With the pull of a string-operated weed whacker, corn and soybean farmers can save surface water from possible chemical contamination and cut crop production costs, too. ARS studies of the Goodwater Creek watershed in Missouri indicate runaway herbicides are more likely to wind up in surface water rather than groundwater. But farmers can slash their herbicide use--and expense--by applying the chemicals only in a narrow strip over the crop row, then using a weed whacker to mow weeds between rows of corn or soybeans, the researchers say. Four years of ARS field tests showed this technique reduced herbicide use by 60 percent, while producing crop yields equivalent to those from weed-free fields.
Cropping Systems and Water Quality Research, Columbia, MO
William W. Donald, (573) 882-6404

Trickle-L, an ARS-created Internet discussion group on drip irrigation, now links about 500 scientists, farmers, golf course managers, irrigation equipment manufacturers and others in the U.S. and abroad. Drip irrigation, also known as trickle or micro-irrigation, uses tiny sprayers or emitters to deliver precise amounts of water to plants. This can boost yields and reduce leaching of fertilizer and other chemicals into underground water. Since its launching three years ago, Trickle-L has become a convenient source of up- to-the-minute information and ideas on drip irrigation. Topics range from how to keep gophers from gnawing buried irrigation lines to the best irrigation techniques for asparagus and raspberries. Drip irrigation also can help home gardeners lower their water bills, the scientists say. Another plus: It helps avoid excessive watering that might damage homes, fences and other structures.
Water Management Research Laboratory, Fresno, CA
Thomas J. Trout, (209) 453-3101, ttrout@asrr.arsusda.gov

The first measurements of greenhouse gas emissions from holding ponds for livestock waste shows they can emit from 36 to 268 pounds of methane per acre (40 to 300 kilograms per hectare) a day, depending on factors such as time of day, water temperature and wind speed. The measurements will help adjust global change prediction models. They will also enable the development of farming practices that lessen emissions or their impact. For example, 268 pounds of methane per acre is enough to fuel electricity generation. Scientists measured the emissions last summer with an array of "sniff tubes" mounted on a barge in the ponds, called animal waste lagoons. Samples of methane, nitrous oxide and ammonia were automatically drawn from the tubes for analysis by laser spectrometers. So far, nitrous oxide emissions have not been detected over the lagoons, although similar equipment did pick up emissions over farmland. Methane and nitrous oxide are greenhouse gases that could cause global warming. Ammonia emissions may contribute to soil acidification and can redistribute nitrogen to other areas where it may be unwanted. Ammonia emissions ranged from very low to a high of more than 54 pounds per acre (60 kilograms per hectare) a day.
Southern Piedmont Conservation Research Center, Watkinsville, GA
Lowry A. Harper,(706) 769-5631, lharper@uga.cc.uga.edu

Machine-made channels in plowed fields may be moving more farm chemicals into groundwater than wormholes, rootholes and other natural channels prevalent in unplowed soils. Water with a chemical tracer and food coloring dye added was recently applied to plowed and unplowed fields. After excavating four 65- square-foot pits, ARS scientists photographed the stained flow pathways and then digitized the photograph for computer analysis. The analysis showed that "preferential flow" pathways are common in both plowed and unplowed fields. These pathways can move farm chemicals into groundwater much faster than normally expected. Analysis of the dye patterns revealed that the unplowed field had more biological byproducts from the breakdown of atrazine, a common herbicide, than the tilled field. ARS scientists now believe that organic matter in the natural channels of the unplowed fields promotes growth of high numbers of microbes in the soil. These microbes, in turn, can help break down chemicals. In comparison, the machine-made pathways lack the organic material and perhaps the microbial populations to degrade farm chemicals. Scientists are now attempting to link these dye patterns to movement of nitrate from nitrogen fertilizer. As for herbicides and other farm chemicals, any movement of nitrate away from plant roots results in an economic loss to the farmer and poses a potential environmental risk to groundwater quality.
Hydrology Laboratory, Beltsville, MD
T.J. Gish/D. Gimenez, (301 504-7490, tgish@hydrolab.arsusda.gov

Last Updated: July 14, 1997
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