|Ayars, James - Jim|
Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/19/2004
Publication Date: 6/1/2005
Citation: Williams, L.E., Ayars, J.E. 2005. Water use of thompson seedless grapevines as affected by the application of gibberellic acid (ga3) and trunk girdling - practices to increase berry size. Agricultural and Forest Meteorology Conference Proceedings. Vol. 129, pgs. 85-94. Interpretive Summary: The increased demand for water outside of agriculture has prompted studies on perennial crops to determine crop water use and the effect of agronomic practices on crop water use. This study determined the effect on water use by Thompson Seedless grapes that were girdled and sprayed with gibberellic acid or just girdled. The water use was determined using a large weighing lysimeter located at the Kearney Agricultural Center in the San Joaquin Valley of California. Water use was reduced by the girdling and the use of gibberellic acid compared to the non-girdled vines. The Kc value of the girdled vines was reduced compared to the non-girdled vines which will result in a lower water use when applied to an irrigation schedule. It was also determined that the Kc value does not decrease late in the season if the crop is fully watered and pests are controlled. There are opportunities to reduce water use by the careful management of irrigation following harvest but these will require additional study.
Technical Abstract: Seasonal water use of Thompson Seedless grapes was determined with a large weighing lysimeter in the San Joaquin Valley of California from 1994 to 1996. During the first year of the study , the vines growing within the lysimeter were treated as would be done to produce fruit for use as table grapes; the application of gibberellic acid and trunk girdling a berry set. Both practice will increase berry size of this seedless cultivar. In 1995, the vines in the lysimeter were only girdled at berry set, no application of gibberellic acid at that time. Reference crop evapotranspiration between March 15th and the end of October averaged 1124 mm across the 3 years. Water use shortly after the vines were girdled in 1994 increased as would be expected for non-girdled grapevines while in 1995 water use after girdling decreased for a period of approximately 4 weeks. Once the girdles healed in 1995 water use increased to values similar to those of the previous years. The crop coefficient (Kc) subsequent to girdling in 1994 remained constant for a period of 4 weeks while the Kc decreased after girdling in 1995. The Kc increased after the girdles healed both years and remained at a value of approximately 0.9 until the end of October. In 1996, the vines in the lysimeter received none of the treatments used in the previous 2 years. The seasonal water use and maximum daily water use in 1996 of the vines in the lysimeter were greater than in 1994 and 1995. Water use in vines was equivalent 838, 708, and 936 mm from March 15 until the end of October while the reference ET was 1136,1060, and 1176 during the same period in 1994, 1995, and 1996, respectively. At full canopy in 1996 the Kc leveled off at a value of 1.1 and remained such until the end of October. The results indicate that girdling the trunks of grapevines can affect water use when compared to non-girdled grapevines. Additionally, the Kc of this perennial horticultural crop does not decrease after harvest on later in the season if the vines are fully irrigated and insect pests are controlled.