Selective weed suppression by cover crop residues: effects of seed mass and timing of species’sensitivity

Laboratory bioassays have shown that large-seeded species better tolerate cover crop residue–mediated stress than small-seeded species. This provides the potential for selective suppression of small-seeded weeds in large-seeded crops. We conducted two field experiments in which seedling emergence of a range of crop and weed species was monitored in soil without cover crop residues and soil with recently incorporated lucerne, winter oilseed rape or winter rye residues. A positive relationship was found between seed mass and tolerance to winter oilseed rape and lucerne residues in both experiments, whereas winter rye residues did not inhibit seedling emergence. Both the gradual reduction in residue-mediated inhibitory potential with time in the first experiment, as well as the sudden increase in lucerne residue–mediated inhibitory potential following a severe rainfall event in the second experiment, illustrated the importance of temporal dynamics. Therefore, we hypothesised that time between residue incorporation and receptor plant emergence could serve as an additional variable for explaining the variation in inhibition of seedling emergence among receptor plant species. Re-analysis of data from two previously published field experiments revealed that seed mass and time of emergence only contributed significantly to explaining variance in receptor plant emergence when both these factors were included in the analysis. Our findings suggest that considering temporal synchrony of receptor species’ sensitivity and potential residue effects in field studies provides a valuable framework for analysing crop residue-mediated effect

Comparison of alternative pest and soil management strategies for Maine potato production systems

AbstractPotato acreage and total production in Maine have declined steadily since the 1960s. In 1991, a University of Maine research team established a large-scale, long-term, comparative study of three factors that form the foundation of productive potato cropping systems: soil management, pest management, and variety choice. This study, the Potato Ecosystem Project, included 96 main plots (5.8 ha total) and near-by “component studies.” The project contrasted amended vs. unamended soil management strategies; conventional vs. reduced-input vs. bio-intensive pest management strategies; and disease and stress susceptible vs. tolerant potato varieties. Given recent concerns over resistance to pesticides and increasing costs of agricultural chemical inputs, the reduced-input and bio-intensive pest management systems provided encouraging results. Weed growth was similar in the conventional and reduced-input systems. Colorado potato beetle thresholds were exceeded less often and their densities were lower in the bio-intensive system than in the reduced-input and conventional systems. Lady beetles, which are major aphid predators, were more abundant in the bio-intensive pest management system compared with the reduced-input and conventional systems in 5 of the 6 years. Tuber yield and quality were maintained at a high level in the reduced-input system, although difficulties with plant disease, nutrient and weed management contributed to significantly lower yields in the bio-intensive pest management system. Economic analysis indicated that from 1993 to 1996, the reduced-input system had a greater return over variable cost (avg. $973 ha-1) than the conventional (avg.$890ha-1) and bio-intensive pest management systems (avg. $578ha-1). The amended soil management system achieved rapid improvements in soil quality: soil organic matter, water stable aggregates, potassium, and soluble inorganic phosphorus contents increased while requirements for synthetic fertilizers were reduced. These improvements in soil quality enhanced late-season crop vigor, canopy duration and tuber quality, and increased yields by 13% and 30% over the unamended system in 1994 and 1995, respectively, but not in 1996. Improved crop vigor in the amended soil management system also benefited weed control efforts by encouraging a more weed-suppressive potato crop. In the biointensive pest management system, in which weeds were controlled mechanically, the amended soil management system had less weed biomass than the unamended soil management system in 1994 and 1995. Conversely, the amended soil management system consistently increased flea beetle populations and, in one of two years, the incidence of Rhizoctonia. The choice of potato variety also affected pest dynamics. Total aphid density (all aphid species considered together) and almost all disease ratings were higher on ‘Superior’ than ‘Atlantic’ potato.</jats:p