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  Gypsum Application Technology Study Year 1 ­ 1996
by
D. Zoldoske, R.K. Striegler, and G.T. Berg

CATI Publication #970602
© Copyright June 1997, all rights reserved

The study is being conducted in a Thompson Seedless vineyard located on the Cafifomia State University, Fresno, farm laboratory. The vines were planted in 1980, and are spaced 7 feet by 12 feet. The vineyard utilizes drip irrigation; water is provided by the Fresno Irrigation District and is stored in a reservoir adjacent to the vineyard.

New drip irrigation tubing was installed prior to the start of the 1996 season. Netafim Ram, pressure compensating inline emitters spaced at 42 inches, deliver 0.4 gallons per hour per emitter, or 0.8 gallons per hour per vine.

Treatments consist of surface applied gypsum, drip injected gypsum, and control with no treatment. In the surface applied gypsum treated areas, 1.15 pounds of gypsum was applied by hand directly below each ermitter. The drip injected gypsum treatment area received gypsum directly into the irrigation water with a skid mounted tank and pump provided by Soil Solutions Corporation. The solution grade gypsum is injected daily at a rate of 640 pounds per acre-foot of irrigation water.

Treatments began on June 24, 1996, and continued through October 4, 1996. Irrigations and gypsum were applied on a daily basis. Data collected includes yield, fruit composition, petiole nutrient content, pruning weights, and infiltration rate of the sofl. The experiment will be run in 1997 according to the same protocol.

Table 1. Effect of gypsum application method on Yieldz of Thompson Seedless Grapevines, 1996. California State University, Fresno campus vineyard.
Treatment Yield (lbs/
vine)
Yield (tons/
ac)
Clusters per
vine
Cluster weight (lbs) Berry weight (g) Berries
per cluster
Control -
no gypsum
17.8 4.6 19 0.90 2.0 204
Surface applied gypsum 17.7 4.6 23 0.74 1.8 188
Drip injected gypsum 24.6 6.4 24 1.01 2.1 215
  n.s.y n.s. n.s. n.s. n.s. n.s.
z Harvested on August 13, 1996.
y n.s.=not significant.

Table 2. Effect of gypsum application method on fruit compositionz of Thompson Seedless Grapevines, 1996. California State University, Fresno, campus vineyard.
Treatment Soluble solids (%) pH Titratable acidity (g/100 ml)
Control - no gypsum 22.0 3.58 0.47
Surface applied gypsum 22.3 3.52 0.49
Drip injected gypsum 22.7 3.61 0.43
n.s.y n.s. n.s.
z Sampled on August 13, 1996.
y n.s.=not significant.

Table 3. Effect of gypsum application method on petiole nutrient contentz of Thompson Seedless grapevines, 1996, California State University, Fresno campus vineyard.
Treatment NO3-N (ppm) P (%) K (%) Mg (%) Ca (%) Zn (ppm) Mn (ppm) Fe (ppm) Cu (ppm) B (ppm)
Control - no gypsum 612 0.28 1.39 0.94 0.44 34 170 12 7 27
Surface applied gypsum 475 0.29 1.20 0.96 0.46 35 113 10 6 24
>Drip injected gypsum 480 0.32 1.22 0.95 0.40 31 172 12 6 25
  n.s.y n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s. n.s.
z Petioles collected at full bloom May 7, 1996.
y n.s.=not significant.

Table 4. Effect of gypsum application method on growthz of Thompson Seedless grapevines, 1996. California State University, Fresno campus vineyard.
Treatement Pruning weight (lbs./vine) Nodes retained per vine
Control - no gypsum 5.4 88
Surface applied gypsum 4.4 83
Drip injected gypsum 6.1 83
  n.s.y n.s.