Investigating the Impact of Restricted Irrigation Practices on Soil Moisture Variability and Distribution in a Dry Farmed Vineyard Site, Boise, Idaho

Changing climate in semiarid regions may result in increased water stresses for agricultural production, as timing and form of precipitation may result in diminished surface water for irrigation. To prepare for these changing conditions, studies are being conducted on the possibility of dry farmed agriculture as an alternative to irrigated production. This study specifically investigates the ability to grow productive wine grapes with limited or zero irrigation in the Boise Front Foothills, West Foothills TIC Vineyard, located in a climate zone receiving less than 300 mm of annual precipitation. Traditional vineyard performance factors such as planting densities, soil type, rootstock, and climate are standardized and serve as constants in this study. Thus, the limiting factor for vine performance is irrigation. Water delivery through drip emitters varies in each of the three test plots in the vineyard. Soil moisture is monitored at depths of 0.25 meters and 0.50 meters in two pits in each of the test plots. Prior to start of irrigation in June 2011, the sensors recorded the natural variability of moisture resulting solely from precipitation and evapotranspiration. From June on, drying trends are visible in all the data as they start to stabilize at lower moisture levels in July. After weekly irrigation started in June, soil moisture data showed no marked increase from irrigation input. This suggests that irrigation may have a limited role in moisture variability at this distance from the plants. The irrigation may only be affecting the soil moisture at a very localized zone around the emitter and plants. Vine performance is monitored through vine mortality within each test plot throughout a two year period. The results of this study will ultimately demonstrate if non-irrigated farming is a possibility in a dry microclimate