Sometime in the past 15 years, American farmers crossed an auspicious environmental boundary: They began reducing the level of atmospheric carbon dioxide rather than adding to it. CO² is one of the greenhouse gases thought to cause global warming. A new ARS study shows that U.S. farmers have shifted from being net producers of carbon dioxide to net accumulators of carbon, in the form of valuable soil organic matter. An ARS soil scientist discovered the difference after a thorough search of published reports and surveys for several major crops and comparing 1940 to 1990 conditions. The analysis, aided by other research nationwide, showed the changeover was due largely to farmers' increasing abandonment of a cherished symbol of past American agriculture, the moldboard plow used to break up the prairies. By 1993, farmers used moldboard plows on only 6 to 9 percent of wheat, soybean and corn, according to USDA statistics in the study. The plow inverts soil to a depth of 8 to 12 inches. The inversion buries recent stubble and other unharvested crop residue deep into the plow layer, where microbes tend to decompose it into carbon forms easily converted to CO². This CO² can escape to the atmosphere. As farmers put aside the moldboard plow, they leave nearly all of the residue on the soil or within a depth of 4 inches. For example, corn and grain sorghum farmers are returning twice as much crop residue to the surface as there was in 1940. Here, the residue readily decays to organic matter, a more stable carbon compound and a key property of the black, fertile prairie soil.
Soil and Water Management Unit, St. Paul, MN
Raymond R. Allmaras, (612) 625-1742, allmaras@soils.umn.edu

A new and improved tool developed by ARS scientists swiftly measures a field's soil strength, giving farmers and researchers a quick way to tell if plant roots will have a hard time pushing down into the soil. This information helps farmers decide what type and depth of tillage is best for their fields. The new multiple-probe soil cone penetrometer tests soils for compaction or layering that restricts root growth. Dense, high-strength soil tends to confine root growth. Heavy agricultural equipment can also cause this condition. Loose, low-strength soil provides the best condition; it lets roots penetrate downward and reach moisture during summer dry spells. The tractor-mounted probe measures soil strength across an entire row in about 1 minute—a great timesaver. Manual one-probe devices require five insertions to obtain the same data and can take 10 minutes per row. Another improvement: The new version is more sensitive than previous models. It reads depth to the millimeter and penetration force to within 0.1 pound per square inch. ARS scientists have used the device to measure soil compaction in several soils throughout the Southeast.
National Soil Dynamics Laboratory, Auburn, AL
Randy L. Raper, (334) 844-4654, rlraper@eng.auburn.edu

A hairy vetch cover crop and corn residue left from not plowing create a double mulch for crop fields, saving on chemical weed killers and commercial fertilizers. This double mulching keeps soil moist and smothers grass weeds, the principal weed type in farm fields. Preliminary data from 1998, the second year of a 3-year study at Beltsville, MD, suggest the practice could reduce the amount of atrazine used nationally to control grass weeds. American farmers use 250 million pounds of atrazine annually. Atrazine is a pre-emergent herbicide—that is, it's used as a precaution before planting. It and other pre-emergent herbicides are potentially more of an environmental hazard than postemergent herbicides, used when weeds appear after planting. Preliminary results of assessing herbicide fate in no-till corn also indicate that hairy vetch reduces the loss of herbicides in runoff, but several years' data will be needed before a quantitative value can be given. The researchers' data also show that nitrogen-producing cover crops like hairy vetch can reduce nitrogen fertilizer use without sacrificing yields. Similar preliminary findings from an ARS demonstration project at Beltsville suggest that the hairy vetch system is most profitable to farmers. The new data show that vetch also reduces downward leaching of metalochlor, a common herbicide for cornfields. The next phase of the study, to run 5 additional years, is named CIMASS, for Cover Crop Impact on Nitrogen and Weed Dynamics To Minimize Agrochemical Use in Sustainable Systems. This phase will lead to detailed recommendations on how farmers can rely more on postemergent herbicides and apply other cost-effective techniques to control weeds with the least loss of herbicides to the environment. Commercial herbicide-resistant corn varieties will be tested.
Environmental Chemistry Laboratory, Beltsville, MD
Ali M. Sadeghi/Allan R. Isensee, (301) 504-6693/(301) 504-5297, asadeghi@asrr.arsusda.gov/
aisensee@asrr.arsusda.gov
Weed Science Laboratory, Beltsville, MD
John R. Teasdale, (301) 504-5504, teasdale@asrr.arsusda.gov

