Diurnal Soil Water and Root Water Uptake/Nitrogen Dynamics in the Wastewater-Irrigated Pepper Field

To study the effect of wastewater irrigation in pepper fields, this research analyzed the principle of the water vapor–heat–nitrogen coupling transport and the diurnal rule of root water/nitrate uptake dynamics in wastewater-irrigated pepper fields. In an outdoor experiment, the soil water content, negative pressure head, and temperature at depths of 10, 25, 40, 55, and 70 cm were measured hourly for 480 h in July 2013. The modified HYDRUS-1D code was used to analyze soil water and root water/nitrogen uptake dynamics. The numerical analyses provided insight into the diurnal movement of the soil water and root water/nitrogen uptake dynamics driven by the gradients of the pressure heads and temperatures. The measured and simulated data agree well with each other. When the original nitrate-nitrogen (NO₃-N) content in the soil is high, additional wastewater irrigation will not increase the root uptake of NO₃-N. Thus, excessive wastewater irrigation may cause groundwater nitrogen contamination.