Energy usage, greenhouse gases, and multi-tactical weed management in organic rotational no-till cropping systems

A farming systems model was parameterized in Chapter 1 to assess energy use and greenhouse (GHG) emissions of grain cropping systems that span a range of tillage intensity and external inputs. Despite lower yields compared to the conventional systems (20% lower), organic rotational no-till required 25% less energy and 33% less labor than standard organic management. Our findings illustrate that energy and GHG emission reductions associated with integrating legume cover crops and reducing tillage frequency are viable ways of increasing the sustainability of grain production. However, management improvements are needed for organic growers to realize benefits from reduced tillage.;One challenge is growing enough cover crop biomass (i.e. mulch) to adequately suppress weeds. In Chapter 2, we report on an experiment designed to test two approaches to increase cereal rye biomass: (1) increasing soil fertility and (2) increasing cereal rye seeding rate. Rye biomass increased with poultry litter applications (675, 768, and 787 g m-2 in the 0, 80 and 160 kg N ha-1 treatments, respectively), but this increase did not result in a decrease in weed biomass. In contrast, increasing rye seeding rate did not increase rye biomass, but did result in a reduction in weed biomass (328, 279, 225 g m-2 in the 90, 150 and 210 kg seed ha-1, treatments respectively).;Increasing cash crop density can compliment the use of cover crops for weed suppression. In Chapter 3, we report on a different experiment that evaluated cover crop mulch rate and soybean density to assess their weed suppressive ability alone and in combination. Weed biomass decreased with increasing rye mulch and weeds were completely suppressed at levels above 1,500 g m -2. Increasing soybean density alone decreased weed biomass in two of four site-years, but consistently suppressed weeds when combined with rye mulch. A quantitative framework was developed for evaluating the effectiveness of combinations of weed management practices within an annual crop in Chapter 4. This framework provides a protocol for testing for synergism between tactics and advances the quantitative underpinnings of the "many little hammers" approach to ecological weed management.