Influence of conservation tillage and glyphosate on soil structure and organic carbon fractions through the cycle of a 3-year potato rotation in Atlantic Canada

Conservation tillage (CT) practices are promising management options for potato (Solanum tuberosum L.) production in Atlantic Canada, however, concerns are expressed about the effects of glyphosate [N-(phosphonomethyl) glycine] and tillage interactions on soil organic matter and structure. The objective of this study was to compare the effects of a range (from conventional to CT) of tillage practices (with and without glyphosate) on several soil properties over each phase of a 3-year potato rotation [red clover (Trifolium pretense L.)-potato-barley (Hordeum vulgare L.)], at three sites, over a 5-year period. Four tillage practices were evaluated: (1) autumn mouldboard ploughing followed by spring secondary tillage (conventional tillage treatment); (2) spring mouldboard ploughing followed by secondary tillage; (3) autumn chisel ploughing followed by spring secondary tillage; and (4) spring CT. The temporal variation, influence of tillage, and effect of glyphosate were determined on several soil indicators (phosphatase, microbial biomass C, carbohydrates, organic C, total N, particulate C and N, bulk density and soil structural stability using both dry and wet sieving) at five stages in the 3-year rotation cycle: (1) in red clover phase, after glyphosate application but before autumn tillage; (2) in potato phase, at pre-spring tillage; (3) in potato phase, at pre-ridge tillage; (4) in potato phase, at post-harvest; and (5) in barley phase, at post-harvest. Except for soil bulk density and organic C, there were few clear temporal variations in soil properties. Tillage-induced changes, mainly related to soil loosening depth and inversion, were evident for most of the soil properties at the pre-spring tillage and pre-ridge tillage stages. Periodic and irregular influences of glyphosate were recorded on soil properties at various growth stages. However, these influences were ecologically negligible and related to loss of red clover biomass forfeited by early application of glyphosate in the autumn, rather than a direct effect of the herbicide. There were no glyphosate and tillage interactions. Overall, use of glyphosate in CT and other tillage systems on sandy loam soils had no detrimental effect on soil biological properties and associated processes such as soil aggregation. Crown Copyright © 2006.