Alfalfa yield and stand response to irrigation termination in an arid environment

Alfalfa (Medicago sativa L.) irrigation is often withheld as a water conservation measure in arid regions. The objective of this research was to test the hypothesis that alfalfa yields and stands can be permanently damaged by withholding irrigation water in arid environments. Irrigation termination studies were conducted on a Superstition sand (sandy mixed, hyperthermic Typic Calciorthid; 95% sand) in Yuma, AZ, and on a Casa Grande sandy loam [coarse-loamy, mixed (calcareous), hyperthermic Typic Natrargid (reclaimed)] at Maricopa, AZ. Irrigations were terminated in the summer (July through October) and winter (November through February) in Yuma and in the summer (August through September) and summer, fall, and winter (August through mid-March) in Maricopa. Summer irrigation termination at the Yuma site reduced stand from 43 to 16 plants m^-2 and reduced hay yield from 1.50 to 0.52 Mg ha^-1 per cutting after irrigation was resumed. Irrigation termination at the Maricopa site was not detrimental to stands, although hay yields per cutting were depressed from 2.90 to 2.52 Mg ha^-1 following the second cycle of summer irrigation termination and from 3.10 to 2.43 Mg ha^-1 following the second cycle of summer through winter irrigation termination. Winter irrigation termination at Yuma had no residual effect on yield or stand. Alfalfa water use was reduced by irrigation termination at Maricopa, even after irrigation was resumed. Total nonstructural carbohydrates in the roots were not consistently higher or lower than the control during irrigation termination. Termination of alfalfa irrigation as a water-conserving measure is not always advisable in and environments due to the possibility of permanent crop damage.