Fig. 1. Average crop yields and soil NO₃–N levels over 14 yr of conventional and no-till production at the KBS LTER site between 1989 and 2002. The crop rotation consisted of corn and soybean grown in 1:1 rotation until 1995 when the rotation was switched to corn–soybean–wheat. Corn was grown in 6 yr, soybean in 5, and wheat in 3. Asterisks indicate significant differences between tillage treatments for a particular crop (n = 6 replicate blocks). Data are adapted from annual crop yields presented in Grandy et al. (2006).