| In recent years, livestock and poultry breeding industry has developed rapidly but generate a great amount of wastewater. Compared with directly discharging into earth's surface or groundwater body, using the wastewater for farm irrigation is the most effective way of resources recycling. Swine wastewater, irrigated back to the farmland, not only provides water for the crop, but also is a good fertilizer source. On the basis of field tests, seeking for the effect of different irrigating amount and period on crop yield in winter-wheat and summer-maize rotation system, conventional methods are expensive and time consuming. In this study, the Root Zone Water Quality Model (RZWQM) was used to overall evaluate the effects of irrigating amount and period on soil-plant system.Field experiments were carried out from September, 2007 to September, 2008, in Yililai breeding farm of Yang Liuqing Town, Xiqing District, Tianjin. First, the model was calibrated using the data of volumetric water contents in the soil profile, nitrate-N contents, crop production of the Tanae:gw1:1 treatment(quota=830 m3 ha-1), then the model was validated with the data of the TManae(quota=500 m3 ha-1)and Tanae:gw1:5 treatment (quota=830 m3 ha-1). Finally, based on the calibration and validation, optimizing wastewater amounts and periods with RZWQM, relatively better irrigation modes of the simulated year were got.Through the course of simulation and prediction, the results were shown that simulated values of soil water reflected the variation tendency of measured values on the whole, 0-60 cm soil layer was better. And simulated values of nitrate-N contents in each layer of soil profile basically reflected the variation of measured values. The simulated result of the TManae treatment was better in the three treatments. The simulated results of nitrate-N cumulants in the 0-100cm soil layer in different growth periods of each treatment were relatively better. The simulated yields of winter-wheat and summer-maize were in good consistence with the measured ones, with RE basically controlled into±16% interval. The simulated values of maize aboveground biomass were unanimous with the measured ones, but the simulated values of wheat aboveground biomass were less than the measured ones. Towards different irrigation combinations, several better irrigation modes were got as follows: (1) Irrigate with the anae:gw1:5 water, two irrigations with irrigation quota of 830 m3 ha-1 for the winter wheat at wintering stage and jointing stage respectively could obtain 5625 kg ha-1 for winter wheat and 8403 kg ha-1 for summer maize, the content of nitrate-N in 0-100 cm soil layer was 85.18 kg ha-1 after corn harvest; (2) Irrigate with anae:gw1:1 water, groundwater irrigation quota of 830 m3 ha-1 for the winter wheat at wintering stage and heading stage respectively, 700 m3 ha-1 anae:gw1:1 water only at jointing stage also could obtain 5625 kg ha-1 for winter wheat and 8403 kg ha-1 for summer maize, the content of nitrate nitrogen in 0-100 cm soil layer was 97.20 kg ha-1 after corn harvest; (3) for omitting the trouble during the course of dilute anaerobic water, groundwater irrigation quota of 830 m3 ha-1 for the winter wheat at jointing stage and heading stage respectively, and 300 m3 ha-1 anaerobic water only at wintering stage; or groundwater irrigation quota of 830 m3 ha-1 for the winter wheat at wintering stage and jointing stage respectively, and 400 m3 ha-1 anaerobic water for irrigation only at heading stage, both of the above two schemes could obtain more yields. After corn harvest, nitrate-N contents in 0-100 cm soil layer were also in permitted extent of environmental safety. Overall, RZWQM was applicable of simulating the effect on crop production, water contents and nitrate-N contents in soil profiles under swine wastewater irrigation. Meanwhile, the model was also used to exactly predict the influence of irrigating amount and period on crop yields and nitrate-N contents in the soil.
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