Deficit irrigation of alfalfa as a strategy for providing water for water-short areas

Alfalfa is Californiaʹs single largest agricultural water user due to its large acreage and long growing season, using 490,000 to 677,000 ha-m of water each year. Because of the high water usage, interest exists in midsummer deficit irrigation (no irrigation in July, August, and September) of alfalfa to provide water for transfer from water-rich areas such as the Sacramento Valley to water-short areas such as the San Joaquin Valley and southern California with the amount of transferred water equal to the difference in the evapotranspiration (ET) between fully irrigated and deficit irrigated alfalfa. This project investigated the effect of deficit irrigation of alfalfa on yield and ET. Yield and evapotranspiration were measured in fully and deficit irrigated areas of commercial alfalfa fields using the eddy covariance energy balance method in the fully irrigated part and the surface renewal energy balance method in the deficit irrigated part. Alfalfa yield, applied water, canopy coverage and plant height were measured in both areas of the field. Deficit irrigation in July and August reduced alfalfa yields by 4.68–6.47 Mg ha−1. Seasonal ET ranged from 1249 to 1381 mm. Differences in ET between fully irrigated and deficit irrigated alfalfa ranged from 224 to 239 mm. Yields of the deficit irrigated area recovered during the subsequent crop.