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Fig. 6. Comparisons of the post-harvest residual soil NO3–N (RSN) content for different sample classes via the box-and-whiskers diagram. The upper and lower limits of each box signify the 25th and 75th percentiles for the RSN, the horizontal line in the center of the box indicates the median, the "+" sign in each box indicates the mean, and the "whiskers" or arms represent the full range of the RSN observed in each class. The 
EONR is the difference between the total N applied and economically optimal N rate (EONR). Different letters above the upper limits of each box indicate mean significance differences at the 0.05 probability level. The sample size of each class is given below the lower limits of each box. The class with EONR = 0 contains one value from each field, which was estimated from the plateau-linear function shown in Fig. 5. All other classes consist of observations classed from individual plot samples.
