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Summary

Withholding K fertilization reduced the available soil K to low levels in less than two years. This minimized K uptake and resulted in very low forage K concentrations. With 100 lbs actual N fertilizer per acre applied at spring greenup and after spring harvest in June, forage K content averaged 1.1% in June forage and 0.6% in September forage. Although reed canarygrass in these studies did exhibit K deficiency symptoms, stands have survived and have been productive with adequate N fertilization. We recommend K fertilization in the form of 60-100 lbs K20 per acre as commercial fertilizer or manure if first cut forage < 1.7% K, or stand persistence will be at risk. Forage analysis for K should be done using wet chemistry not NIRS.

Forage quality of grass in a two harvest system will not be of sufficient quality for lactating cows, but is sufficient for dry cows. The fiber content of grass harvested in mid to late June in New York State will be 65-70% NDF. Fiber content of regrowth grass harvested in mid to late September will be in the 50-60% NDF range. If 75-100 lbs actual N/acre are applied to each cutting, CP content of forage should be between 12-15% for both harvests. In vitro true digestibility will be around 60% for both harvests.