Sustaining Agriculture in Drought
In the Lower Grande Valley, ARS soil scientist Joe Bradford
(standing) and Mexican farmer Fernando Gomez Gomez assess the effects of wind
erosion, which research shows can be reduced if conservation tillage farming is
Punched by a 4-year drought and by insects that ravaged the cotton crop in
1995, Texas agriculture has been reeling. But new conservation tillage systems
have taken out some of the sting. A team of scientists with the
Agricultural Research Service in
Weslaco, Texas, developed and tested the new systems.
They are the first designed for the soil and climate of south Texas, where
growers plant more than a million acres of cotton, grain sorghum, corn, and
Keeping some of the previous crop's residue on the soil surface and reducing
use of plows and other tillage equipment are central features of conservation
This approach makes soil, water, and other natural resources more
sustainable over the long haul. Often, it allows growers to reduce
costssuch as fuel and laborwhile keeping yields acceptable.
Crop residue-based systems "have been accepted in the Midwest for 15
years," says soil scientist Joe Bradford. "But those systems won't
work here. We have vastly different soils and climate, and growers here need
solutions that take those differences into account."
For example, says agronomist James Smart, crop residue is harder to come by
in south Texas. It decomposes much more rapidly in the semiarid, subtropical
climate than in the humid Midwest. South Texas also lacks the Midwest's
deep-freeze temperatures that hold down weed growth in winter.
"In Texas, weeds must be controlled year-round, and that has meant
several tillage trips to plow them under," says Smart. He and Bradford are
based in the Conservation and
Production Systems Research Unit that is part of ARS'
Subtropical Agricultural Research
Laboratory at Weslaco.
Rows of no-till cotton were planted directly into this unplowed
cornfield. Note the abundant residue between rows that helps prevent moisture
loss and weed growth.
No one knew drought was on the way in 1992. That's when Bradford, Smart, and
agricultural engineer Robert Rektorik (now retired) began developing and
testing new conservation tillage systems for dryland and irrigated farms in the
Lower Rio Grande Valley of Texas. Earlier, ARS researchers in Bushland, Texas,
pioneered conservation systems for dryland farms hundreds of miles north in the
The Weslaco researchers found ways to maintain crop residue cover and
control weeds with little or no tillage. Through field trials, they found that
the new systems could increase net returns an average of $30 to $50 per acre
for major crops like cotton, sorghum, and corn.
Results at some test plots are more dramatic, largely because drought is
harshest on conventionally farmed crops. On dryland cotton plots at Mission,
Texas, conservation tillage from 1993 through 1995 netted $35 per acre,
compared to a loss of $32 on conventionally tilled plots. At irrigated Weslaco
sites, conservation-tilled cotton netted an average of $82 per acre.
Conventionally tilled plots lost $110.
The researchers also found strong economic benefits with irrigated and
dryland sorghum and irrigated corn. They measured per-acre corn yields up to
130 bushels in conservation tillage plots. The area average is about 70
"We have also noticed," Smart says, "that when we grow corn
after cotton, this breaks the cycle of a cotton disease called root rot."
Similar systems, the researchers found, can work elsewhere in south Texas
and in the part of the lower Rio Grande in northeastern Mexico.
Agronomist Jim Smart and Mexican farmers Miguel Morales Beltran and Hector
Rodriquez Mediola discuss the 1996 drought that caused this irrigation ditch
near Rio Bravo, Mexico, to dry up.
Conservation Tillage Gets a Push From Nature
Drought has given new urgency to the Weslaco studies. Smart worries that
"if farmers don't use conservation tillage, parts of south Texas and
Mexico could become a dust bowl." He hopes its adoption will usher in an
era of greater sustainability for the region's agriculture.
Texas normally ranks near the top nationwide in producing sorghum, citrus
and vegetable crops, livestock, and cotton. But normal years have been rare
since 1988, when crop-withering drought was soon followed by freezes that
killed most citrus trees. The industry had to rebuild from the ground up, by
planting new trees.
Cotton, sorghum, and corn make up about half the typical annual $400 million
crop value in the lower Rio Grande in Texas. But drought and 1995's cotton crop
failure triggered a dramatic turnabout in planting patterns.
In 1995, valley growers seeded 360,000 acres of cotton and 306,000 acres of
sorghum. In 1996, cotton slid to 181,000 acres, while sorghum jumped to
504,000, partly due to higher prices resulting from a drought-related drop in
grain sorghum and corn production in Mexico. But because drought also raises
the threat of aflatoxin, a fungus-based grain contaminant, valley farmers in
Texas planted only 20,000 acres of corn in 1996, down from 40,000 acres the
The valley's cotton and sorghum are planted in early spring and harvested in
mid- to-late summer. Some growers replant these fields with corn that matures
in December or January. With conventional farming, growers make between 7 and
16 trips over the fields.
