding water depth after rainfall to 60 mm), CID-I (lower limit of irrigation to-200 mm and upper limit of ponding water depth after rainfall to 200 mm), and CID-II (lower limit of irrigation to-500 mm and upper limit of ponding water depth after rainfall to 200 mm). Results showed that CID reduced irrigation water without a significant impact on grain yields and increased the irrigation water productivity by 14.6-51.5% compared with AWD. However, the percolation of CID may be increased, especially in a wetting year. The application of CID-II by combining yield with irrigation water productivity could be suitable and beneficial to rice crops. The average total nitrogen (TN) and total phosphorus (TP) concentrations of CID presented similar values or were significantly increased relative to AWD, indicating that the significant decreases in nutrient loads under CID were primarily due to reductions in surface runoff rather than changes in concentration. Ammonium nitrogen (NH 4 +-N) concentrations were clearly increased after fertilizer application in percolation water. Compared with AWD, the NH 4 +-N, TN, and TP leaching losses of CID-I were increased. The nitrogen and phosphorus leaching losses of CID-II were significantly increased relative to AWD and CID-I because of high nutrient concentrations and severe preferential flow. Therefore, CID potentially increased nitrogen and phosphorus loading to groundwater