Economic Feasibility of Using Composted Manure on Irrigated Grain Sorghum

The economic feasibility of using composted manure from western Kansas feedlots in combination with commercial N in the production of irrigated grain sorghum [Sorghum bicolor (L.) Moench] was evaluated. Effective disposal of large quantities of manure from large scale feedlots has been a concern. Yield data from a west central Kansas experiment station study was used to estimate a quadratic production function where grain sorghum yield is a function of compost and commercial N application rates. Four rates of commercial N (0, 55, 110, and 165 lb/acre) and five rates of composted feedlot manure (0, 0.9, 1.8, 3.6, and 7.2 tons dry matter per acre) in a factorial arrangement were applied to irrigated grain sorghum. The production function estimate was used to determine the combination of composted manure and commercial N, which maximized net returns. The results suggest that a compost application rate of 1.5 tons/acre with 110 lb/acre of commercial N would be economically feasible when the price of commercial N, including application charges, is $0.15/lb and the price of compost is $7.68/ton. Once the price of compost reaches $9.50/ ton compost use is no longer economically feasible. Research Question Disposal of manure is a concern for the feedlot industry. The use of composted animal manure has been suggested as a substitute for commercial N fertilizer. This study evaluates the economic feasibility of using composted manure as an N source in combination with commercial N for producing grain sorghum. Literature Summary Previous studies of composted animal manure have examined the agronomic value of composted manure as an N source rather than its economic feasibility. It has been found that increasing rates of composted manure or commercial N both increased yields, but each partially substituted for the other when combined. Study Description Yield data from a west central Kansas experiment station are used to determine the economic feasibility of compost applications using a production function. Four rates of commercial N (0, 55, 110, and 165 lb/acre) and five rates of composted feedlot manure (0, 0.9, 1.8, 3.6, and 7.2 tons dry matter per acre) were applied to irrigated grain sorghum on a Ulysses silt loam. The production function is incorporated into a net return function to determine the optimal combination of compost and commercial N application rates which maximizes net returns to the farm manager. Applied Questions What combination of compost and commercial N maximizes net returns to grain sorghum? The most economic combination of commercial N and compost was determined for a range of input costs. The results indicate that some use of compost is economically feasible but is highly dependent upon compost costs. When the price of commercial N is $0.Wlb, and the price of compost is $7.68/ton including custom application charges, the highest net return is generated by using 110 lb/acre of commercial N and 1.5 tons/acre of compost. When the price of commercial N is $0.30/lb, the amount of compost used will rise to 2.3 tons/ acre. The amount of compost used at each of these commercial N prices is indicated in Fig. . Because application charges for compost vary from a low of a $1.68/ton to a high of $5/ton, a range of compost prices—including application charges—are used to determine the optimal combination of compost and commercial N (Fig. ). When the compost price is $6/ton and commercial N is $0.15/lb, 100 lb/acre of commercial N and 3.3 tons/acre of compost maximize net returns. If the cost of compost rises to $9.50/ton, however, no compost will be used. This cost is within the range of current charges. Compost cost and use.