Hard soils that restrict root growth and reduce crop yields in the southeastern coastal plains can be overcome if producers use specialized deep tillage to loosen the soil. But on a per-acre basis, deep tilling costs an extra 2.5 gallons of fuel, adds a quarter hour of labor, and requires a large, 200-horsepower tractor. To help producers make well-informed decisions on whether to deep till, ARS and Clemson University researchers linked knowledge of soil hardness at planting to potential yield losses. To predict yield loss for intensively managed corn and soybeans, the study combined data on soil strength measurements at the beginning of the growing season with rainfall amounts at critical times in plant growth. It included treatments that either had not been deep tilled or had been deep tilled from 1 day to 3 years before planting. For Rains sandy loam soil, predicted yield losses ranged from 20 to 50 bushels per acre of corn and 16 to 26 bushels per acre of soybeans for each 10-atmosphere increase in soil strength. An atmosphere is 14.7 pounds of pressure per square inch of soil.

Coastal Plains Soil, Water, and Plant Research Center, Florence, SC
Warren J. Busscher, (843) 669-5203, ext. 105, busscher@florence.ars.usda.gov

Reducing sediment-laden runoff and improving water clarity have revitalized two Mississippi freshwater lakes as good sports fisheries. The increased water clarity boosted plankton growth, necessary to support bass populations that were lacking before the renovation and restocking. Natural oxbow lakes of the Mississippi Delta, long known for their productivity and recreational value, have declined in popularity because of poor water quality and reduced plankton growth. Research shows that cultural best management practices (BMPs) on nearby farms—in addition to structural measures—may be needed to improve fisheries in these lakes that were formed by meandering rivers and protected by nearby watersheds. Scientists were able to successfully reintroduce sports fish in the two lakes whose watersheds were protected with both culture-based BMPs—like conservation tillage and cover crops—and structural BMPs. The latter included grade stabilization structures like tall fescue grass filter strips and riparian forest buffer zones to reduce waterflow speeds. But structural BMPs used alone on the third lake didn't improve water quality enough to elicit an ecological change.

National Sedimentation Laboratory, Oxford, MS
Scott Knight, (662) 232-2935, knight@sedlab.olemiss.edu

An ARS-developed portable rainfall simulator (PRS) is helping scientists establish soil phosphorus threshold levels as local, state, and federal agencies gear up to curb the nutrient's runoff into rivers, lakes, and other water systems. In fresh waters, excessive phosphorus causes eutrophication, which triggers massive algal blooms whose subsequent decay can deprive aquatic life of oxygen. Ultimately, this impairs the quality of that water for drinking and recreation. Scientists are using the PRS to study how runoff carries phosphorus from crop fields, particularly when phosphorus-rich manure has been applied at levels exceeding the amount that the soil or plants can retain. The PRS involves pumping water from a tank on a customized trailer or pick-up into a spray nozzle attached to a 10-square-foot aluminum frame. The nozzle uniformly showers the underlying soil at a controlled rate until runoff occurs for collection, weighing, and analysis. As soil phosphorus increases, for example, PRS data has shown there is a threshold soil level above which potential for the nutrient's loss in runoff dramatically increases. Starting in the spring of 2001, scientists participating on the ARS-led National Phosphorus Research Project will use nearly two dozen PRS devices to standardize their collection of runoff data. This will take place on up to 50 different soil types at 20 research locations across the country. A key objective is establishing phosphorus management guidelines that simultaneously protect the environment and meet farmers' needs.

Watershed and Pasture Systems Management Research Laboratory, University Park, PA
Andrew Sharpley, (814) 863-0948, ans3@psu.edu

The amount of soluble cadmium (Cd) in soil can be predicted, based on soil pH and total Cd content. That's the finding of a Cornell University-Ithaca/ARS study of 64 soils collected from U.S. and Canadian fields with and without known Cd contamination. The purpose of the study was to understand which, if any, soil properties (like pH, soluble and total organic matter) affect the solubility of Cd in soils. A naturally occurring trace element, cadmium is found throughout the environment. It is a potentially toxic heavy metal with no known requirement by living organisms. It is most readily taken up by plants in its soluble form as it is drawn in through the roots and deposited in edible portions like stems and leaves. In animals, Cd accumulates mainly in the kidney and liver. At high levels, it can reach a critical threshold and lead to serious kidney failure. Many human activities—like land applications of sewage sludge, industrial sludge, manure, or phosphate fertilizer—increase soil Cd and can sometimes cause contamination. In the 64 soils studied, the amount of soluble Cd ranged more than a thousandfold, from 0.03 to 182 micrograms per liter. The solution pH, which ranged from 3.5 to 8.1, was the main determining factor—along with total Cd content—controlling solubility.

