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Fluid Journal : Fluid Journal 1996-1998
3 Fluid Journal Fall 1996 Figure 5. Net return from investment in P and K applied on alfalfa; three-year Utah study. 5 0 229 lb/A 229 lb/A +KO 480 lb/A 2 229 lb/A +KO 480 lb/A 2 229 lb/A +KO 480 lb/A 2 229 lb/A *Total hay value minus fertilizer cost Hay@ $90/ton; P O @ 25¢/lb; K O @ 15¢/lb 25 2 229 lb/A 0 100 200 Dollars/A 300 400 Fertiliz er Cost Added net value* 0 PO 25PO 25 PO 25 PO 25 PO 25 PO 25 Yield, tons/A 10 15 20 effective root zone throughout the growing season. Each ton of hay removes 15 lbs of P2O5. Shortages of P are more likely to occur during: • early growth when rooting is limited • cool periods when P uptake is less • drought, when some of the root zone is dry. Ideally, soil testing of P should be performed prior to planting so the P can be incorporated into the soil when applied. Established stands can be top- dressed with good results, although initial plant response may be delayed if deficiency is severe. The benefits of proper P fertilization are the same as those of K. Yellowing Yellowing of the top leaves is one sure sign of boron deficiency in alfalfa. Other symptoms include death of the growing tip and a bushy appearance. Boron is involved in cell division, pollination, and cell wall synthesis in alfalfa plants. When deficient, the plant's growing points shut down. Death is inevitable if the deficiency persists. By its nature, boron is used up quickly by plants. It leaches through coarse soils. Studies have shown that of total boron in the soil, only .05 to 2.5 percent is available to plants. Boron deficiency can occur in times of drought. It is also sensitive to pH, with increased frequency of deficiency above pH 7. Where crop requirement is high, such as in the case of alfalfa, and soil tests on boron are low or very low, recommended rate of boron application per acre is 2 or 3 pounds. Bottom line At one study site in Utah, the benefits of proper fertilization of alfalfa were shown in hard dollars and cents (Figure 5). Both potassium and phosphorus were used in this three-year project. Symptoms of both P and K deficiencies were present in these fields but were not dramatic and could have been easily overlooked by a busy grower. Returns from this study were impressive indeed. An investment of $57.25 in P brought a net return of $338.75! But total profit per acre was highest with a combination of needed P and K. Had it been put on the market over the three years of the study, 100 acres of alfalfa would have netted $37,475 from a combination of P and K, compared to $33,875 with P alone (Figure 5). The bottom line? Balanced nutrition and proper management of all other inputs will assure maximum nutrient- use efficiency and offer opportunities for significantly more profit in the production of alfalfa! The FFF is grateful for the cooperation of the PPI in the assembling of this article.
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