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Fluid Journal : Fluid Journal 1993-1995
3 Fluid Journal Spring 1995 0 lbs/A S 10 lbs/A S 20 lbs/A S 160 140 120 100 80 60 Yield - bu/A 0 75 150 N rate - lbs/A raising nitrate concentrations in plant tissue. High nitrate levels, which accumulate when S is deficient, drastically inhibit seed formation in sensitive crops such as canola. Nitrate can also be toxic to animals consuming S-deficient for-ages. Adequate S levels improve Mg digestion in ruminants by reducing for-age (feed) non-protein N levels. Deficiency symptoms Sulfur, like nitrogen, is a constituent of proteins, so deficiency symptoms are similar. N-deficiency symptoms are more severe on older leaves because N is a mobile plant nutrient and moves to new growth. 5, on the other hand, is immobile in the plant, so new growth suffers first when S levels are not adequate to meet crop needs. This difference is important in distinguishing between the two, particularly in early stages of a deficiency. Having set the stage, we'll now explore how to properly identify S deficiencies. Generally, agronomists advise growers to watch for the following signs of S hunger: • small spindly plants with short, slender stalks • retarded growth rate and delayed maturity • light green to yellowish color of leaves, with even lighter colored veins (on most plants, this yellowing shows up first on young, upper leaves, while most N deficiencies show up first on bottom leaves). However, specific symptoms may vary considerably from one crop to another as the following descriptions and accompanying photographs (Figure 2) demonstrate: Corn. S deficiency begins with a marked yellowing along the length of the leaves between veins, particularly on newer, upper leaves. Reddening later occurs at the base of the stalk and along leaf margins. Gradually, the reddening spreads across the leaf to the midrib. Soybeans. To identify S deficiency, watch new leaves for a period of several days. Initially, all new leaves are pale yellow-green, but in a S deficient plant they remain pale. In a healthy plant, they turn dark green. Older leaves may remain dark green longer, but eventually the entire plant turns yellow. Leaf size and length of spaces between nodes are reduced in a deficient plant. Wheat. S deficiency is first seen in a general yellowing of the plant, usually more pronounced between the veins. Older leaves tend to remain green. Alfalfa. S deficiency can be identified by a persistent yellow-green cast to new growth, more erect leaflets, and a reddening of stems. Tillering also is markedly reduced. Clover. In subterranean clover, S deficiency is indicated by general yellowing, although older leaves may turn a pinkish red. Petioles redden and leaflets stand more erect. Cotton. A persistent yellowing of new leaves and reddening of petioles are sure signs of S deficiency. There is little difference in plant or leaf size between S deficient and healthy plants. Peanuts. New leaflets are smaller, paler, and stand more erect from the petiole than normal ones, giving trifoliate leaves a "V" shape. Plant size may be reduced, but older leaves remain green despite S shortage. Lettuce. S deficiency results in slightly paler young leaves, while older leaves remain green. Leaves are normally formed but are thicker, stiffer, and smaller. Tomatoes. Plants tend to be smaller and lighter in color than normal plants. Yellowing may occur in various parts of the plant. Leaf shape is not affected, but leaves tend to be smaller and closer together. Petioles and stems will show a marked reddening if deficiency is severe. S-containing fluids Most fertilizer sources are sulfates and are moderately to highly water soluble. Soluble forms include bisulfites, thiosulfates and polysulfides. Solutions used to provide S to farm crops in different regions of the U.S. are: ammoniurn thiosulfate, ammonium polysulfide, ammonium bisulfate, and sulfuric acid. These sources have been produced for many years. Choice of which source is usually related to convenience of use.
Fluid Journal 1996-1998