CHAMBERSBURG, Pa. — Those traveling throughout Franklin County have likely seen producers hard at work; removing the first forage harvest of the year. Adequate soil fertility is critical for producing a second, third, fourth and potentially fifth harvest within the season. Consider whether or not your forage crop may need additional inputs of nitrogen, phosphorous, and potassium to maintain a productive stand. The nitrogen needs of forage crops are based on estimated crop yields in each cutting, while phosphorous and potassium needs are determined by soil test or based on estimated crop removal of nutrients in each cutting. It is recommended that producers soil test a minimum of every three years to increase the accuracy of recommendations and optimize crop production.
Forage nitrogen needs will vary based on the proportion of legumes and/or grass in the stand. Forage legumes, when properly inoculated, should not need any additional nitrogen for production. Nitrogen applications to legume stand may actually decreased the longevity of the stand and invite competition from weeds. For those managing grass stands or mixtures of grass and legume stands, stands with 50% or less legume will benefit from nitrogen applications. A general recommendation is 50 pounds of nitrogen for each ton of forage harvested over the course of a year.
One-third of this total quantity of nitrogen should be applied at green-up in the spring, and the remaining split evenly between cuttings. Splitting the nitrogen applications between cuttings is recommended because nitrogen is dynamic in the crop system and vulnerable to losses; in addition, excessive nitrogen applications may lead to nitrate toxicity issues when fed. An example: a grass forage field produces 3 tons per acre annually, it will require 150 lbs of nitrogen (equivalent to 326 pounds of urea). If the forage will be cut three times, 50 lbs of nitrogen should be applied at greenup and another 50 lbs of nitrogen applied after each subsequent cutting.
Although fall is often considered an optimal time to apply phosphorous and potassium fertilizers for forages, it is possible to make applications after the first harvest if necessary. Optimum levels of phosphorous and potassium promotes tillering, root development, and drought tolerance in our forages. The fertility rates should be determined by soil testing or through calculations of estimated crop removal. Take care in avoiding overapplications of potassium; forages may take up more potassium than is required (known as luxury consumption) leading to reduced economic returns and increasing the potential of poor animal performance.
When treating forages with manure, they are best applied in the fall or spring, ensuring there is time for the nutrients and material to be incorporated into the soil. In situations where legumes will receive manure, this application should be made in the fall, a point in the growing season when the manure can provide a useful replenishment of P and K fertility if needed, while minimizing drawbacks.
–Brittany Clark, Penn State Extension