Economic value of biosolids in a semiarid agroecosystem
Over half of the municipal biosolids generated in the United States are being applied to agricultural land. More information is needed on crop response to biosolids application and on the optimal level of the application from an economic prospective. With this in mind, data from two sites used in a long-term biosolids application study of an Eastern Colorado wheat (Triticum aestivum L.)–fallow rotation was analyzed using multiple regression analysis. The site on which biosolids had been applied since 1982 showed little significant (p < 0.10) response to biosolids added for the years studied. These plots also averaged one third higher in total N in the top 20 cm of soil. The other site, started in 1993, showed a very significant response to biosolids. For this site, the estimated maximum wheat yield was obtained at a biosolids application rate of 9.0 Mg ha–1. The economically optimal level of biosolids to apply depended on both the price of wheat and the cost of the biosolids. With wheat price of $0.20 kg–1 (USD) and a cost for biosolids (including application cost) of $4.00 Mg–1 the optimal level of biosolids applied was 7.3 Mg ha–1. Given an N fertilizer price of $1.10 per kg, a producer could afford to pay $7.47 Mg–1. Using biosolids as a soil amendment can have positive economic benefits; however, it needs to be monitored to avoid excessive nitrate accumulation or excessive levels of other nutrients or heavy metals.