Protect Natural Resources, Page 2
|Pulse crops like peas can "fix" nitrogen for a subsequent crop. Crop diversity also can lower input costs such as herbicides and pesticides. |
– Photo by Eric Nielsen
Diverse, pest-resilient fields contain rich supplies of above- and below-ground beneficial organisms. Such organisms can:
antagonize insects and nematodes
inhibit growth of disease organisms
boost crops’ natural defenses
suppress some weeds by exposing weed seeds to more predators and decomposers
release nitrogen more slowly, giving larger-seeded crops a head start in spring
Crop diversity can lower input costs, studies show. In an Ohio State University study, average per-acre costs for herbicides and insecticides were only $20 for a corn-soybean-wheat-hairy vetch rotation, compared with $36 for a typical corn-soybean system. In Alabama, scientists found that two years of switchgrass provided equivalent root knot nematode control as continuous peanuts with nematicide. In Maryland, two years of a sorghum-sudangrass summer crop, combined with poultry litter, effectively stemmed root knot nematodes in potatoes.
For more information on the many benefits of diversification to pest management, see SAN’s ‘Naturalize’ Your Farming System: A Whole-Farm Approach to Managing Pests.
Reduced Water Use
In the nation’s drier regions, many farmers use rotational strategies to conserve soil moisture or harvest a crop despite drought. Many, in fact, frequently fallow their land – leaving it idle to accumulate moisture for the following crop. In 1997, 22 percent of the nation’s wheat was grown in wheat-fallow rotations. Fallow periods, however, expose soil to wind and water erosion and organic matter loss. Moreover, a more diverse rotation can improve yields.
A long-term study at the University of Wyoming found that partially replacing fallow with Austrian winter peas improved water use efficiency, added nitrogen to the subsequent wheat crop and provided a nutritious forage for lambs. Researchers direct-seeded peas into wheat stubble in late summer. In late spring, they turned lambs out to graze the peas for three weeks, resulting in better gain – and profits. Planting peas every fourth year increased net return per acre from $7 to $13, averaged over the four years. Moreover, while summer fallow generally only saves 20 to 40 percent of precipitation, the peas used rain or snow otherwise lost to runoff and soil evaporation.
University of Wyoming researcher Jim Krall praises the potential for the winter-hardy medic Medicago rigidula. In winter annual pastures alternating with wheat, M. rigidula reseeds itself reliably in fall and has produced more than 3,700 pounds of dry matter per acre by mid-May.
Proso millet needs the least amount of water of any cereal. Shallow rooted, it doesn’t tolerate drought as much as it evades it by maturing in 60 to 90 days after planting. Its low straw-to-grain ratio also contributes to its water-use efficiency. In moisture-limited areas of the central Great Plains, winter wheat-proso-fallow rotations provide an extra cash crop every three years. The alternative oilseeds sunflower, canola and crambe – one of the richest known sources of erucic acid, used in industrial lubricants – are all feasible in dryland rotations with winter wheat in that region.
In northern Idaho, condiment mustard’s 4-foot effective rooting depth extracts more soil moisture than peas or lentils, which is helpful in low-rainfall years. All three rotation crops are very good at breaking up disease, insect and weed cycles in cereal crops, but mustard’s more plentiful residue does a better job of protecting erosion-prone winter soils: studies show it maintains greater than 50 percent surface cover, compared with 30 percent for pea and 25 percent for lentil.
Encouraging prices have prompted “steady adoption” of condiment mustard by the region’s farmers, said University of Idaho extension specialist Stephen Guy.
In diversified systems that border sensitive waterways, riparian buffers strips comprised of trees, shrubs and grasses intercept sediment, nutrient and pesticide runoff. Forested riparian buffers help to reduce stream bank erosion, protect water quality, enhance aquatic environments and provide wildlife habitat.
According to USDA’s Natural Resources Conservation Service (NRCS), buffer strips can remove up to 50 percent of nutrients and pesticides, up to 60 percent of certain pathogens and up to 75 percent of sediment that might otherwise leave a field.
“In some cases, installing buffers helps producers comply with environmental laws and regulations,” said Steve Carmichael, NRCS state resource conservationist in Louisiana. “It offers an effective way a producer can demonstrate concern for the environment and a commitment to good land stewardship.”
USDA offers financial and cost-share assistance to producers interested in planting and maintaining buffers through the Conservation Reserve Program and the Environmental Quality Incentives Program. See <www.nrcs.usda.gov/programs/>