1Agriculture and Agri-Food Canada, Lacombe, Alberta, Canada T4L 1W1; 2Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada T6G 2E3; 3Alberta Agriculture, Food and Rural Development, Edmonton, Alberta, Canada T6H 4P2; and 4Western Co-operative Fertilizers Limited, Box 2500, Calgary, Alberta, Canada T2P 2N1
Our objective was to summarize research information from four long-term field experiments (two on grassland and two on cultivated land ) on some agronomic practices that can be used to sequester more C in the soil by following strategies of preventing loss of C from soil and/or increasing input of C to soil. In the two grassland experiments, forage grass was harvested for hay each year. The first experiment received ammonium nitrate at 0 to 336 kg N/ha for 27 years (from 1968 to 1994); concentration of total C(TOC) in the 0-5 cm soil layer increased markedly with N application (from 47.9 g/kg in the zero-N treatment to 60.2 g/kg with a rate of 56 kg N/ha), but increases were smaller in deeper layers. In the second experiment (for 11 years), where soil was deficient in N and S, applications of both N and S fertilizers were required to store more C in soil. The other two experiments were conducted on cultivated land and showed marked increase in C storage from fertilizer N as did the two grassland experiments. In the first experiment, after 11 years, zero tillage stored 4.2 Mg/ha more C in the 0-15 cm layer than conventional tillage, with annual application of 56 kg N/ha and returning to straw to soil. In the second experiment, lasting for 12 years, TOC storage in soil was increased by 7.1 Mg/ha with annual application of 75 kg N/ha. These results indicate that C sequestration in soil can be increased in the grasslands and cultivated lands using soil and crop management practices which prevent the loss of C from soil (i.e., elimination of tillage) and/or increase the input of C to soil (i.e. returning of crop residues to soil and application of required fertilizer nutrients).