Agricultural Water Use and Technologies for Adaptations to Water Deficits

Abstract

The water withdrawals for agriculture across the United States account for 25–50%, unlike in the dry regions of the world this proportion can be >75–90%. About 57% of the total irrigated acreage in the US is in six states (California, Nebraska, Texas, Arkansas, Idaho, and Colorado), with the remaining states accounting for only 43% of the irrigated acreage. Western states represent the high percent of farmland under irrigation, i.e. 25–40% with some areas >40%. Surface water accounts for a larger portion of total irrigation water withdrawals in the western states, unlike the mid-western and the southern states where groundwater is the major source of irrigation water. The northeastern states show mixed trend, with both surface and groundwater contributing for irrigation water withdrawals. Real time, automated measurement of soil water, temperature, and electrical conductivity in the soil profile, within and below the root zone, is a critical component of best management of nutrients and irrigation aimed to optimize nutrient and water uptake efficiency while minimizing potential leaching of nutrients and water below the root zone. A case study described in this paper was conducted in a potato (cv. Umatilla Russet) and corn field on Quincy fine sand (mixed, mesic, Xeric Torripsamments) under center pivot irrigation in eastern Washington State. Annual precipitation in this region is about 160 mm with only 20% of this amount received during the growing season, i.e. May through August. Therefore, careful management of irrigation is critical to enhance water use efficiency and water productivity. Sensors were used for automated monitoring of soil water content, temperature, and electrical conductivity on a real-time basis at different depths in the soil profile to represent root zone (0–60 cm) and below the root zone (>60 cm). The utility of real time monitoring of soil water data for developing the irrigation set points to maintain the soil water content in the root zone within the management allowed deficit (MAD) to mitigate any impact of water stress while minimizing the water percolation below the root zone are discussed. Similar technologies using user friendly but low cost sensors have been tested in small farms in India (Punjab and Haryana) over the past year. The sensors use capacitance to determine volumetric soil water content in the root zone (0–30 cm). Farmers were advised on the soil water threshold values to be maintained for different crops (spinach, okra, cauliflower, bitter gourd, and rice). While these sensors resulted in initial high adoption of 80% of advisories, the efficacy was reduced after a short period. A new technology, where the sensors automatically control irrigation set points is now being tested. Initial feedback suggests that farmers have a greater level of confidence in the automation, leading to increased and longer adoption rates. This technology is now being tested in only a few sites; will be expanded across three more states in India.