Summerfallow generally reaches field capacity during the first fall or spring after harvest. Precipitation that falls after field capacity is reached runs off or percolates beyond the rooting zone. Because fallow fields remain at or near field capacity for an extended period of time, they have a greater potential to allow percolating water and nitrogen beyond the rooting zone, compared to continuous cropping systems. Irrigation Irrigation in North Dakota creates conditions that can carry a higher risk of groundwater contamination compared to dryland farming. Irrigation generally occurs on coarse-textured soils that have good drainage and are prone to leaching.
Irrigation often occurs over shallow aquifers.
Because irrigation increases yield potential, increased nitrogen levels are required to meet that potential. Excessive inputs of either nitrogen or water, particularly on irrigated coarse-textured soils, substantially increase the potential for nitrogen leaching. Sprinkler systems, especially center pivots, allow good water control and less leaching risk. Furrow and flood irrigation systems are the poorest in terms of water application efficiency. Under irrigation, profitable crop production and groundwater protection have been demonstrated when existing guidelines for nitrogen application and water management are followed.