Effect of straw management and nitrogen fertilizer on selected soil properties as potential soil quality indicators of an irrigated Dark Brown Chernozemic soil

Abstract

Cereals grown under irrigation in the Canadian prairies produce large amounts of residues. An experiment initiated at the Agriculture and Agri-Food Canada Research Centre, Lethbridge, Alberta, in the fall of 1986, to investigate five straw management treatments (1, chopped straw/fall tillage [straw incorporated]; 2, chopped straw/spring tillage [straw incorporated]; 3, straw baled/fall tillage; 4, straw baled/spring tillage; 5, straw baled/direct seeding) and three fertilizer N rates (0, 100, and 200 kg N ha−1) on crop yields under irrigation, was sampled in April 1995 to examine the effect of straw management and fertilizer additions on selected soil chemical characteristics as potential soil quality indicators. If yield is not used, can we evaluate soil quality from a soil genesis baseline or is it crop growth driven? Differences among straw management and fertility treatments have already supplied information on the effects of these treatments after 8 yr. The treatment in which the straw was baled and the land not tilled had the highest soil bulk density. Total soil organic C and N were highest for the straw baled/no tillage treatment and the 200 kg N ha−1 application. Total C was higher for the fall than spring tillage treatments, while total N was lower for the spring than for the fall tillage treatments when straw was incorporated. Light fraction (mg kg−1 C) was highest for the chopped straw and zero fertilizer additions. For several biologically related characteristics, e.g., mineralizable N, biomass C, biological index N, and hydrolysable N, there were significant interactions between straw management treatments and fertility levels. Monosaccharides at the zero fertility level were generally of microbial origin, while plant-origin monosaccharides were more prevalent as the fertility level increased. It is concluded that the present use does not lead to soil erosion, does not pollute groundwater, and does grow plants; with the help of outside resources, any one straw management treatment can be considered as valid in the anthropocentric sense of soil quality. Since the interpretation of significant effects of treatment on soil properties must be carefully considered depending on the crop selected, the concept of soil quality is thus open to question and debate. Key words: Soil quality, straw management, intrinsic value, tillage, labile organic matter