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Topics : Soil Fertility for Forage Crops : Maintenance

Maintenance

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Sulfur and Forages

Sulfur deficiency is not a common problem in Pennsylvania. Conditions where sulfur deficiency might occur include: low organic matter soils, coarse textured soils such as sandy soils, areas of high rainfall, and fields that do not have a history of manure application. Acid rain is a major contributor of sulfur in Pennsylvania. Current soil tests for sulfur are not very reliable. The best approach to diagnosing a sulfur problem is to use plant tissue analysis, taking care to get a proper sample at the appropriate stage of growth. For alfalfa, as an example, the top one-third of the plant should be sampled between bud and one- tenth bloom stage. If sulfur is sufficient, the sulfur analysis of this alfalfa sample should be between 0.25 and 0.50 percent (Table 5). The ratio of nitrogen to sulfur in plant tissue is a good indicator of whether sulfur is adequate or deficient. For example, a nitrogen to sulfur ratio greater than 11 to 1 is an indication of sulfur deficiency in alfalfa.

Elemental sulfur, gypsum, and sul-po-mag are commonly used materials used to correct a sulfur deficiency. Ammonium sulfate, which is 24 percent sulfur, can be used as the nitrogen source on grasses. Grass crops require around 8 to 12 pounds of sulfur per acre and legume crops 20 to 25 pounds of sulfur per acre. These requirements can be used as guides in determining the application rate when a sulfur deficiency is suspected.