Changes in available nitrogen over a fallow season in an undulating landscape in southwestern Saskatchewan
Spatial and temporal bioavailability of mineral N (NO3-N) over the fallow season as influenced by conventional and no-till herbicide (chemfallow) tillage systems was studied at the landscape-scale in the Brown Soil Zone, near Central Butte, Saskatchewan. Irrespective of tillage systems, average soil temperature for the 5 cm depth increased over the summer and gradually declined as the fall approached. Although the chemfallow site showed slightly lower soil temperature, no significant differences were observed either at the landscape-scale or at the landform-scale. A distinct spatial pattern of soil moisture distribution was observed among the different slope positions: shoulder < level < footslope. Gravimetric soil moisture content over the season was always higher in chemfallow compared with conventional fallow. The bioavailability of mineral N was assessed by continuous in situ burial of anion exchange membranes and soil extraction with 2M KCl solution over the fallow season. Greater soil moisture content and lack of incorporation of crop residue into the soil in the chemfallow system caused significantly higher bioavailable N compared to conventional fallow. At the landform scale, footslope positions had significantly higher NO3-N compared with level, which was in turn higher than that of shoulder positions.
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