Root Distribution of Mature `Thompson Seedless' (Vitis vinifera L.) Grapevines under Aboveground Drip, Subsurface Drip, and Furrow Irrigation

Abstract

Using subsurface drip irrigation (SDI) is increasing in California vineyards. Reports from growers indicate increased yield, increased water-use efficiency, enhanced soil pest control, and reduced canopy disease pressure for SDI when compared to aboveground drip irrigation (AGDI). However, little information is available in the literature regarding this relatively new irrigation technology for grapes and other perennial crops. A long-term trial was established to evaluate the performance of AGDI and SDI in a mature `Thompson Seedless' raisin vineyard. Portions of a furrow irrigated vineyard block were converted to AGDI and SDI before budburst in 1993. Vine performance, water use, and irrigation system performance data are being collected. As part of this trial, changes in root distribution were examined after harvest in Nov. 1995. Treatments included AGDI, SDI, and furrow irrigation. Root distribution was quantified using the trench profile method. Trenches were opened perpendicular to the row and ≈30 cm from the vine. Roots were mapped along the profile wall using a 1 × 1 m frame, which was divided into one hundred 10 × 10 cm sections. Roots were counted and categorized into four size classes: small (<2 mm), medium (2 to 5 mm), large (5 to 12 mm), and very large (>12 mm). Root distribution differed significantly for AGDI, SDI, and furrow irrigation. The type of irrigation used had the greatest impact on small roots. SDI had more small roots and total roots than AGDI or furrow irrigation. High root densities were observed near the emitter under AGDI and SDI. In addition, both drip irrigation treatments had higher root density near the soil surface than furrow irrigation. Root intrusion was not observed in the SDI treatment.