Irrigation of alfalfa and pasture requires large quantities of water and is sometimes considered a contributor to low flows in the Scott River. A 3-year study was conducted to evaluate the potential for agriculture water conservation in Scott Valley. The effect of irrigation termination date on forage production was evaluated to determine how late in the season irrigation is needed. The soil moisture status of several irrigated pasture and alfalfa fields was monitored weekly for the duration of the growing season using resistance blocks and a neutron probe. This permitted an evaluation of the adequacy of current irrigation practices.

The different irrigation cut-off treatments had a profound effect on soil moisture levels. However, only the early irrigation cut-off treatments, July to mid August, caused an appreciable reduction in alfalfa yield. There was no need to irrigate after the final alfalfa cutting for the soil type studied. The date of the final irrigation of the season had no effect on alfalfa yield the following season. Late-season (October) pasture yield was affected by irrigation termination date. There was little to no difference in yield between the latest two irrigation cut-off dates. Pasture species were more sensitive to moisture stress than was alfalfa. The earliest irrigation cut-off date, August 3'd, killed some grass plants and reduced yield the following year.

The monitoring study indicated that soil moisture content fluctuated considerably during the growing season. Periods of low soil moisture were generally associated with harvests, a time period when fields cannot be irrigated. The soil moisture content was typically lowest in mid to late summer between irrigations and, in the case of alfalfa, in fall after the final harvest of the season was made.