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Fluid Journal : Fluid Journal 1993-1995
2 Fluid Journal Spring 1995 Corn (deficiency right) Soybeans (deficiency left) Wheat (deficiency left) Alfalfa (deficiency left) Clover (deficiency right) Cotton (dificiency left) Peanuts (deficiency left) Lettuce (deficiency left) Tomato (deficiency left) Figure 2. Specific symptoms of sulfur hunger in crops. Soil texture. Leaching of sulfate-S from sandy soils is more likely than from finer-textured loams and clays. Crop response to S is most common on coarse-textured soils. Organic matter. Soils containing less than two percent organic matter are most commonly S deficient. However, deficiencies do occur on soils containing higher levels. Each percent of organic matter releases about 5 lbs of S per acre per year. Water quality. Lakes and rivers usually contain higher levels of S than do deep water wells. When irrigating, analyze water sources in order to determine their S concentrations. Plant analysis and soil testing for 5, including subsoil, are also recommended on those soils suspected of being marginal or deficient. Role of S S is absorbed by plant roots as the sulfate anion. It can also enter plant leaves from the air as sulfur dioxide (SO2). In the plant it: • helps develop enzymes and vitamins • promotes nodulation for N fixation by legumes • aids in seed production • aids in protein formation • is necessary in chlorophyll formation, although it is not a constituent of chlorophyll. NS boosts yields The need for S is closely related to the amounts of N available to crop plants. This close relationship should not be surprising, since both are constituents of proteins and are associated with chlorophyll formation. Scientists have suggested that N:S ratio in plants is a good diagnostic guide for determining S deficiency. While some of the ratios used in experimentation may he open to questioning, the strong relationship between N and S is nevertheless one that cannot be ignored when N fertilizer-use efficiency is evaluated. Research in Minnesota (Figure 3) showed how best corn yields were obtained when ratios were between 5:1 and 8:1 (N:S). N and S are further linked by sulfur's role in the activation of the enzyme nitrate reductase, which is necessary for the conversion of nitrate to amino acids in plants. Low nitrate reductase activity depresses soluble protein levels, while
Fluid Journal 1996-1998