Tuesday, November 14, 2006 - 2:00 PM
192-5
Seasonal Changes in Soil N as Affected by Soil Managements in Canadian Prairie.
Seasonal changes in soil N were studied on cropped and bare soils under two tillage systems in five sites on the Canadian prairies. Soil NH4-N concentration was not significantly affected during growing season in either cropped bare soil or cropped treatments. Its fluctuation was generally within 15 kg ha-1 at the 0-60 cm depth and was correlated with soil temperature. Unlike NH4-N, NO3-N dynamics were strongly influenced by soil management. No significant changes were observed in the bare soil, but crop uptake resulted in a sharp decline in the NO3-N concentration, particularly in the 0-15 cm profile. The total NO3-N accumulation in the 0-60 cm depth decreased as much as 10-fold from seeding to harvesting, depending on soil background NO3-N level and crop requirements. Both NH4- and NO3-N concentrations in the upper soil horizon increased after harvest due to mineralization of soil organic matter and crop residue. The elevated amount of NO3-N in soil increased the risks of N losses due to denitrification. This may occur between crop harvest and crop uptake in the following season, particularly during the early spring when soils are wet because of melting snow.
Nitrogen application increased crop biomass production. As a result of the higher biomass input, soil organic matter turn-over and nitrification were accelerated, especially in those soils with lower carbon content. Tillage system also influenced soil N dynamics, but changes were not always consistent because tillage systems modified both crop demand for N and N cycling in the soil.
Recorded presentation