Long-term tillage effects on cool-season soybean in rotation with barley, soil properties and carbon and nitrogen storage for fine sandy loams in the humid climate of Atlantic Canada

Conservation tillage systems may allow economical crop establishment in areas constrained by low crop heat units, but such methods need to be adapted to soil tillage requirement and crop establishment needs. Two tillage studies were conducted on fine sandy loams (Podzols) with cool-season soybean (Glycine max L. Merr.) in rotation with barley (Hordeum vulgare L.) under the cool, humid climate, and relatively short growing season of Prince Edward Island, Atlantic Canada. The objective was to evaluate the long-term productivity and protein content of soybean, developed for cool climates, under a range of conservation tillage options and to assess changes in soil properties, and soil C and N storage. The experimental design was a split-plot with four replicates. The first tillage experiment (Experiment 1, initiated in 1985) evaluated direct-drilling (DD), shallow tillage and conventional mouldboard ploughing (MP) over a 9-year-period (1989-2000). The second tillage experiment (Experiment 2, initiated in 1985), conducted over a over a 3-year-period (1991-1993), evaluated mouldboard ploughing and chisel ploughing, both conducted in the spring and fall. Although some annual variations occurred, mean crop yield and grain protein were similar among tillage treatments. Barley yield ranged from 2.5 to 3.8 Mg ha−1, while soybean yield ranged from 1.5 to 2.1 Mg ha−1. Periodic differences in grain nutrient content (P and K content) were evident but not related to any one tillage treatment for soybean or barley. In Experiment 1, the physical condition at the soil surface improved with time under direct-drilling, compared to mouldboard ploughing. Both organic C, microbial biomass C, and Mehlich III available P increased at the soil surface under direct-drilling compared to ploughing. The latter presented an environmental concern as the build-up (>200 μg P kg−1) was above plant requirement levels. Soil C and N storage in the soil profile (0-60 cm depth) did not differ between tillage systems, although total N showed a relative increase at the 0-20 cm depth under direct-drilling. Overall, conservation tillage appears a feasible strategy for the production of cool-season soybean on sandy loam soils in Atlantic Canada.