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Topics : Soil Fertility for Forage Crops : Maintenance


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Manure Nitrogen on Grasses

Grasses are especially well suited to manure application because they have a high demand for all of the major nutrients in manure. Some of the precautions for manure use, discussed earlier for legumes, are also relevant for the grasses. Care must be taken to minimize damage to the grass. Damage can include smothering by spreading too heavily or unevenly, burns to new growth caused by waiting until regrowth has started before applying the manure, simple physical damage to the plants, and soil compaction from manure spreading equipment. Rates of manure application to grasses should be based on the annual nitrogen requirements of the grass and on balancing the phosphorus and potassium needs of the entire crop rotation. The rate must also be low enough so that the stand is not physically damaged by the application. When calculating the manure application rate based on nitrogen, the nitrogen availability of the manure must be considered. The amount of available nitrogen will depend on the type of manure and how long it will be exposed on the surface before it receives 1/2 inch of rainfall (Table 3).

For example, if your dairy manure has an analysis of 11 pounds of nitrogen per ton and you expect 1/2 inch of rain within four days of application, the available nitrogen would be 3.85 pounds of nitrogen per ton of manure (11 x 0.35 = 3.85 lb/ton). Thus, to supply the requirement for 1 ton of grass hay (40 pounds of nitrogen) you would need to apply a little over 10 tons of manure per acre (40 ÷ 3.85= 10.4 tons/acre). More information on manure use and calculations is provided in ST-10 "Use of Manure" sent out with all soil tests run by the Penn State Soil Testing Laboratory.