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Nitrogen Fertilization

Nitrogen fertilization greatly increases uptake of K, if there is sufficient K available for uptake. We have almost doubled the K content of grass through high N fertilization rates, compared to no fertilizer N applied. Recommended N applications are 75-100 lbs actual N/acre at spring greenup and 75-100 lbs actual N/acre after spring harvest. Once excessive available soil K is removed however, the opposite trend in forage K content emerges. High N fertilization produces high yields, but very low soil K availability results in very low forage K concentrations. It may take only one season of moderate to high N fertilization to remove excess soil K. The forage produced the first season will likely be high in K content, but may be very low in K content in all succeeding years. After two years, soil test K dropped from “Medium” to “Very Low” (32 lb K/acre) in high N/no K stands on a soil type with average K-supplying power.