How Much Does Considering the Cost of Lime Affect the Recommended Level of Nitrogen?

Abstract

Ammonium‐based N fertilizers acidify soils. Lime used to correct soil pH is a substantial cost to producers. Recommendations about the optimal levels of N to apply typically ignore the cost of the lime needed due to N fertilization acidification. This study aimed to determine the effect of considering the cost of lime on recommendations about the optimal level of N. Yield response and soil pH change functions were estimated and used to determine the optimal levels of N and lime. The study also developed a new version of a linear response plateau function that allows the yield plateau to vary by year with respect to N but not soil pH. The stochastic linear response plateau fit the data best. At current input and output prices, considering the cost of lime reduced the optimal level of N by as much as 11.3%, from 168 to 149 kg ha−1 yr−1 The acidification potential due to N fertilizer increased nonlinearly as the N rate increased. Nitrogen acidification appears to be more severe with N application rates above the consumptive potential of the crop than with N that is used by the plant. The timing of N application had no significant effect on forage yield, but splitting N into fall and spring applications significantly reduced acidification due to excess N fertilization. Recommendations of how much N to apply were 149 kg ha−1 yr−1 with a pH of at least 5.88.