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Seasonal Trends in Selected Soil Biochemical Attributes: Effects of Crop Rotation in the Semiarid Prairie
Author: Campbell, C.A., Biederbeck, V.O., Wen, G., Zentner, R.P., Schoenau, and D. Hahn, Agriculture and Agri-Food Canada, Semiarid Prairie Agricultural Research Centre, P.O. Box 1030, Swift Current, Saskatachewan, Canada S9H 3X2
Date Created: February 26, 2002
Last Reviewed: February 01, 2007

Document Source:Canadian Journal of Soil Science. 79 (1): 73-84  (1999)
     
Summary
Soils from the 0 - 7.5 cm depth of two long-term crop rotations [continuous wheat (Cont W) and both phases of fallow wheat (F-W)] were sampled at Swift Current, Saskatchewan, Canada, from early May to mid-October, 1995 and 1996. The soil was a silt loam, orthic brown chernozemic (Kastonozem) with pH 6.0, in dilute CaC12.

Changes in organic C (OC), total N (TN), microbial biomass C (MBC) light fraction C and N (LFC and LFN), mineralizable C and N ((Cmin and Nmin), and water soluble organic S (WSOC) were assessed.

All biochemical attributes, except MBC, showed higher values for Cont W than for F-W, which reflected the historically higher crop residue inputs, less frequent tillage, and drier conditions on Cont W.

Based on the seasonal mean values for 1996, it was concluded that after 29 years, F-W had degraded solid organic C and total N by 15% compared to Cont W. In the same period it had degraded the labile attributes, except MBC. WSOC was degraded by 22%, Cmin and Nmin by 45% and LFC and LFN by 60 - 75%.

Organic C and TN were constant during the season because one year's C and N inputs were small compared to the total soil C or N.

All the labile attributes varied markedly throughout the seasons. The majority of the seasonal variability was explained by soil biochemical attributes in terms of C and N inputs from crop residues and rhizodeposition, and the influence of soil moisture, precipitation and temperature.

The biochemical attributes were related to soil moisture and the weather variables, which accounted for 20% of the variability in MBC, 27% of Nmin, 29% for LFC, 52% for Cmin, and 66% for WSOC. In all cases the biochemical attributes were negatively related to precipitation, soil moisture, temperature and their interactions.