The stalk-puller attachment drawn through this cotton test field near Weslaco,
Texas, by field technician Victor Valladares plucks out the whole plants, roots
Conservation tillage trades most of those trips for a soil blanket of
leaves, stems, and stalks from previous crops. Less tillage means less soil
compaction. Plus, the residue shields the soil from heat, wind, and rain. It
keeps the soil cooler, cuts moisture loss from evaporation, and reduces labor
and fuel costs, says Bradford.
Even before drought tightened its grip, valley growers had begun voting with
their tractors: They now use conservation tillage on more than 100,000 acres,
Results from the ARS experiments have been key factors in these grower
decisions. Besides managing the test sites in Weslaco and Mission, the ARS
researchers have been cooperating with the John Deere Co. and a Mexican
growers' group on field trials in northeastern Mexico.
Drought Puts Conservation Tillage to the Test
As cotton and sorghum planting season arrived in the spring of 1996, south
Texas reservoirs were near empty. Since fall of 1995, some areas had received
only a few paltry inches of rain or none, instead of the normal 18 to 20
inches. Irrigation districts cut water allotments. Some towns restricted water
for drinking and other uses.
In several irrigation districts, growers had to make do with one irrigation
for the whole growing season. Many fields had been tilled several times to
build, maintain, and weed raised seedbeds, and "farmers had disked the
land to a fine powder," Smart says. To germinate their seeds, these
farmers had to spend their sole water allotment right after planting. Rain
would have to carry the crop to harvest. In many areas, rain wouldn't show up
Protective crop residue has been left on the surface of the low-till area at
left, where soil scientist Joe Bradford is standing. In contrast, conventional
tillage exposes the soil to wind and water erosion in the adjoining field where
agronomist Jim Smart kneels.
But some farmers had "banked" water in the soil over winter. They
had left the soil covered with residue and tilled it little or not at all. In
spring, they planted cotton or sorghum on small, low ridges built with
relatively light tillage equipment. Or they used no-till planters that placed
seed directly through the residue. Either way, the soil held enough moisture
from the preceding fall to germinate seeds and nourish tender seedlings. These
farmers could save their irrigation allotment for early summer, when growing
crops would most benefit.
Conservation tillage also benefits dryland fields, like those farmed by
Wayne Labar and son-in-law Charles Wadkins. They began using conservation
tillage about 4 years ago.
"Normally we get some good rain in February and May," Labar notes.
But from mid-December 1995 until June 1996, his farmland got only 2 inches.
"We didn't make a good crop. But we didn't lose money, because we didn't
spend a lot. We only worked the soil two or three times."
By summer 1996, dust storms had become more common. Some fields looked like
inland beaches, and adjacent fence lines and tree rows became sand dunes. Other
fields resembled jigsaw puzzles made of broken, unglazed pottery. This was a
result of rare but battering rains that sealed the soil surface, followed by
heat that baked and cracked the mud.
Even without drought, Smart points out, valley growers using conventional
systems have to replant at least some acres in most years.
"Rain shortly after planting can form a crust that seedlings can't
penetrate," he says.
Field technician Emilio Chavez drives a tractor-drawn stalk puller that uproots
plants after harvest. This prevents regrowth, water loss, and overwintering of
pests in cotton and grain sorghum fields.
When Smart traveled to northeastern Mexico in August to check the tillage
test sites, he was stunned. "The drought there is worse than in
Texaspossibly the worst in a hundred years." He estimates several
hundred thousand acres have been damaged in the states of Tamaulipas and Nuevo
Hector Rodriguez Mediola, one of the cooperators in the Mexico tests, grows
irrigated sorghum with conservation tillage near Rio Bravo in Tamaulipas. In
1996 when irrigation water was limited, he harvested about 2,000 pounds per
acrenot good, but something. Near the Rodriguez farm, conventionally
tilled fields yielded only sand, gravel, and rock.
But "Rodriguez' land wasn't blowing at all," Smart says. "In
fact, it gained topsoil." Crop residue had trapped some of the dust the
wind had carried from other fields.
Ten of the 12 conservation-tilled sites in Mexico fared better than those
farmed conventionally, though drought took a heavy tollespecially at the
dryland sites. Still, irrigated sorghum at the Rio Bravo sites netted estimated
per-acre returns of $157 with conservation tillage, which was 50 percent more
than with conventional tillage.