U.S. Plant, Soil, and Nutrition Laboratory, Ithaca, NY
Wendell A. Norvell, (607) 255-8808, wan1@cornell.edu

Linking irrigation to crop temperature can improve the efficiency and profitability of water use, thus optimizing crop yields and conserving natural resources. High crop temperature—a good indicator of crop water stress—can be measured accurately within each area of a field using noncontact infrared thermometers (IRT) on center-pivot irrigation machines. Commercial IRTs are inexpensive and easy to use, making them an attractive alternative to costly, research-grade sensors. ARS scientists spaced 26 IRTs along a center-pivot system modified to apply irrigation water on 396 plots, each about 30 feet square. Some plots were well irrigated, while others were left dry. Soil temperature differences of up to 14 degrees between irrigated and dry plots were easily detected with the IRT array. Surprisingly, the same treatments on multiple plots of the same soil type showed temperature variations of as much as 6 degrees. So water stress caused by elevated soil temperature can vary, even across a single soil type. This shows the importance of adjusting for variation in crop water stress while managing irrigation. Applying the correct amount of water only when a plant's temperature indicates it's needed makes possible a more effective stewardship of the nation's scarce water resources.

Coastal Plains Soil, Water, and Plant Research Center, Florence, SC
E. John Sadler, (843) 669-5203, ext. 112, sadler@florence.ars.usda.gov

Best management practices (BMPs) keep pesticides from contaminating groundwater in the Mississippi Delta. Spearheaded by ARS scientists, the Mississippi Delta Management Systems Evaluation (MSEA) Project develops farming systems based on economical and environmentally sound BMPs. The project encourages implementation of many BMPs designed to slow surface water runoff and enhance the soil's processing and retention of farm chemicals. Such practices tend to increase water infiltration and reduce the potential for farm chemicals to leach into the soil, possibly harming groundwater quality, or seeping into relatively shallow water tables with subsurface connections to nearby bodies of water. From 1996 to 1998, ARS scientists collected groundwater samples from 622 shallow wells in the 7,000-square-mile Mississippi Delta MSEA area. They placed groundwater sampling wells in riparian zones along rivers and streams, as well as in corn, cotton, soybean ,and rice fields. Analyses of water samples showed only five pesticide detections. All were at very low levels—0.4 to 8 parts per billion. This confirmed that BMPs allow soil to slow down and process pesticides in upper layers, greatly reducing their below-ground seepage. The finding clears the way for further establishing the BMPs on a regional scale, with good probability of their adoption by farmers and landowners.

National Sedimentation Laboratory, Oxford, MS
Sammie Smith, Jr., (662) 232-2936, smith@sedlab.olemiss.edu

An intensive search for fumigants that can rid strawberry fields of soil-dwelling pests has revealed several promising compounds. They are needed as alternatives to methyl bromide, the widely used fumigant that is being phased out because it depletes the Earth's protective ozone layer. ARS scientists in California found that marketable yields of strawberries from some plots treated with a fumigant called InLine were from 95 to 110 percent of those from plots treated with methyl bromide. InLine is a combination of about 60 percent 1,3-dichloropropene and up to 35 percent chloropicrin, a chemical typically used in combination with methyl bromide. Delivered to fields in irrigation system lines known as drip tapes, InLine is the water-soluble version of Telone C35, a compound already approved for use—with certain restrictions—to disinfest strawberry fields before planting. Plots treated with chloropicrin alone, applied at the same rates as InLine, resulted in about the same yields. Typically, fumigants are pumped into the soil as a gas. Using drip-irrigation systems may reduce worker exposure to the chemicals and may also decrease the amount of fumigant needed.

