Two-dimensional modeling of nitrate leaching for various fertigation scenarios under micro-irrigation

The regular application of nitrogen fertilizers by irrigation is likely responsible for the increase in nitrate concentrations of groundwater in areas dominated by irrigated agriculture. Consequently, sustainable agricultural systems must include environmentally sound irrigation practices. To reduce the harmful effects of irrigated agriculture on the environment, the evaluation of alternative irrigation water management practices is essential. Micro-irrigation offers a large degree of control, enabling accurate application according to crop water requirements, thereby minimize leaching. Furthermore, fertigation allows the controlled placement of nutrients near the plant roots, reducing fertilizer losses through leaching into the groundwater. The presented two-dimensional modeling approach provides information to improve fertigation practices. The specific objective of this project was to assess the effect of fertigation strategy and soil type on nitrate leaching potential for four different micro-irrigation systems. We found that seasonal leaching was the highest for coarse-textured soils, and conclude that fertigation at the beginning of the irrigation cycle tends to increase seasonal nitrate leaching. In contrast, fertigation events at the end of the irrigation cycle reduced the potential for nitrate leaching. For all surface-applied irrigation systems on finer-textured soils, lateral spreading of water and nitrates was enhanced by surface water ponding, causing the water to spread across the surface with subsequent infiltration downwards and horizontal spreading of soil nitrate near the soil surface. Leaching potential increased as the difference between the extent of the wetted soil volume and rooting zone increased.