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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Spring 1995 Soil Organic Matter Plant and Animal Residues Atmospheric Sulfur Elemental Sulfur (S) Fertilizer Sulphate-Sulfur Fertilizer Sulphate Sulfur Plant Uptake Leaching Loss Crop Removal Bacterial Assimilation Immobilization H2S S Bacterial Assimilation Bacterial Oxidation Thus far in this series on effective management we've covered the roles N, P, K, and Zn play in crop production. In this fifth of the series we will be discussing what traditionally has been referred to as a secondary nutrient but more and more is being called a primary nutrient: sulfur. Sulfur (S) is one of nature's super nutrients and one of the oldest elements known to man. It is the thirteenth most abundant element in the earth's crust. S is essential for the production of three amino acids found in both plants and animals. These amino acids are the building blocks in the synthesis of proteins. Without proteins, plants and animals simply could not exist. Proteins provide the sustenance humans require in their diets in order to survive. Because S is used to produce amino acids, it is a part of the makeup of every living organism. Elemental S is a natural, non-toxic element. It is used in the manufacture of many health products such as sulphadrugs and ointments for skin diseases. It is also used in petroleum refining, production of fertilizers, and preservation of fruits and vegetables. S in soil Inorganic soil S (that form available to plants) occurs as the sulfate anion (SO3-). Because of its negative charge, the sulfate anion is not attracted to soil clay and organic matter surfaces, except under certain conditions. It remains in the soil solution and moves with soil water, so it is readily leached. Certain soils accumulate the sulfate anion in the subsoil, which would be available to deep-rooted crops. In arid regions, sulfates of Ca, Mg, K, and Na are the predominant inorganic S forms. Much of the soil S in humid regions is associated with organic matter. Biological transformations. similar to FFF Review Effective Sulfur Management A secondary nutrient many agriculturists now think of as primary is part of the makeup of every living organism. those of N, produce plant-available sulfate and sulfate compounds. The sulfur cycle (Figure 1) shows the relationship among atmospheric, fertilizer, and soil sources of S. Proper management ensures S uptake efficiency with minimal leaching or erosion. As shown in the figure, there is no net gain or loss of S in nature. S-deficient soils The number of S-deficient soils is increasing. Contributing factors include: • bigger crop yields removing larger amounts of S • increased use of high-analysis fertilizers containing little or no incidental S Figure 1. The sulfur cycle. • decreased use of high-S fuels and improved S removal techniques from stack gases • less use of S-containing pesticides • increased conservation tillage that immobilizes S in accumulated organic matter. Remedial action To minimize S deficiency problems in soils, scrupulous accounting for the following should help in any well planned fertility program: Crop selection. High-yielding forage crops, such as hybrid bermudas and alfalfa, remove more S and generally respond to S additions more frequently than most grain crops.
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