INFLUENCE OF LONG-TERM TILLAGE, STRAW AND N FERTILIZER ON BARLEY YIELD, PLANT-N UPTAKE AND SOIL-N BALANCE

Long-term influence of N fertilizer, tillage and straw on crop product ion and soil properties are not well known in central Alberta. Field e xperiments were established in autumn 1979, on a Black Chemozemic soil and on a Gray Luvisolic soil in north-central Alberta to determine th e long-term effect of tillage, straw and N fertilizer on yield and N u ptake of barley (Hordeum vulgare L.). Fertilizer N was applied annuall y at 56 kg ha(-1). The 11 year averages of barley yields and N uptake under zero tillage were lower than under conventional tillage. Retenti on rather than removal of straw tended to reduce barley yield for the initial 6 years and 2 years at Site 1 and Site 2, respectively. A simp le mathematical model of average annual plant N uptake and grain yield could account for most of the variation in the data observed at both sites (R(2)=0.907; P <0.01). Final values of soil N, calculated using a mass balance approach, agree closely with values measured at the end of the eleventh year. Conventional tillage and zero tillage, with add ition of fertilizer N and retention of straw, were the only treatments with apparent but small net addition of N to soil at Site 1 (40 kg ha (-1) and 117 kg ha(-1), respectively). At Site 2, only the zero tillag e treatment with addition of fertilizer and retention of straw gained soil N (29 kg ha(-1)). In conclusion, soil ecosystems functioning in s ubhumid environments with slight to moderate heat limitations such as those in central Alberta can adapt, within a few years, to zero tillag e practices with full retention of straw.