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Fluid Journal : Fluid Journal 1996-1998
1 Fluid Journal Fall 1998 Summary: Tests run since 1992 have shown the benefits of foliar-applying potassium (K) on cotton plants in the San Joaquin Valley. Greatest increases in lint yield resulted from applications beginning two weeks after first bloom. Foliar K applications later in the season produced less response. The effect was similar regardless of the K source.The application of foliar nitrogen (N) and potassium (K) to cotton at or near the early bloom stage of growth, when these nutrients are needed most, has gained in popularity in recent years. These, and other cultural changes, have resulted in annual yield increases of 32 pounds of lint/A/yr from 1983 through 1996. Widespread K deficiencies have been documented throughout the San Joaquin Valley of California. It has been speculated that these K deficiencies are related to the introduction of high-yielding, early maturing, fast-fruiting cotton varieties. These deficiencies cannot always be corrected by applying K to the soil. However, foliar applications of K may allow correction of these deficiencies more quickly and efficiently. They can allow deficiencies, as indicated by petiole analyses, to be corrected in time to prevent yield loss during the current season. Soil-applied K at this time would be too late, and effective only for the next crop season. Dr. Bill Weir Foliar Potassium Bumps Cotton Yields California researcher reports consistent yield increases to foliar-applied po- tassium over a period of years in the San Joaquin Valley. 0 0 20 40 60 80 100 120 140 Lbs/A 1 Weeks after first flower 2 3 4 5 6 7 Figure 1. Typical response curve of K foliar materials applied to cotton after first bloom, Weir, University of California. Potassium can be required at rates of 1.9 to 3.0 lbs/A/day during the boll fill period of a cotton crop. California studies have demonstrated that K uptake requirements can be difficult to maintain, especially on vermiculitic soils. The amount of fixed K in these soils is great due to high buffering capacities. San Joaquin Valley cotton growers are very aware of the need to be efficient with fertilizer use and to prevent losses of nutrients to groundwater and the atmosphere. Innovative methods of fertilizer applications such as split sidedress, water run, and foliar are becoming common. The increasing interest in supplemental applications of N and K as foliar fertilization by cotton growers presents a unique challenge to researchers. Meeting challenge In 1992, field tests were conducted in Merced County, California, in which K was applied in foliar sprays at various times during the growing season. Positive responses were obtained. As a result, other field tests followed during subsequent years (1993-97). From two to five tests were conducted each year using various carriers of K and different times of application. Plots were sprayed by a tractor sprayer set up for foliar work. It sprayed eight 30-inch rows at a time. Plots were
Fluid Journal 1993-1995
Fluid Journal 1999-2001