!CONTRAST LinN Nitrogen {3 1 -1 -3}/10defines model term LinN as a contrast based on the 4 (implied by the length of the list) levels of existing factor Nitrogen. The user should check that the levels of the factor are in the order assumed by contrast (check the .ass, .sln or .tab files). Missing values in the factor become missing values in the contrast. Zero values in the factor (no level assigned) become zeros in the contrast.