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SOIL & WATER MANAGEMENT & CONSERVATION

Response of Potentially Mineralizable Soil Nitrogen and Indices of Nitrogen Availability to Tillage System

^a Agriculture and Agri-Food Canada, Potato Research Centre, PO Box 20280, Fredericton, NB, Canada E3B 4Z7
^b Dep. of Environmental Science, Nova Scotia Agricultural College, PO Box 550, 21 Cox Rd., Truro, NS, Canada B2N 5E3
^c Agriculture and Agri-Food Canada, Brandon Research Centre, Grand Valley Rd., Brandon, MB, Canada R7A 5Y3
^d Agriculture and Agri-Food Canada, Pacific Agri-Food Research Centre, PO Box 1000, Agassiz, BC, Canada V0M 1A0
^e Agriculture and Agri-Food Canada, Greenhouse and Processing Crop Res. Centre, Harrow, ON, Canada N0R 1G0
^f Agriculture and Agri-Food Canada, Semi-Arid Prairie Agricultural Research Centre, PO Box 1030, Swift Current, SK, Canada S9H 3X2
^g Agriculture and Agri-Food Canada, Soil and Crop Research Dev. Centre, Sainte-Foy, QC, Canada G1V 2J3

^* Corresponding author (ZebarthB{at}agr.gc.ca).

Tillage practices may affect the active fraction of soil organic N. As part of a national project to examine soil management and environmental controls on the active fraction of organic N, this study examined the effects of no-till (NT) and conventional tillage (CT) systems on the quantity of potentially mineralizable soil N (N₀) and mineralizable N pools, and the potential to detect changes in these pools using N availability indices. Preplant soil samples from the top 15 cm were collected from four long-term tillage experiments at Swift Current, SK; Woodslee, ON; L'Acadie, QC; and Agassiz, BC. Potentially mineralizable N was determined by aerobic incubation at 25°C and periodic leaching for 24 wk. The N₀ was greater under NT than under CT, but only at Swift Current. The labile and intermediate mineralizable N pools were significantly higher under NT than under CT at three of the four sites. The stable mineralizable N pool and the mineralization rate coefficient (k) were greater under NT than under CT at only one of the four sites. Adoption of NT influenced the quality of the active organic N fraction at three sites, as indicated by an increased proportion of mineralizable N in the more labile N pools. Among tested indices of N availability, KCl-extractable NH₄–N, NaOH-extractable N, Illinois Soil N Test, phosphate-borate buffer extractable N, and particulate organic C were most sensitive to tillage-induced changes in the active organic N fraction. Tillage-induced changes in the size and quality of the active organic N fraction may influence soil N supply and should be considered in optimizing fertilizer N management.

Abbreviations: N₀, potentially mineralizable nitrogen • NaHCO₃–205, ultraviolet absorbance of sodium bicarbonate extract at 205 nm • NaHCO₃–260, ultraviolet absorbance of sodium bicarbonate extract at 260 nm • CT, conventional tillage • ISNT, Illinois Soil Nitrogen Test for amino sugar nitrogen • MBC, microbial biomass carbon • NT, no-till • POM-C, particulate organic carbon • POM-N, particulate organic nitrogen • SOC, soil organic carbon • SON, soil organic nitrogen