Seasonal Soil Water Content Distribution in Vitis Vinifera (cv. Cabernet Sauvignon) and Vitis Labrusca Bailey (cv. Concord) Vineyards Under Drip Irrigation.

Seasonal irrigation is vital to sustainable production of wine grapes in inland Washington. However, irrigation regimes can vary dramatically between different varieties and species. Red wine grapes such as ‘Cabernet Sauvignon’ are typically managed using regulated deficit irrigation, while juice grapes such as ‘Concord’ are watered heavily. This results in significant differences in soil water content and availability. This project evaluates the effects of several regulated deficit irrigation treatments on soil water distribution throughout the growing season in both ‘Cabernet Sauvignon’ (CS) and ‘Concord’ grape (CG) drip irrigated vineyards.

Our plots are located at a commercial vineyard in adjacent blocks. The CS vineyard is managed with severe regulated deficit irrigation. The treatments were slight increases the water application at different periods of vine development. The CG treatments were limited to between the growth stage between bloom and veraison, with treatments based on evapotranspiration (ET_c) which was calculated using a specific crop coefficient. These treatments resulted in a large reduction in water applied as compared to the grower control treatment.

Soil moisture was measured with a neutron probe at 15 cm increments to 135 cm within 24 hours of an irrigation event throughout the growing season. Additionally, soils were extensively sampled for gravimetric moisture content around vines in the different treatments at three growth stages to determine seasonal soil moisture distribution. The measurements indicated that a period of deficit irrigation greatly effects the distribution of soil water content over the growing season. Soil water content was concentrated within 50 cm of the drip emitter and along the vine-row. Also, there was a sharp decrease in soil water content in the CG vineyard during the treatment period, but water content was restored to pre-treatment levels quickly after treatments ended.