Soil Erosion Prediction on Irrigated Lands: State of Science, Challenges and Outlook

Abstract. About half (or $106.3 billion in 2012) of the market value of crops sold in the United States is produced on irrigated farms with most of these farms located in the 17 western states. This significant contribution to U.S. agricultural output contrasts with the modest proportion of total farmland area covered by irrigation. In 2018, only 55.9 million acres of the 899.5 million acres of U.S. farmland were irrigated (USDA-NASS, 2019), illustrating the significant role played by irrigation in agricultural market value in the U.S. Water availability both in quantity and quality is the primary concern in many regions where irrigated agriculture is dominant. Irrigation is the largest consumer of freshwater resources (118 of 281 billion gallons per day in 2015) in the U.S., closely followed by thermoelectric power (95.1 billion gallons per day in 2015) (Dieter et al., 2018). In addition to resource concerns common to rainfed agriculture (e.g. ground and surface water quality, soil resilience, air quality, etc.), irrigated agriculture must also consider resource issues inherent to irrigation water usage (e.g., aquifer depletion). Projected increases in food and water demands due to population growth creates a complex environmental context in which more food will need to be produced for every unit of water extracted for irrigation while impacts on other natural resources are minimized at the same time. Most of U.S. irrigated lands lie in arid or semi-arid regions where natural ground cover is low and soils are highly vulnerable to wind erosion. Soil erosion by water is also a major concern on irrigated lands, especially in areas where surface irrigation (e.g., furrow irrigation) is used (King et al., 2016). Pressurized systems (sprinkler irrigation) have historically been proposed as more efficient alternatives to gravity systems with documented benefits in water consumption (Sammis, 1980) and inferred off-site water quality. The effect of management with pressurized irrigation systems on soil erosion and nutrient transport is however poorly understood due to a historical lack of research on the topic. Furthermore, innovations in irrigation systems will continue to produce new technologies that will need to be evaluated for their performance in optimizing productivity and sustainability on farms where they are adopted. Future challenges that need to be addressed to improve soil erosion prediction on irrigated lands include: (1) establishment of the link between irrigation water chemistry and erosivity, (2) the development of accurate erosion prediction equations that take into consideration irrigation types (furrow, flood, center pivots, wheel lines), and (3) the development of a modeling framework capable of adapting to future advances in irrigation technologies.