Long-Term Tillage, Straw Management, and Nitrogen Fertilization Effects on Organic Matter and Mineralizable Carbon and Nitrogen in a Black Chernozem Soil

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Abstract
Soil, crop, and fertilizer management practices may affect quality of organic carbon (C) and nitrogen (N) in soil. A long-term field experiment (growing barley, wheat, or canola)was conducted on a Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, to determine the influence of 19 years (1980 to 1998) of tillage [zero tillage (ZT) and conventional tillage (CT)], straw management [straw removed (SRem) and straw retained (SRet)], and N fertilizer rate (0, 50, and 100 kg N ha−1 in SRet and 0 kg N ha−1 in SRem plots) on macro-organic matter C (MOM-C) and N (MOM-N), microbial biomass C (MB-C), and mineralizable C (Cmin) and N (Nmin) in the 0- to 7.5-cm and 7.5- to 15-cm soil layers. Treatments with N fertilizer and SRet generally had a greater mass of MOM-C (by 201 kg C ha−1 with 100 kg N ha−1 rate and by 254 kg C ha−1 with SRet), MOM-N (by 12.4 kg N ha−1 with 100 kg N ha−1 rate and by 8.0 kg N ha−1 with SRet), Cmin(by 146 kg C ha−1 with 100 kg N ha−1 rate and by 44 kg C ha−1 with SRet), and Nmin(by 7.9 kg N ha−1 with 100 kg N ha−1 rate and by 9.0 kg N ha−1 with SRet)in soil than the corresponding zero-N and SRem treatments. Tillage, straw, and N fertilizer had no consistent effect on MB-C in soil. Correlations between these dynamic soil organic C or N fractions were strong and significant in most cases, except for MB-C, which had no significant correlation with MOM-C and MOM-N. Linear regressions between crop residue C input and mass of MOM-C, MOM-N, Cmin, and Nmin in soil were significant, but it was not significant for MB-C. The effects of management practices on dynamic soil organic C and N fractions were more pronounced in the 0- to 7.5-cm surface soil layer than in the 7.5- to 15-cm subsoil layer. In conclusion, the findings suggest that application of N fertilizer and retention of straw would improve soil quality by increasing macro-organic matter and N-supplying power of soil.

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