Tillage techniques can be designed to help earthworms build tunnels a certain way--and thus help protect groundwater supplies from fertilizers and pesticides, ARS lab studies have found. In farm fields, worm tunnels help crops by loosening, draining and aerating soil, providing paths for roots and mixing in organic matter, the worms' food supply. The tunnels also help keep soil water free of harmful chemicals by harboring microorganisms that degrade pesticides and fertilizers. Worms dig these tunnels simply to find organic matter to eat. But the new study found tillage can affect the location of the worm's diet, with implications for groundwater. In lab studies with a common earthworm, Aporrectodea tuberculata,researchers discovered that worms tunnel at random until they find food. Subsequent food searches follow patterns that vary by tillage. No-till or reduced tillage, which leaves crop residue on the surface, encourages a network of vertical burrows and depressions. This tends to funnel water rapidly downward through soil layers, reducing the water's opportunity to remove fertilizers and some other chemicals in soil. Increased tillage leads to a less desirable pattern: horizontal and meandering tunnels. Water moves more slowly, increasing the odds it can bring along chemicals. The researchers plan field studies aimed at finding new ways for using tillage techniques to encourage vertical earthworm burrows.
Soil and Water Management Unit, St. Paul, MN
Dennis R. Linden, (612) 625-6798, dlinden@soils.umn.edu

A natural enzyme that helps chickens and pigs retain their diet's phosphate could be closer to widespread use as a commercial feed additive. Adding the enzyme, phytase, to animal feed would help improve water quality by reducing phosphate amounts and runoff in manure. Feeding studies indicate hogs and chicks retain up to 60 percent of their diet's phosphate when phytase is added. This means less gets excreted into the environment. But commercial use of phytase in the U.S. has been limited. Mainly, that's because the enzyme breaks down when exposed to the high temperatures used to process feed into pellets. Now, ARS scientists are developing a heat- resistant version of phytase from Aspergillus fungi. One fungal isolate produces a phytase capable of withstanding 160o F for several minutes. But it lacks the shelf life and other desirable properties of a commercial phytase produced by A. niger. The scientists are using recombinant techniques to design a superior enzyme that has the best of both worlds: greater heat stability and longer shelf life. They are seeking a commercial collaborator to help further develop superior phytase enzymes for use in soybean meal and other feeds.
Commodity Utilization Research Unit, New Orleans, LA
Edward Mullaney/Jaffor Ullah, (504) 286-4364, emul@nola.srrc.usda.gov/aullah@nola.srrc.usda.gov

Buffer areas called riparian zones protect stream water from herbicide runoff, ARS researchers have found. They conducted a 3-year experiment testing a standard buffer designed by USDA's Natural Resource Conservation Service. The buffer has three subzones. The first extends about 15 feet from the streambank and is planted with native and hardwood trees. The second subzone, about 20 feet wide, is planted with conifers, hardwoods and other tree species that can be periodically cut for timber. The third subzone, closest to the crop field, is a swath of thick-stemmed grasses. In their study, ARS researchers applied two common herbicides, atrazine and alachlor, to a corn field. They then tracked the chemicals' movement into a nearby grass and riparian buffer at the field's lowest end. At the corn field's edge, they detected concentrations of atrazine (34 parts per billion) and alachlor (9 ppb). But near the stream, they only detected the chemicals at concentrations of 1 ppb or less. This indicated that the buffers worked--broke down, soaked up or otherwise removed herbicide in both runoff and shallow groundwater. Runoff can also harbor excess fertilizers, sediment and other pollutants that endanger water quality.
Southeast Watershed Research Lab, Tifton, GA
Richard R. Lowrance, (912) 386-3462, rlorenz@tifton.cpes.peachnet.edu

Thwarting next year's pink bollworms by burying the whole stalks of this year's harvested cotton plants-- instead of shredding the stalks--reduces on-farm energy use by nearly 70 percent. That's according to preliminary ARS experiments with a new, whole-stalk-burial tool that is mounted to a tractor. After harvest, cotton growers in California, Arizona and Texas are required by law to plow down their fields. That prevents the plants from resuming growth in the spring and provides convenient housing for newly emerged pink bollworms. ARS is testing a device that buries the stalks with only one or two passes instead of the normal seven. This reduces soil compaction. The implement presses the stalks into a 6-inch-thick rope, then buries the strand. Crop yields from research plots cleared with the new implement equaled those from fields cleared with conventional tools. ARS engineers are making key modifications to the device under a 3-year cooperative research and development agreement with the manufacturer, Pegasus Machinery Co., Tucson, AZ. Buried strands may take longer to decompose than conventionally shredded stalks. Scientists want to determine if this will prolong the availability of organic material fed on by microorganisms that enrich arid soils in cotton-growing regions of the southwest, including California, a leading producer of this crop.
Western Integrated Cropping Systems Research Unit, Shafter, CA
Lyle M. Carter, (805) 746-8004, lcarter@lightspeed.net

Last Updated: February 18,1998
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