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

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 saliva L.) hay (H)-H-H. On average, N applied to wheat grown on fallow was 6 kg ha(-1) yr(-1) from 1957 to 1989 and 57 kg ha(-1) yr(-1) from 1990 to 2007; for wheat grown on stubble, the N rates were 21 kg ha(-1) yr(-1) from 1957 to 1977 and 85 kg ha(-1) yr(-1) thereafter. Crops received P at 10 kg ha(-1) yr(-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 NO(3)-N in the soil compared with previous years with lower fertilizer N. Thus, we expect there will be less likelihood of NO(3) 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.