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Accurate modeling of soil water content is required for a reasonable prediction of crop yield and of agrochemical leaching in the field. However, complex mathematical models faced the difficult-to-calibrate parameters and the distinct knowledge between the developers and users. In this study, a deterministic model is presented and is used to investigate the effects of controlled drainage on soil moisture dynamics in a shallow groundwater area. This simplified one-dimensional model is formulated to simulate soil moisture in the field on a daily basis and takes into account only the vertical hydrological processes. A linear assumption is proposed and is used to calculate the capillary rise from the groundwater. The pipe drainage volume is calculated by using a steady-state approximation method and the leakage rate is calculated as a function of soil moisture. The model is successfully calibrated by using field experiment data from four different pipe drainage treatments with several field observations. The model was validated by comparing the simulations with observed soil water content during the experimental seasons. The comparison results demonstrated the robustness and effectiveness of the model in the prediction of average soil moisture values. The input data required to run the model are widely available and can be measured easily in the field. It is observed that controlled drainage results in lower groundwater contribution to the root zone and lower depth of percolation to the groundwater, thus helping in the maintenance of a low level of soil salinity in the root zone. [ABSTRACT FROM AUTHOR]

Brackish water has abundant reserves and high utilization potential in agriculture. Clarifying the soil carbon (C) and nitrogen (N) mineralization characteristics during different periods under irrigation water salinity conditions is of great significance for seeking a brackish water irrigation method for soil nutrient supply and maintenance. In response to this, incubation experiments were conducted to study the effects of irrigation water salinity (1.1, 2.0, 3.5, and 5.0 g/L) on C and N mineralization under conditions of constant temperature and freezing-thawing cycle. The results showed that the increasing irrigation water salinity reduced soil organic carbon (SOC) and total nitrogen (TN) content, SMBC and SMBN content, decreased soil urease and invertase activities, and had a negative impact on soil fertility. Under constant temperature conditions, increasing irrigation water salinity inhibited soil C and N mineralization by reducing soil urease activity, SOC and TN content. Under the conditions of freezing-thawing cycle, increasing irrigation water salinity promoted soil C and N mineralization by increasing soil salt content. When using brackish water for irrigation in the field, it is necessary to avoid using high salt content brackish water for irrigation to avoid insufficient soil nutrient supply during the growth period. Autumn irrigation measures should be taken in a timely manner before the freeze-thaw period to wash out the salt in the soil to avoid soil nutrient loss after the freeze-thaw period. [ABSTRACT FROM AUTHOR]