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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Spring 1995 Foliar. Foliar application of boron effectively increases July leaf boron only in the year of application. Only at very high rates does it carry over into subsequent years. Timing critical Timing of foliar boron spraying is critical, as is readily apparent in Table 1. Late dormant sprays (just prior to bud swell) through to 20 percent bud break are the most effective. Later sprays effectively increase boron levels in the tissue but may not enhance current year fruit yield and quality. Enhanced yield in response to boron sprays may decrease yield in the following off-year, effectively enhancing alternate bearing. At the site used here, boron sprays produced a net yield increase of approximately 20 percent over the two- year period. The effectiveness of early, but not late, boron sprays is further evidence that boron is critical for pollination or fertilization of pistachio flowers. Procedure The experimental site was established in 1989-1990 in boron-deficient sites near Arbuckle, CA. Four fields were used (two for soil applications; two for foliar applications). The experiment was designed as a randomized complete block with 50 replicate trees per block. Over 1,000 pistachio trees were used, divided into four groups. In 1989-90, soil treatments were made in November at rates of 0, 2, 4, 6, and 8 ounces Solubor per tree. Foliar treatments were made in January and again in July at rates of 0, 2, 5, and 10 lbs Solubor/l 00 gals. In the second year of this experiment, one site receiving foliar sprays and two sites receiving soil boron treatments were given no additional applications. This was done to investigate the effectiveness of fertilizer carryover on productivity. The remaining foliar site was sprayed at the late dormant stage, and again in mid-July. In the third year, only one site received foliar treatments in March. In addition, a subset of trees was used for a spray timing trial. In this site, trees were sprayed with 5 lbs Solubor/l 00 gals at either of five dates---from late dormant through full leaf emergence. Total yield was determined on each of 800 trees and related to boron application, pollen growth, and nut quality. Harvested nuts were sorted and the percent of blanks, non-splits, and average kernel weights were determined. Dr. Brown is assistant professor and Dr. Ferguson is extension specialist in the Department of Pomology at the University of California-Davis. Dr. Picchioni is an assistant professor at Louisiana Tech University.
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