CROP RESIDUE MANAGEMENT PRACTICES, AND N AND P FERTILIZER EFFECTS ON CROP RESPONSE AND ON SOME PHYSICAL AND CHEMICAL PROPERTIES OF A BLACK CHERNOZEM OVER 25 YEARS IN A CONTINUOUS WHEAT ROTATION

Abstract

In the Black soil zone of the Canadian Prairies seedbed preparation is important for handling crop residues from high yields and for incorporating herbicides and fertilizers into soil in the fall or prior to seeding in spring. There are numerous tillage implements available to the producer for this operation. The question often arises as to the relative merits and demerits of using these implements, especially with respect to their effect on yield and on soil quality. A 25-yr (1959–1983) continuous spring wheat study was carried out at Melfort, Saskatchewan, in a split-plot design. The main plots were: four fall tillage implement treatments (plow, heavy duty cultivator, one-way disc and double disc), chopped straw in the fall and spring burn of straw. Four rates of fertilizer (0/0, 5/10, 22.5/10 and 45/10 kg ha−1 N/kg−1 ha−1 P) were subplots from 1959 to 1977; the fertilizer rates were doubled for 1978 to 1983. The results showed that there was no significant effect of tillage on yield but there was a significant fertilizer by tillage interaction. The spring burn treatment gave the highest yield (2073 kg ha−1) and the plow treatment the lowest yield (1963 kg ha−1). Fertilizer increased yields when moisture was adequate and either had no effect or depressed yields when precipitation was low. Only the plow treatment caused a loss of organic C and N. All tillage treatments increased the erosive fraction of the soil (fraction < 0.83 mm) compared to the chopped straw and spring burn treatment. The application of the 90/20 kg ha−1 rate of N and P fertilizer decreased the proportion of soil aggregates < 0.83 mm. There was no significant effect of tillage treatment on soil moisture conserved over the winter. There also was no tillage effect on NO3-N in the soil measured in the spring, but burning caused a significant increase in sodium bicarbonate-soluble P. The chopped straw treatment was concluded to be the best choice because the unincorporated residues will protect the soil best through the fall and winter and it is the easiest to implement. Where herbicides or fertilizers need to be fall-incorporated, any of the mechanical tillage implements except the plow should be equally suitable. Key words: Organic matter change, tillage, soil moisture, erodible aggregates, grain protein