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Much of the organic matter being lost from America's croplands may
literally be going up in a puff of gasas carbon dioxide. An ARS study
found that loss rates are fastest within minutes after plows break the
surface, letting oxygen into soil. Carbon is the backbone of the organic
matter that makes the black soils of the Corn Belt as fertile as they are.
The extra oxygen permeating the soil stimulates microbes to chew faster on
the organic matter. As a result, more carbon dioxide seeps into the
soil's air spaces and escapes during plowing, contributing to a potential
global warming. The study recorded carbon released from wheat fields
plowed in the fall. After 19 days, total losses of carbon were up to five
times higher than for unplowed fields. As much carbon escaped into the
air in the form of carbon dioxide as was added to the soil the previous
season by wheat crop residue left on the field. Losses can vary two- to
three-fold in a distance of 50 feet. These findings point to the value of
not plowing fields. But, when plowing is required, ARS scientists are
trying to put a dollar value on the losses to see if it's worth developing
sensors so tillage machines can disturb the soil less on parts of fields
most likely to lose carbon dioxide.
North Central Soil Conservation
Research Laboratory, Morris, MN
Donald C. Reicosky, (612) 589-3411
How much can a change in the use of farm acreage reduce soil erosion in
a watershed? A drop in cultivated acreagefrom 1211 to 579
acresdecreased soil erosion from agriculture by 42 percent on the
8.2-square-mile Goodwin Creek Experimental Watershed in the hills region
of north central Mississippi. That was the finding of ARS researchers who
compiled a wealth of data on rainfall, soil type, stream sediment, bank
stability and land use over 10 years. As a result, a study yielded a
picture for the first time of how changes in land usesuch as shifting
erosion-prone, cultivated land to pasture and forestcan protect soil
resources. On a yearly basis, the concentration of fine particles in
runoff water decreased from 2600 to 1200 parts per million.
National
Sedimentation Laboratory, Oxford, MS
Roger Kuhnle, (601) 232-2971
As herbicide is sprayed on a field, some of the herbicide's particles
drift into the air. ARS researchers sampled rainwater over four years
to find how much of an airborne herbicide like atrazine will "wash out" in
rainstorms that unexpectedly occur after herbicide is sprayed on farm
fields. An analysis found herbicides in the rainfall are at levels safe
for drinking waterless than one microgram per liter. That compares to the
federal minimum of three microgram per liter for atrazine. All the water
sampling was done at two sites in the Walnut Creek watershed of central
Iowa after each rainstorm. Herbicidesincluding atrazine and
metolachlorappeared primarily in samples during the spring, when they were
being applied. Nitrate from nitrogen fertilizer was detected in samples
throughout the year. Except for one sample, nitrate levels in rainwater
averaged 1.5 parts per million throughout the year. Over a year, nitrate
deposits totalled over 11 pounds per acre. Such research on herbicides
and nitrate deposited in rainfall will help develop efficient application
methods for farmers to protect rainwater.
National Soil Tilth Laboratory, Ames,
IA
Jerry Hatfield, (515) 294-5723
Chemicals leave behind molecular "fingerprints" in resins that help
pinpoint contaminants in soil, water or food. ARS researchers worked
out the resin imprints to get a first-step identification of herbicides in
about 10 minutes. That would make it possible to quickly separate
extraneous chemicals and zero in on the specific chemical in further
analytical procedures. In tests, researchers mixed triazine herbicides
with compounds that hardened into tough resin. When the resin was ground
into particles, imprints of the herbicides' molecular structure stayed on
the particles' surface. If a water sample containing triazine herbicides
is mixed with the particles, the chemical molecules in the water fit into
the imprints like pieces of a puzzle.
Food Animal Protection Research
Laboratory, College Station, TX
Larry H. Stanker, (409) 260-9306
Last updated: October 29, 1996
Return to: Quarterly Report
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