Dryland Crops: The Farmers
Dry Times on the High Plains Give Advantage to Minimal Tillage
- 2,400 acres
- permanent wheel rows
- sorghum, wheat (hard red winter), irrigated corn
- strip tillage in continuous sorghum
- summer fallow to gather moisture
- 18 inches annual precipitation
- clay and clay-loam soil types
Weed management highlights
Strategies: minimum tillage... reduced-chemical fallow... cultivation... herbicides (mostly preplant)
Tools: cultivators... rotary hoe... disk-steer guidance system... stubble mulch plow... chisel plow
Jim Cavin tried no-till farming in his 1.5-mile long fields of grain, but finds that mulch tillage works much better in his heavy clay loam soils. And after three consecutive dry years then a stiff cost hike for irrigation-pump natural gas in early 1997, he believes that maintaining residue year-round and managing soil conditions at planting are more critical than ever.
With no-till, he encountered increasing weed problems, despite his use of recommended herbicides. He also was unable to create a favorable seedbed environment during the harsh High Plains springs. 'I lost out on this untilled clay loam soil that always seemed to be too hard or too wet or too dry,' Cavin recalls. 'With mulch tillage, I can scrape together enough loose soil and residue to give the seed moisture, air and a chance to survive.'
He combines mechanical weed control with three tillage jobs: fallow management, furrowing of crop beds and 'diking' (see Dale Artho).
Continuous dryland grain sorghum is his main crop. Forty-inch rows give plenty of room for residue dispersion. Compared with 30-inch rows, the spacing gives crop roots more soil moisture to scavenge, but lessens the canopy shading effect to suppress weeds.
He plants sorghum deep enough to find moisture. Residue managers - finger wheel attachments ahead of his planter opener - clear residue out of the row area. Cavin bands or broadcasts preplant broadleaf herbicides, depending on weed and residue conditions. Dry surface soil often helps to keep weed pressure low through the early weeks of sorghum growth. Cultivation takes care of grasses that find enough moisture to emerge, but he has to hit large-leafed devil's claw weed with a mix of atrazine and crop oil.
Cavin makes his first weed-control pass with a 40-foot John Deere standard rotary hoe. The tool has close-spaced wheels that can plug in high-residue situations. But it works for him in the untilled sorghum residue primarily because of relatively low yields - 2,500 pounds per acre on average. That's about as much residue as an Illinois farmer would get from a 45-bushel-per acre corn crop. Further decreasing the residue-tangling potential in the widely spaced rows is a spring-time pass with a rolling stalk chopper.
'I drive the hoe at 10 miles per hour and watch closely for crop and weed impact,' says Cavin. 'On a good, long day I can hoe 400 acres.'
He begins to cultivate as soon as the sorghum plants can tolerate soil flowing against them. He pulls three sweeps between the wide crop rows with his 12-row, high-residue cultivator. A 24-inch flat sweep slices down the middle, while two 12-inch low-profile sweeps run to within 4 inches of the row on either side. That provides a 4-inch overlap within the row for extra weed-cutting action. He assembled the rig with Roll-A-Cone components on a Bigham Brothers toolbar setup. Both firms specialize in regional tillage equipment.
'This tool will last for a long time, and I figure I spend about $2.50 an acre for diesel to pull it,' says Cavin.
He's had good success with the unit, even when volunteer sorghum, annual grasses and the seeded sorghum have all been 5 to 6 inches tall. If his herbicides don't work, he'll go through a second time.
He budgets one cultivation as a no-cost operation because of his need to 'dike' the fields. Each depression is about 4 feet long and 6 inches deep.
At 4 mph max, it's not a quick field pass. But it's necessary. 'We get most of all our rainfall in summer. You have to have these reservoirs, or you lose it,' says Cavin.
An Orthman Tracker disk-steer guidance system keeps the cultivator aligned with the rows. On first pass, fist-sized bulb weight sensors drag ahead of the cultivator in a furrow made at planting. The sensors can detect a change in orientation between the cultivator toolbar and the furrow. Their movement is picked up in the sensor box, which then triggers automatic adjustments by the rear-mounted disks. He switches to plant-sensing wands on second pass, when stalks are stiff enough to be detected by the wands.
