Campbell, C. A., Lafond, G. P., VandenBygaart, A. J., Zentner, R. P., Lemke, R., May, W. E. and Holzapfel, C. B. 2011. Effect of crop rotation, fertilizer and tillage management on spring wheat grain yield and N and P content in a thin Black Chernozem: A long-term study. Can. J. Plant Sci. 91: 467-483. We analyzed the agronomic data from a 50-yr crop rotation experiment being conducted on a fine-textured, thin Black Chernozem at Indian Head, Saskatchewan in Canada. Our objective was to determine how a change from conventional-till to no-till, together with an increase in N fertilizer rates recommended by the Saskatchewan Soil Testing Laboratory has affected wheat yields and N and P balance in the systems over the past 20 yr. The treatments assessed were fertilized (N P) and unfertilized fallow-wheat (Triticum aestivum L.) (F-W), F-W-W, and continuous wheat (ContW), and unfertilized legume green manure (LGM)-W-W and F-W-W-brome (Bromus inermis Leyss.)/alfalfa (Medicago sativa L.) hay (H)-H-H. On average, N applied to wheat grown on fallow was 6kgha-1yr-1 from 1957 to 1989 and 57kgha-1yr-1 from 1990 to 2007; for wheat grown on stubble, the N rates were 21kgha-1yr-1 from 1957 to 1977 and 85kgha-1yr-1 thereafter. Crops received P at 10kgha-1yr-1. On average, fertilizer increased wheat yield of fallow-wheat by 31%; the hay system increased fallow-wheat yield by 26% compared with unfertilized fallow-wheat in F-W-W, and the LGM system increased it by 14%. Effects were greater on stubble crop than on fallow crop, with fertilizer increasing the yield of wheat grown on stubble in the monoculture system by 114%, the hay system increasing it by 83% and the LGM system increasing it by 37%. The legume-containing rotations increased yields by increasing the N supplying capacity of the soil with the hay system being more effective than the LGM because legumes occurred more frequently in the hay rotation (3 in 6 yr vs. 2 in 6 yr). The benefit of the legume-containing systems on wheat yield may have been restricted because this unfertilized system steadily depleted available soil P. Average annualized wheat production in F-W, F-W-W and ContW rotations was unaffected by cropping frequency for the unfertilized systems, but it was directly proportional to cropping frequency for the fertilized systems. Annualized wheat production for the LGM-W-W rotation was 18% greater than for unfertilized F-W-W, but 41% less than for the fertilized F-W-W. Annualized wheat production in the hay-containing rotation was 32% less than in the unfertilized F-W-W rotation because of the less frequent presence of wheat in the hay system. Greater rates of N fertilizer in the later years increased yields and grain N content; this resulted in less residual NO3-N in the soil compared with previous years with lower fertilizer N. Thus, we expect there will be less likelihood of NO3 leaching under fallow-containing systems under no-till when updated fertilizer recommendations are used compared with previous results under conventional tillage with lower rates of N applications.
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Vol. 91 • No. 3