Tuesday, 11 July 2006

Effect of Crop Rotation and Organic Amendment on Soil Nitrogen Mineralization Potential.

Mehdi Sharifi1, Bernie J. Zebarth1, David Burton2, Gregory Porter3, and Cynthia Grant4. (1) Agriculture and Agri-Food Canada, Potato Research Centre, PO Box 20280, Fredericton, NB E3B 4Z7, Canada, (2) Dept of Engineering, Nova Scotia Agric. College, Truro, NS B2N 5E3, Canada, (3) Dept of Applied Ecology and Environmental Science, Univ of Maine, Orono, ME 04469-5722, (4) Agriculture & AgriFood Canada, Brandon Research Centre, Grand Valley Road, Brandon, MB R7A5Y3, Canada

In humid environments, soil N supply is controlled primarily by soil N mineralization. Currently, there are no practical methods for predicting the magnitude of soil N mineralization. Consequently, it is difficult to consider differences in soil N mineralization which result from different crop rotations and organic amendments when making crop fertilizer N recommendations. Identification of an appropriate index of soil N mineralization can therefore provide economic benefits to producers while reducing the environmental impacts from excessive N fertilizer use. The Amino Sugar-N Test (ASNT), which simply estimates exchangeable amino sugar-N and ammonium-N, shows promise as a tool for this purpose. Samples were collected from existing long-term rotation experiments in Maine, USA on medium-textured podzolic soils to (1) evaluate the ability of the ASNT to detect differences in soil N mineralization potential resulting from compost addition and different crop rotation sequences and (2) test the possibility of using the Direct Distillation (DD) method as an alternative for the ASNT. Pre-plant soil samples were collected from 0-15 cm depth from the potato phase of a split plot experiment. Main plots were with or without an organic amendment and subplots were 3 long term rotations (1-potato-barley; 2-potato-soybean-potato-barley; 3-potato-soybean-barley-alfalfa/timothy). Preliminary results show that the ASNT and DD tests were significantly higher in rotations 1 and 2 compared with rotation 3 and higher in amended compared with non-amended treatments. The KCl extractable NO3- and NH4+ concentrations were also significantly higher in rotations 1 and 2 compared with rotation 3. These ASNT and DD methods were positively correlated (r = 0.85) and had high positive correlations with KCl-NH4 (0.51 and 0.63, respectively).The DD method had a lower coefficient of variation (CV) compared with ASNT (16% compared to 23%, respectively) which may be due in part to higher sensitivity of the ASNT to incubation temperature. Both methods are very simple and economic and do not require use of concentrated acids which makes them desirable in terms of human and environmental health. Future efforts in field validation of methods and determining the forms of soil N measured by these methods are required.

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