Water Management Research Laboratory, Fresno, CA
Husein A. Ajwa, (559) 453-3105, hajwa@asrr.arsusda.gov

How much herbicide or fertilizer runs off farm fields to pollute streams and rivers may depend less on the amount of chemicals applied and more on other factors such as the properties of the chemicals applied, soil characteristics, farming systems, and how soon it rains after chemicals are applied. In a 5-year study on claypan soils in the Midwest, which are representative of 10 million acres in the United States, ARS scientists found that heavy rains soon after fertilizer application may pose the greatest risk for nitrogen losses from soil in the forms of nitrate and ammonium. Fertilizer was also more apt to run off when it was spread evenly and incorporated into the soil by tilling than when it was knifed into the soil surface in narrow bands. The herbicides atrazine and alachlor were more prone to runoff losses in a no-till farming system than when they were incorporated in a minimum-tillage system. In a study in northern Missouri watershed basins, scientists found that the properties of the agricultural chemical applied and the soil characteristics of the watershed were more important to water quality of streams than the amount of chemical applied. In watersheds with well-drained soils but high row-cropping intensity, herbicide concentrations were much lower in stream water than in watersheds with low to moderate row-cropping intensity and poor drainage. The effects were opposite for nitrate contamination of streams, with the highest contamination in watersheds with well-drained soils and high row-cropping intensity. Nitrate concentrations were higher because farmers in such watersheds have historically applied more nitrogen fertilizer, and because more of the stream flow in these watersheds originates from nitrate-contaminated groundwater. The information from these studies can help develop better management practices for specific farming regions to maximize the potential for water quality improvements.

Cropping Systems and Water Quality, Columbia, MO
Robert N. Lerch, (573) 882-9489, lerchr@missouri.edu

Peach growers might be able to cut back the amount of water and fertilizer they use, yet still produce plump, perfect peaches. A long-term, ARS-led study may help California peach growers save water and avoid leaching of excess fertilizer into the underground water supply. ARS scientists and their university colleagues are experimenting with the timing and amount of water and fertilizer that they apply to about 1,800 young peach trees in a research orchard at Parlier, CA. The study features young trees because very little is known about their exact needs for water and nutrients such as nitrogen, phosphorus, and potassium. The researchers are looking for differences in growth that result from delivering varying quantities of water and fertilizer through furrows, microjet sprayers, or drip-irrigation tubing. The scientists are monitoring data from more than 500 probes and sensors positioned in the orchard. And they're using a miniature video camera to spy on root growth. Findings should apply not only to peaches, but also to orchards of other stone fruits, including nectarines, apricots, and plums. California produces more of these crops than any other state.

Water Management Research Laboratory, Fresno, CA
David R. Bryla, (559) 453-3106, bryla@pwa.ars.usda.gov

With proper nitrogen fertilization and a no-till production system, Great Plains dryland farmers can grow crops continuously, reduce erosion, and improve the soil's ability to store carbon, ARS scientists found. Typically, farmers in the Great Plains grow rain-fed grain crops like wheat, corn, or barley one year and leave the land fallow the next. With conventional tillage, the fallow period is needed to allow enough water to accumulate in the soil to support the next crop. But this practice increases wind erosion of the soil and speeds decomposition of plant material, a process that releases carbon dioxide to the atmosphere. Researchers have long known that no-till, or planting directly into the previous year's crop residue without tilling, reduces erosion and makes more efficient use of water. They've also found that no-till enhances the soil's ability to store carbon, which helps mitigate global change by reducing the amount of carbon dioxide reaching the atmosphere. Now, ARS research has shown that nitrogen may mean the difference between economic success and failure when using no-till on the Great Plains. In several no-till studies lasting from 9 to 12 years, adding sufficient nitrogen fertilizer increased grain yields and improved water use enough to make continuous cropping feasible. The added nitrogen also increased the amount of plant material left as crop residue. Over time, the nitrogen/no-till combination led to increased soil organic carbon and improved soil quality.

Soil-Plant-Nutrient Research Unit, Ft. Collins, CO
Ardell Halvorson, (970) 490-8230, adhalvor@lamar.colostate.edu