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Fluid Journal : Fluid Journal 2005-2007
EARLY SPRING 2007 Fluid Journal 17 Foliar fertilization is an effective way of quickly supplying plant nutrients during critical periods of flowering and grain fill at which time soil or root conditions are often unfavorable for optimum root uptake and there is insufficient uptake to supply demand. Boron (B) and other micronutrients have been supplied effectively to soybeans by foliar application and, under top management, often provide the limiting nutrient factor for those extra few bushels at the top of the yield curve. Boron is the most widespread high-yield limiting micronutrient. Boron fertilization is known to promote flowering, pollen germination, grain fill, and yield where B is applied near flowering. Boron is essential for all plant growth. Soybeans, like all legumes, have a high B requirement. Boron is necessary for: • Stimulation of root growth • Increased root nodule development for nitrogen (N) fixation • Increased branching and flowering • Increased bloom retention • Increased pod number • Better seed development and grain yield. How it works Foliar fertilization is the practice of applying nutrients for plant leaves through ground or aerial spraying equipment or through Foliar Boron Bumps Soybean Yields Wisconsin, Illinois, Ohio and Missouri field studies show that boron applied at 0.25 lb/A increased yields by 3 percent, overall. without leaf injury at concentrations up to 0.5 percent B in solution, or split into more than one application using lower volume as in aerial application. Low volume sprays with up to 1 percent B concentration may be applied singularly in solution, but there may be risk of leaf burn if other chemicals are applied in the mixture. It is an economical practice to apply B or other nutrients together in a tank mix with insecticides, fungicides, other chemicals. This is a good practice and usually works well, but caution is advised. Mixing. Attempts to apply several chemicals together in a minimum amount of water sometimes produce mixtures that are physically and chemically incompatible. Small quantity tests are advisable when trying new combinations of products. Immobility. Foliar sprays are especially important for those plant species in which B is immobile; B uptake from the soil can be insufficient to supply these plants' needs at critical periods of growth and reproductive development. Soybeans are considered one of the B-immobile species. Timing. Proper timing of foliar sprays is essential to ensure that B is applied when its need is most critical. The B fertilizer must be on site, the sprayer must be ready to go, and procedures should be in place to keep the sprayer operating sprinkler irrigation systems. Even though the rate of nutrient uptake through leaves is somewhat slower than through root pathways, less B (usually half to a fourth as much) is required through foliar application to achieve the same results. Some B studies have shown that foliar-applied B can be 90 percent absorbed within 24 hours of application. Foliar B can be immediately present where needed in the plant at the site of maximum demand and use in plant leaves during the critical times of seed production when movement from soil to root may be inadequate and root activity is declining. Practical considerations How much? Many recent studies have shown that 0.25 to 0.5 lb/A of B is the optimum rate of B application, although responses to multiple sprays totaling 1 lb B/A have been observed. A single foliar spray of 0.25 lb B/A can be safely applied
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