Weed pressure in sorghum is usually light, rarely requiring more than a single cultivation. His sweep cultivator takes out the weeds and volunteer corn. He makes the pass as early as possible to avoid root pruning and to cover as few milo shoots as possible. Cavin tries to maximize the secondary grain heads. In '96, he planted about 32,000 plants per acre but ended up harvesting an estimated 55,000 to 60,000 stalks per acre. Yield was 6,800 pounds per acre, with the plants supporting two or three heads each.
Wheat follows a year of moisture-conserving fallow, a no-crop season that builds up soil moisture for the following season. After fall harvest of corn or sorghum, the field is left untouched throughout the winter. When spring rains stimulate weeds, Cavin controls them using a chisel plow outfitted with 18-inch sweeps on 12-inch centers. He works the soil each time rain causes a new surge of weed germination, usually three or four times per summer. It's been fewer in the recent dry years. He plants wheat about the first week of October.
With no livestock, he derives no grazing benefit - a common way that other farmers in the area get double use from wheat fields. But the earlier-planted grazing wheat also takes more moisture. 'Wheat should help hold snow, but we've not been having enough moisture to get the wheat tall enough to stop much snow, and we've not been having much snow to be caught.'
He controls weeds at first tillage after wheat harvest with a stubble mulch plow. It has straight shanks on 40-inch centers with 42-inch flat blades. The replaceable V-blades attach in a way similar to the much larger wide-blade sweep plow. Cavin made the 40-foot-wide tool himself and pulls it with a 200 HP tractor. Running depth is 2 to 3 inches at about 5 mph.
He makes succeeding fallow passes with a chisel plow equipped with 18-inch sweeps on 12-inch centers. Cavin uses this tool only for weed control and feels it causes less compaction than the much heavier wide-blade sweep plow. He uses the chisel plow as soon as the soil dries enough to avoid compaction but before the soil becomes too hard and weeds become too large.
He leaves his corn stalks untilled and unchopped over winter to hold soil in place and to minimize residue loss from tilling. 'I have to have standing stalks to stop the blowing snow of February and March,' Cavin explains. 'Otherwise, it just keeps on going.'
He's been managing residue more carefully for several years to depend less on irrigation water. It now appears he started early on a path others will need to walk, too. When moisture was relatively abundant, clean tillage of weeds worked because there was more groundwater available and farmers could afford to pump it.
Three years of drought - when the area received only about half the 18 inches per year it used to get - continues to draw down underground water supplies. Then in early '97 he received notice that the price of the natural gas that runs the pumps was increasing 44 percent.
These conditions confirm his determination to find effective, low-cost dryland strategies.
Judging subsoil moisture adequacy at planting time is a critical part of dryland farming. Cavin is developing his diagnostic skills using a steel probe to detect when there's enough soil moisture to raise corn in his non-irrigated fields. This 'penetrometer' is a carbon steel bar with a small round ball on the bottom. If he can push it down 5 to 6 feet, he knows he's got enough moisture for corn, which is less drought-tolerant than grain sorghum. Rains during the season have to provide the rest of the moisture.
Weed pressure in corn comes from kochia, a tough weed that herbicides won't control beyond an inadequate 75 percent. Cavin plows before planting to bury the weed seeds. He's using some new corn seed from lines that are resistant to grass herbicides. He looks to these chemicals for control of johnsongrass and sandbur grass.
Another way to make better use of water is to use a single irrigation system on two crops on different furrowed fields. This limits water use and spreads out the cultivation window to prevent the usual early summer weed pressure overlap.
'In '96 I planted 100-day corn on April first and had it in black layer on the first of August,' Cavin says. Yield was about 200 bushels per acre. 'Then I shut that pump down and diverted the water to a late sorghum field that I planted in June. The crop was just at the fill stage where moisture will improve the yield.'
Some farmers in the region rely on extensive herbicide applications with just one pass of a sweep plow, or extensive tillage with repeated disking, subsoiling and field cultivators. Some still burn their field residue. 'Change comes slow here,' Cavin acknowledges, but drier conditions call for innovations. He's convinced he'll make money over the long haul by learning new ways to manage residue with mulch tillage and limited herbicides.