In south Texas, harvested cotton and sorghum plants will generally resume
growing throughout the relatively mild winter, robbing soil moisture needed for
spring and summer. Plus, growing cotton plants can serve as wintertime boll
In Texas, a plowdown law requires growers to shred and destroy all standing
residue after cotton harvest. The law was passed in 1987 after ARS entomologist
K.R. Summy and other Weslaco researchers proved the hazard of letting the
plantsand boll weevilssurvive the winter.
To control weeds in this no-till corn stubble plot planted with cotton, a
pre-emergence herbicide (Clomazone) for broadleaf weeds and some grasses and a
post-emergence contact herbicide (fusilade) for grass have been
Typically, farmers use a moldboard plow to kill both sorghum and cotton
plants. But the stalk puller is a new conservation tillage tool for doing this
in the lower Rio Grande Valley. Arrayed behind a tractor, stalk pullers
resemble huge tweezers with disk-shaped tips. They pinch sorghum or cotton
stalks at ground level and yank them out.
The stalk puller does this job for about $2 an acre and covers about 20
acres an hour. Using a moldboard costs six times more and takes about an hour
to cover 3 to 5 acres. "It's a lot harder to drag a moldboard plow or
heavy disk through the soil than to run a lighter piece of equipment over the
top," Smart says.
The Weslaco researchers' conservation tillage systems also reduce use of
heavy equipment by controlling weeds with herbicides.
"Every time you till or plow to control weeds, you're also planting
more weed seeds--as well as making the soil more vulnerable to erosion, our
most significant environmental contaminant," Smart says. "With
conservation tillage a grower relies more on chemical weed killers because
temperatures low enough to kill weeds seldom occur here during the winter.
Several effective herbicides are available. They are generally low in toxicity
to wildlife and beneficial insects, and they break down so quickly there's a
minimum hazard to water quality."
Hooded sprayers operated by field technician Victor Valladares direct herbicide
just to areas between rows of grain sorghum.
Growers Run Their Own Field Tests
Concern over weeds has been one reason for Texas growers' skepticism about
conservation tillage, popular in many areas of the nation for a decade or more.
Says grower Wayne Labar, "We have not had confidence in the chemicals
needed to replace tillage for weed control. But we've learned that they can do
Most valley growers probably took a similarly dim view of conservation
tillage 5 years ago, says Smart.
"In 1992, when I spoke about conservation tillage at a half-dozen
meetings, some farmers said switching would ruin them. They said, 'This isn't
the Midwest. This is dry country. We have to plow to make a crop here.'"
"They were right in thinking that Midwestern systems would ruin
them," says Smart. "Back then, they lacked some essential tools and
practices, such as the stalk puller. But a few pioneering growers at first, and
now more and more, are finding out for themselves that conservation tillage can
"We argued against conservation tillage," says Charles Loop. He
and his family grow mainly cotton and sorghum. The farm is about 1,200
irrigated acres near the banks of the Rio Grande near Brownsville, at the
state's extreme southern tip. It's so far south, you can peer north into Mexico
from some of Loop's fields, tongues of land formed by the river's twists and
Until 1989, the Loops plowed deeply and tilled often, like nearly everyone
else. Then, says Loop, "we got caught with a soybean crop that got hit
with an early freeze. So we planted cotton and sorghum through the dead soybean
plants." That was an experiment amid a crisis. It worked, and the Loops
gradually switched almost entirely to conservation tillage.
Agronomist Jim Smart is changing a planter's residue fingers-a tined wheel that
moves dense crop residue aside so that seeds can be sown in the soil
"The earthworms were the first thing I noticed. We hadn't seen them
before," says Loop. He thinks their passageways allow his cotton roots to
dig deeper than in plowed soil. "We don't follow any set rules. But as
long as yields are up and costs are less, we're going to stay with it."
Smart agrees there's no fixed recipe. "Each farm is different, and the
first year is the toughest. The grower may need to reduce tillage operations
gradually, rather than switch all at once. Residue is not built up yet, and
soil organic matter takes several years to increase."
Further, growers need to understand why the new systems work--to make the
most of them and avoid potential drawbacks.
For example, one drawback of surface residue is that it can tie up some of a
crop's fertilizer if broadcast over the field. So Smart recommends using
injector systems with liquid fertilizer. Pulled behind a tractor like a row of
fat hypodermic needles, injectors squirt fertilizer just beneath the soil
surface and near plant roots, with almost no waste.
Work to refine systems for cotton, sorghum, and corn will continue, say the
researchers. And since the valley is an important producer of broccoli,
peppers, and other vegetables, "we're going to be looking more at
possibilities in those crops," Bradford says. -- By
Jim De Quattro, ARS.
M. Bradford is at the USDA-ARS Subtropical Agricultural Research
Laboratory, 2413 E. Hwy. 83, Weslaco, TX; phone (956) 969-4859.