Ali Erfani Agah

By Ali Erfani Agah, Patrick Meire and Eric de Deckere

Today, wastewater irrigation is one of the best options to reduce the stress on limited availability of fresh water and to meet the nutrient requirements of crops. In the present study, the simulation accuracy and performance of the HYDRUS-1D model to predict phosphorus leaching have been evaluated and compared to lysimeter data. More specifically, the effects of irrigation using four types of water (wastewater, effluent, mixture of freshwater and effluent, and freshwater) on three types of soil (sandy loam, loam, and clay loam) have been investigated both experimentally and numerically. Barley was planted as a common agricultural crop. The leachates from lysimeters have been collected and sampled at the beginning, middle, and end of the growing season. These samples have then been analyzed for phosphorous. The results show that the trend of change in nutrient concentration (P) was a function of plant requirement. Maximum process of leaching occurred concurrent with minimum plant requirement. The average phosphorus leaching into the root depths turns out to be insignificant, as it amounts to only 0.65–1.65%. This reassuring result means that wastewater with high concentrations of phosphorus compounds (up to 5–10.3 PO4-P mgl−1) can just be treated through an intermittent application to the land surface. Overall, a good agreement between experimental- and numerical-model results is obtained, wherefore the model overestimates the mean phosphate leaching during the growing season of the crop slightly. On the basis of these results, soil with loamy texture was considered to be the most suitable type for irrigation with wastewater and effluent. The results of this research indicate that with a proper management program in regard to the types of soil to be used, crops to be cultivated, water quality, and timing maneuver, the negative impacts of low quality water on soil/plant/groundwater systems can be minimized.

Part of the book: Soil Contamination

By Ali Erfani Agah

Because of water scarcity, reduction of annual rainfall and the use of wastewater in agriculture, there is a need for research to evaluate the potential impacts of using such sources on hydraulic soil properties and groundwater quality. Nitrate loss from the area under cultivation and regular use of fertilizer and wastewater is a major reason for non-point source contamination on agricultural lands. Numerical model, Hydrus-1D used to simulate soil nitrate in soil cultivated with tomato-crop during the growing period, in North-East Iran. A randomized completely blocked design with five irrigation treatments with different sources of nitrogen was applied. Comparison between simulated and measured soil moisture content shows that the model can follow the temporal variation of soil water content. However, some over estimation of the measured data was observed during the simulation period. To evaluate the Hydrus model performance with respect to nitrogen transport and transformations, the simulated nitrogen concentrations (NH4-N and NO3-N) are compared for different treatments at different depths of soil profile, (7.5, 22.5, 37.5, 52.5 and 120 cm from soil surface). It takes about 4 days to convert 90% of urea into ammonium and it takes about 70 days to convert 90% of ammonium into nitrate. However, urea concentrations decreased with time between irrigations as a result of hydrolysis. As expected, at 3.73 days, the urea was concentrated near the surface, immediately after fertigation. Ammonium remained concentrated in the immediate in the top soil at all times for all treatments. There was only slight movement, because of soil adsorption and subsequent fast nitrification and/or root uptake. In contrast to ammonium, nitrate moved continuously downwards during the 28-day simulation period, as nitrate is not adsorbed, whereas denitrification was assumed negligible. Leaching percentages were smaller for nitrate wastewater compared to nitrate- fertilizer, and manure. Base on simulation results treated municipal wastewater by an aerated lagoon can be used as a valuable source of irrigation without causing contamination of groundwater.

Part of the book: Recent Advances in Numerical Simulations