A 2-year study compared milk production and profitability for confinement feeding versus rotational grazing. Guernsey and Guernsey x Holstein cows grazed perennial grass pastures from mid-May to October or were fed in confinement. Averaged over both years, confined cows produced 7% more milk; their milk was similar in fat concentration to that of grazing cows. Body weight changes and health of the two groups were similar. Net return per cow averaged $64 higher for rotational grazing than for confinement because of lower costs for feeding, facilities, equipment, and labor. Intensive rotational grazing of pastures is a competitive alternative for dairy cow feeding. However, farmers in the northern U.S. will still require stored feeds from late fall through early spring.

We conducted a field experiment within a low-input reduced tillage trial to determine how a cover crop affects inoculum levels of vesicular-arbuscular mycorrhizal (VAM) fungi. Plots with and without the hairy vetch cover crop were established on September 30, 1993, under moldboard plow (MP), chisel-disk (CD), and no-till (NT) treatments in low-input (LI) management, and MP in conventional (CONV) management. We conducted a 3-week colonization assay in the greenhouse with bahiagrass seedlings to assess the relative colonization potential of the soils in the fall and following spring. Hairy vetch roots were colonized by indigenous VAM fungi by 65 days after planting, with plants from NT being more colonized than plants from MP or CD plots. Spore populations were greater in the LI than in the CONV system. The beneficial effect of the cover crop on VAM spore populations in soil was manifested in the spring, with the Glomus type group more abundant in plots with cover than without it. The greenhouse bioassay showed that colonization potential of spring 1994 soil samples was higher in plots with cover than without cover for both the LI and CONV systems. Just one season of an overwintering cover crop of hairy vetch increased the inoculum of VAM fungi the following spring before the next cash crop was planted.

Residues of dead cover crops can suppress weeds by providing a mulch on the soil surface. The cover crop usually is killed with herbicides, but a mechanical method is desirable in systems intended to reduce chemical use. We designed and built an undercutter to kill cover crops by severing their roots while flattening the intact aboveground biomass on the surface of raised beds. We studied which cover crop species could be killed with the undercutter and compared the weed control potential of cover crop residues after flail mowing, sicklebar mowing, and undercutting.

Whether a species was killed by the undercutter depended primarily on growth stage. Species that were in mid- to late bloom or beyond, including rye, hairy vetch, bigflower vetch, crimson clover, barley, and subterranean clover, were easily killed by undercutting. There were no differences in dry weights of broadleaf weeds between the undercut and simulated sicklebar mowed treatments, both of which had less weed biomass than the clean-tilled or flail-mowed plots.

Livestock production and manure handling decisions often have been treated in the literature as separate enterprises. Policymakers, too, have ignored the interactive nature of manure management by focusing on land application for nutrient disposal. This study outlines a systems approach to describe the interrelated decisions producers face, using examples from North Carolina and Iowa that show how producers' attitudes toward manure management lead them to handle manure differently in different regions. In North Carolina, nutrients in manure are “not wanted.” There are economic incentives to treat manure, thus reducing its nutrient content, and to apply it on as little land as possible. In Iowa, nutrients are “not wasted.” Producers conserve the nutrients in manure and use them more fully, applying manure to higher value crops such as corn. Policies that influence manure management can be made more effective by accounting for the differences in producers' incentives to waste or want the nutrients.

We used linear programming to simulate adoption of manure disposal technologies in eastern Colorado. Manure, either raw or composted, is assumed to be applied to irrigated cropland within 20 miles of feedlots in five subregions of eastern Colorado. We constrained the application so that total N application is no more than the amount used by the crop. N, P and K contents are taken into account, but no benefits are assigned to organic matter or trace minerals and no costs are assigned to soil compaction, weed seed propagation, or inconvenience. Irrigated land within 10 miles of feedlots can easily absorb all manure generated under this scenario. Manure is found to be an economical substitute for chemical fertilizers, assuming N content to be at least 50% that of fresh manure. Composted manure is either more or less profitable than raw manure, depending on its N content. Hauling costs are lower for compost, but composting costs are between $1 and $2 per finished ton. The model does not allow for mixed application of compost and chemical fertilizers, which would increase the value of compost significantly. A feedlot waste sector that composted all feedlot manure in eastern Colorado is predicted to create between 80 and 200 additional jobs.

An areawide program for biological control of the alfalfa weevil showed expected economic benefits of $2.2 billion, expressed in present value terms. Alfalfa producers and consumers of livestock products are the main beneficiaries. The control program was highly successful, with a benefit/cost ratio of about 91. Not all areawide biological pest control programs will be as successful; a benefit-cost analysis like the one described here should be performed before areawide control is initiated to identify programs expected to provide economic benefits.

Multidisciplinary approaches are being attempted by agricultural research units along with their traditional single discipline approaches. Although single discipline research will still be needed, multidisciplinary approaches present special advantages.

The potential value of multidisciplinary approaches to sustainable agriculture research will be viewed differently by researchers with different perspectives. The participants in this symposium, all of whom were experienced sustainable agriculture researchers, identified five areas as keys for success. First, to capitalize fully on the opportunities it provides, there must be a justification for using a multidisciplinary approach for the specific research topic; while some projects work best with a multidisciplinary approach, others are best done within a single discipline. Second, everyone involved, including administrators, must invest time and money to establish communication between the disciplines. Third, careful attention must be given to forming and operating multidisciplinary teams effectively so that they generate shared benefits. Fourth, new sources of research funds will become available as agencies adopt multidisciplinary approaches, and revised systems will be required to administer those funds at the university or research unit level. Finally, major adjustments in the present systems for promotion, tenure and publication are necessary to properly measure and distribute credit.

The red sunflower seed weevil, Smicronyx fulvus LeConte, is a major pest of sunflower in North and South Dakota and Minnesota. Typically, insecticides are used to reduce oviposition and prevent economically damaging larval populations from developing. In a test of a reduced-pesticide alternative, we planted early maturing sunflower in the margins around commercial fields of oilseed sunflower. The margins flowered earlier than the field interiors and acted as a trap for the red sunflower seed weevil. They were treated with an insecticide while the trap rows were blooming and before the field interior began to flower. Conventional fields entirely treated with insecticide served as checks. We compared the trap and check fields with regard to yield, the fraction of larval-damaged seeds, and economic costs (insect damage and the cost of insecticide materials and application). Yield and larval damage of seeds were comparable between check and trap fields. However, the economic costs of weevil control in the check fields was greater than in the trap fields. Trap cropping is a recommended strategy for the red sunflower seed weevil, especially where economically damaging populations of the weevil are expected.