N does bad things when S is missing

At front left is canola with N fertilizer but no S in S deficient soil. It looks worse than canola with no fertilizer at the right. Back left is canola that received both N and S at appropriate levels. Source: Jeff Schoenau

When fields are sulphur deficient, canola that receives only nitrogen fertilizer can yield less than canola that receives no fertilizer at all. Canola plants need sulphur to produce three key amino acids: methionine, cysteine and cystine. Without the S to build these amino acids, N creates toxic amides in the plant that greatly inhibit seed set.