Improving organic C and N fractions in a sulfur-deficient soil with S fertilization

A field experiment was conducted over 9 years (1999 to 2007 growing seasons) in northeastern Saskatchewan on a S-deficient Gray Luvisol (Typic Haplocryalf) soil. The objective was to determine the relative effectiveness of N alone versus combined annual application of N (120 kg N ha(-1)) and S (15 kg S ha(-1)) fertilizers to a wheat-canola rotation on storage of total organic C (TOC) and N (TON) and on the light fraction organic C (LFOC) and N (LFON) in soil. Compared to N alone, annual applications of S fertilizer in spring in a combination with N resulted in an increase in soil of TOC (by 2.18 Mg C ha(-1)), TON (by 0.138 Mg N ha(-1)), LFOC (by 1,018 kg C ha(-1)), and LFON (by 42 kg N ha(-1)). The relative increases in organic C or N due to S fertilizer application were much higher for the light organic fractions (36.9% for LFOC and 27.5% for LFON) than for the total organic fractions (9.2% for TOC and 7.3% for TON). The findings demonstrate the importance of a balanced/combined application of N and S fertilizers to crops in storing more organic C and N in this S-deficient soil.