Nitrogen Fertilization Affects Economic Return from Crabgrass Hay

‘Red River’ crabgrass [Digitaria ciliaris (Retz) Koel.] is a warm-season annual with high yield and nutritive potential given proper management, including nitrogen. With the volatility of commercial N costs, forage producers must carefully evaluate its use. Results of a 3-year experiment that measured effects of N fertilization rates on hay tonnage and crude protein concentration (CP) were used to develop a cost:return analysis. Rates of 0, 50, 100, 150, and 200 lb N/acre were used to project an economical optimum N rate for crabgrass. The value of hay CP was estimated by balancing rations using soybean meal to supply deficiencies of crabgrass hay with different CP concentrations. Annual dry matter yield increased linearly to a plateau of 4.4 tons/acre with CP of 10.5% from 107 lb N/acre. When crabgrass CP was given its predicted replacement value of $3.25 per point at the 5-year average N price ($0.51 per lb), the optimum rate of crabgrass N fertilization was 107 lb N/acre. However, as the value of CP increased, the optimum rate of N fertilization increased to the maximum experimental level, 200 lb/acre, resulting in 13.1% CP. Actual and variable projected costs and returns can be obtained (and modified) from the available spreadsheet to evaluate alternatives.