Moving from Uniform to Variable Fertilizer Rates on Iowa Corn: Effects on Rates and Returns

This paper estimates the potential value of switching from applying nitrogen fertilizer according to SRT to applying it according to VRT in 12 Iowa counties. Change in yields, nitrogen use, and profits are estimated for individual fields and entire countries as farmers move from SRT to VRT. The county-level results indicate modest increases in returns over fertilizer costs, ranging form $7.43 per acre to $1.49 per acre. The county-level VRT production benefits are increases in yields ranging form 0.05 to 0.50 bushels per acre and reduction in production costs ranging from $1.19 to $6.83 per acre. The VRT environmental benefit for the entire study area is quite large, ranging from 77 to 172 tons of nitrogen. Increases in the price of corn and nitrogen cause the value of VRT to increase. Greater field variability from either the soil types within a field or from the best manner to treat the soil types also cause the value of VRT to increase.