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Low quality water has been widely used for irrigation all over the world due to water shortage. However, the use of low quality water may cause accumulation of salt in root-zone soils, resulting in poor nitrogen utilization by crops. The objective of the present study was to investigate the effects of sodium chloride (NaCI) on mineralization and nitrification of soils in the North China Plain (NCP). The experiments were conducted with laboratory incubators at 30CC. Five levels of NaCl-salt concentrations 0%, 2%, 3%, 5% and 8% in the added solutions were used in the soil samples collected from NCP. The mineralization at NaCl-salt concentration lower than 3% was not significantly different from that of the control, whereas, significant inhibition of mineralization was found in the treatments with NaCI-salt concentration higher than 3%. The inhibition of mineralization was attributed to the retardation of nitrification in relatively high salt content because ammonification was not depressed by the added NaC1 salt. The gas losses and nitrification were found decreasing with the increase in salinity. It was also found that the nitrification was more sensitive to salinity than the mineralization. Nitrification of soil samples was inhibited by 44.72%, 57.87%, and 83.64% compared with the control after 38 days of incubation at NaCI-salt concentrations of 3%, 5% and 8%, respectively. The time dependence of both the mineralization and nitrification can be fitted into a first-order kinetic model. The rate constant of mineralization and nitrification decreased exponentially with the salt content in the soils. The results of the present research may provide some scientific implications for the use of saline water or treated sewage water in the farming regions of the NCP. [ABSTRACT FROM AUTHOR]

In this study, seven widely used potential evapotranspiration (ETo) methods were evaluated by comparing with the FAO-56 Penman-Monteith method (PM method) to provide useful information for selecting appropriate ETo equations under data-limited condition in Beijing, China. Statistical methods and parameters, namely linear regression, root mean squared error (RMSE) and mean bias error (MBE), were used to evaluate the seven ETo methods. Results showed that ETo estimated using Kimberly-Penman method have fairly close agreement with the PM method (referring to standard ETo), considering the coefficient of determination (R²) of 0.96, RMSE of 0.42 mm/day, and a coefficient of efficiency (E) of 0.96. Locally calibrated Penman and Doorenbos-Pruitt methods also have better agreement with the PM method, correspondingly with R² of 0.99 and 0.95, RMSEs of 0.24 mm/day and 0.21 mm/day, and coefficients of efficiency of 1.02 and 0.99, respectively. The ETo is the most sensitive to vapor pressure deficit (VPD) and net radiation in the Beijing area. Hence, the VPD-based and VPD-radiation combined ETo methods were developed and calibrated. Results showed that the two developed methods performed well in ETo estimation. By fully considering the data-limit situation, the calibrated Turc method, VPD-based method and VPD-radiation-combined method may be attractive alternatives to the more complex Penman–Monteith method in Beijing. [ABSTRACT FROM AUTHOR]