Influence of Long-term Tillage, Straw, and N Fertilizer Management on Crop Yield, N Uptake, and N Balance Sheet in Two Contrasting Soil Types

Field experiments (established in autumn 1979, with monoculture barley from 1980 to 1990 and barley/wheat-canola-triticale-pea rotation from 1991 to 2008) were conducted on two contrasting soil types (Gray Luvisol [Typic Haplocryalf] loam soil at Breton; Black Chernozem [Albic Agricryoll] silty clay loam soil at Ellerslie) in north-central Alberta, Canada, to determine the influence of tillage (zero tillage and conventional tillage), straw management (straw removed [S-Rem] and straw retained [S-Ret]), and N fertilizer rate (0, 50 and 100 kg N ha(-1) in S-Ret, and only 0 kg N ha(-1) in S-Rem plots) on seed yield, straw yield, total N uptake in seed + straw (1991-2008), and N balance sheet (1980-2008). The N fertilizer urea was midrow-banded under both tillage systems in the 1991 to 2008 period. There was a considerable increase in seed yield, straw yield, and total N uptake in seed + straw with increasing N rate up to 100 kg N ha(-1) under both tillage systems. On the average, conventional tillage produced greater seed yield (by 279 kg ha(-1)), straw yield (by 252 kg ha(-1)), and total N uptake in seed + straw (by 6.0 kg N ha(-1)) than zero tillage, but the differences were greater at Breton than Ellerslie. Compared to straw removal treatment, seed yield, straw yield, and total N uptake in seed + straw tended to be greater with straw retained at the zero-N rate used in the study. The amounts of applied N unaccounted for over the 1980 to 2008 period ranged from 1114 to 1846 kg N ha(-1) at Breton and 845 to 1665 kg N ha(-1) at Ellerslie, suggesting a great potential for N loss from the soil-plant system through denitrification, and N immobilization from the soil mineral N pool. In conclusion, crop yield and N uptake were lower under zero tillage than conventional, and long-term retention of straw suggests some gradual improvement in soil productivity.