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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Fall 1994 less pronounced. Zinc deficiency appears to retard development and maturation of the heads. Cotton. Delay in flowering. Reduction in boll size. Plant produces only a few squares and sheds them around time of anthesis. Soybeans. Interveinal chlorosis. Necrosis of lower leaves. Poor pod initiation and development. Wheat. Chlorotic and necrotic stripes along each side of midrib. Shortened leaves. Oil-soaked appearance in leaves, followed by collapse of leaves across middle. Behavior in soil One of the natural causes of zinc deficiency is tie-up in high-alkaline soils---that is, calcareous or high-pH soils. Zinc deficiency is also found in soils high in organic matter. Sandy soils, soils high in clay content, and soils naturally high in phosphates (which tend to tie up zinc) are also causes of deficiencies. Surface soils contain a greater proportion of available zinc than subsoils. It is a general belief that surface accumulation of Zn is caused by subsurface mining by plant roots, decay of organic matter, and subsequent deposition at the surface. Cool, wet soils can cause zinc deficiency by reducing root growth. Zinc is very sensitive to cold temperatures. The movement of zinc is slower in acidic soils, which may reduce crop absorption from spatial unavailability. Liming of soils raises the pH and may help eliminate some movement problems, but these gains are usually offset because the higher pH increases soil zinc-fixing capacity, especially in soils high in phosphate. Because of its high insolubility and immobility in the soil, zinc should be applied under the subsoil with a starter fertilizer or by root zone banding. Man-made deficiencies Cultural practices can also cause zinc deficiencies in soils. Fertilization. Heavy applications of phosphate fertilizer several years running can induce a zinc deficiency. Crop uptake is reduced. This may be due to competitive ion effects, fixation of zinc in unavailable forms, or physiological imbalances. Growers should also be aware that N fertilizers can increase crop growth to a point where zinc requirement of plants exceeds availability in soil. Land renovation. Field areas where top soil is removed can cause zinc deficiency because zinc is always concentrated near the surface. Soil compaction. Compacted areas will cause zinc deficiencies because of zinc's immobility---it doesn't move with the soil water. Depletion. High yields and heavy cropping can deplete soils of zinc. Making it pay As stated earlier, proper use of zinc in a fertility program can add substantial bushels per acre. We'll look at several examples. Kansas. In this study, the land was low in P and Zn. Adding 80 lbs/A of a liquid phosphate without zinc actually depressed corn yields when compared to the check, as shown in Figure 1. But correcting the P/Zn imbalance by adding 80 lbs/A of P with 10 lbs/A of Zn boosted yields over check by 62.2 bu/A! A good rule of thumb is: if you're low in phosphorus and low in zinc, apply both in your fertilizer program. Nebraska. The effect of different rates of zinc applied with a fluid starter on corn was shown in this study. Note how one pound of zinc increased corn yields by 29 bu/A over check in 1975 and 77 bu/A over check in 1976 (Figure 2). The crop was grown in an irrigated field on a sandy soil having a pH greater than 7. In another Nebraska study, it has been shown how even an infinitesimal amount of Zn banded near the seed in a fluid starter program can give spectacular responses. Note how only one-tenth of a pound of zinc applied per acre increased corn yield 57 bu/A when compared with check (Figure 3)! A mere dollars worth of zinc placed below and to the side of the seed nearly doubled the yield. Zinc in fluids During the early period when fluid and suspension fertilizers began to gain in popularity, researchers Mortvedt and Giordano reported that ZnO in fluid fertilizers was more effective than ZnO incorporated with granular fertilizer. Distribution was markedly superior in fluids. Other studies in Kansas have shown 12- to 20-bu/A increases in corn yield where zinc was banded with polyphosphates at planting time, versus yield losses when zinc was added to dry fertilizers and broadcast. Superior distribution, placement, and incorporation paid off with an element whose nasty property is high insolubility.
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