An ARS-designed rainfall simulator has been setting the stage for what will probably be the largest outdoor study of the movement of coliform bacteria and Cryptosporidium parvum, a protozoan parasite, in rain runoff and soil water. The simulator has a boom that flexes as the land's slope changes, keeping the "rain" the same distance from the soil up and down the slope. The simulator will help scientists trace water movement to track possible routes for bacterial pathogens and for C. parvum, which caused an outbreak of illness from drinking water in Milwaukee in 1993. The study uses two of six lysimeters built by the U.S. Nuclear Regulatory Commission to study storage options for low-level radioactive waste. These lysimeters are giant blocks of soil isolated for contained outdoor studies. The NRC used empty tanks as stand-ins for radioactive waste and turned the sites over to ARS after the experiments were finished. Each lysimeter is above the water table and lined with plastic to prevent soil water from leaching in or out. Each is about 70 by 40 feet square and 10 feet deep. ARS scientists are testing two different soils and two different slopes in the lysimeters. From earlier studies, the ARS scientists have preliminary data indicating that bacteria are more likely to be a problem in groundwater, while Cryptosporidium is more likely to contaminate surface waters. Next year, the scientists will begin adding Cryptosporidium in manure and monitor its movement, along with that of native coliform bacteria which will be used as surrogates for pathogenic bacteria such as E. coli O157:H7, which has caused foodborne illness.
Environmental Chemistry Laboratory, Beltsville, MD
Daniel R. Shelton, (301) 504-6582, dshelton@asrr.arsusda.gov

A new device called a biosensor will help farmers and regulators detect herbicides in soil and water. In only minutes, the new invention identifies traces of herbicides residues by using a chlorophyll-protein reaction center complex that measures oxygen levels. To use the biosensor, the farmer or regulator passes a soil or water sample through the device. If the sample solution contains an herbicide, the chemical will react with the biosensor's proteins and inhibit oxygen production. This information is relayed to a computer, which displays the data in graph form. The biosensor can only measure herbicides that inhibit photosynthesis, such as diuron, atrazine, simazine, ioxynil, bromoxynil and dinoseb. This group of herbicides constitutes about 50 percent of all herbicides used in agriculture. The test is ultra-sensitive. Its detection limits are similar to or slightly better than the more complex, highly sensitive ELISA test, which is antibody-based. The biosensor works well at room temperature. Its membrane is stable for up to about 40 hours and can be reused within that period for any number of measurements. ARS scientists codeveloped the biosensor with scientists from the Czech Republic and Italy through a grant supported by the North American Treaty Organization. Once commercialized, it should be economical and easy to use—distinct advantages over currently available herbicide detectors.
Vegetable Laboratory, Beltsville, MD
Autar K. Mattoo, (301) 504-7380, amattoo@asrr.arsusda.gov

ARS-designed seed-delivery packages could be an inexpensive, natural way to revegetate overgrazed and desertified land, such as areas in the Jornada Experimental Range in New Mexico. The Jornada is in the northern part of the Chihuahuan Desert, one of the driest spots in the country and the largest desert in North America. In each package, seeds are tucked into three little pipes, which in turn are set within a larger pipe. The packages, which cost 75 cents each, are staked in rills often less than 4 inches deep to await a rare event in the Jornada: rain. If enough rain falls, a streamlet with sufficient force will break through crepe paper covering both ends of the lowest seed pipe. Seeds then flow out through a mesh screen on the end of the outer, larger pipe. If the rain continues, the streamlet rises, freeing seeds from the middle pipe—and so on. Seed is released only when rain falls. This ensures that all the seed is released only when there is enough rain to spread it far downstream. The rain also ensures that seeds are deposited in moist soil with a mulch cover of grass stem litter naturally carried by streamlets. The scientists are monitoring results to see if stream-seeded plants eventually spread to cover large areas of bare ground.
Jornada Experimental Range, Las Cruces, NM
Jeff Herrick, (505) 646-4842, jherrick@nmsu.edu