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Drought Management on Cropland Fields

Drought Management on Cropland Fields

by Robert Schiffner, Resource Conservationist
Natural Resources Conservation Service
Hays, Kansas

Whether it is a 5- to 7-year prolonged drought or a shorter 1 to 2 years, drought periods seem to be a regular cyclic occurrence. Planning for these occurrences is something farm managers need to keep at the forefront of their long-term planning process.

Drought management equals moisture management

Soil moisture management becomes a major issue for farms during drought periods. A well-known method of soil moisture management is leaving crop residue on fields to increase organic matter and decrease evaporation from the soil surface. Direct seeding also reduces the amount of tillage required and keeps the soil moist and less prone to erosion.

Soil moisture storage efficiencies of 40 to 60 percent are achieved when tillage is minimized or eliminated. The key to maintaining crop residue on the soil surface is minimizing or eliminating soil disturbance. Each tillage operation causes soil moisture and crop-residue loss.

Tillage Effects on Water Conservation

Assuming soil moisture is present, expect soil water losses from different tillage operations (Table 1) (Croissant et al. (2008)).

Table 1: Water Losses from different operations 1 and 4 days after tillage.
Operation 1 day 4 days
inches of water
One way 0.33 0.51
Chisel 0.29 0.48
Sweep plow 0.09 0.14
Rod weeder 0.04 0.22

Consider residue retention associated with moisture loss on tillage when residue must be retained on the soil surface. Use Table 2 to estimate stubble as a reduction of various operations. For example, if sweeps (24 inches wide) are used one time after harvest (10 percent reduction) followed by two rod weeder operations (2 x 15 percent reduction each), a 40 percent reduction occurs (Croissant et al. (2008)).

Table 2: Percent residue lost after using different equipment.
Operation % residue lost due to each operation
Spraying 0
Sweeps (24 inches) 10
Disk drills 20
Disk chisels 10
Rod weeder 15
Chisel plow - straight points 25
Chisel plow - twisted points 50
Tandem disk 3" deep 80
Tandem disk 6" deep 90
Moldboard plow 90-100
Overwinter weathering 15-25
Table 3: Water runoff when applied to no-till, disked and disked soil with straw cover
Time (mins.) No-till Disked Disked/Straw

Runoff inches/hour

15 Started    
18 --- Started  
20 0.8 1.4  
25 2.1 3.0 Started
30 2.4 3.5 0.4
40 2.4 3.5 2.4
Table 4: Maximum daily soil temperature at 2.5 cm depth comparing 0 and 3,000 pounds wheat straw per acre (lbs/ac)
Period Maximum Air Temperature
degrees F

Straw lbs/ac

0 3,000

Soil Temp, degrees F

Oct 7-11 77 76 67
Oct 12-16 75 78 68
Oct 26-30 67 70 62
Oct 31-Nov 4 66.8 69 61

Eliminating runoff can significantly improve water infiltration. Applying water under various field conditions shows that no-till and high levels of residue on the soil surface reduce runoff compared to standard dryland tillage systems (Table 3). During this experiment, simulated rain was applied equally on all plots. Treatments were no-till, disked, and disked with 3,000 pounds wheat straw per acre. Runoff began first on the no-till; however, runoff remained low throughout the experiment, compared to the disked (standard check) treatment and the treatment with straw cover. The no-till and disked/straw cover allowed more water infiltration than the disked treatment.

Soils with stubble cover reduce wind velocities at the surface and temperatures, reducing evaporation from the soil surface. Experiments at Akron, Colorado, indicate that water losses were 1.5 times greater on bare soil compared to soils with 3,000 pounds of wheat straw (Table 4) (Croissant et al. (2008)).

Cover Crops

Cover crops take up water (transpiration) when they grow, but prevent water losses from the soil surface (evaporation) after they are killed. The live or dead cover crop can also improve infiltration by reducing sealing and crusting of an otherwise bare soil surface. Evaporation reduction after a cover crop is killed only takes place if the cover crop is left as a mulch at the soil surface, not if it is incorporated by tillage.

Terminate growth of the cover crop early to sufficiently conserve soil moisture for the subsequent crop. Cover crops established for moisture conservation should be left on the soil surface until the subsequent crop is planted.

Water Use by Weeds

Weeds, just like cultivated crops, extract water usually in greater amounts per unit of dry matter than field crops. They are competitive for water and nutrients. Problem weeds may differ from one farm to another. The most prevalent weeds in dryland fields of western Kansas include kochia, Russian thistle, pigweed, rye, downy brome, and jointed goatgrass.

Need for weed control sometimes causes farmers to overtill fields until most of the residue is gone. Under dry-soil conditions and in low-rainfall areas, using sweep tillage tools and other reduced tillage practices can control most weeds without destroying a large amount of residue.

Conclusion

The best protection against moisture loss and wind erosion is a good protective cover of growing plants or residue.

Farmers must manage climate variability along with all other sources of risk. Farm managers need to understand the climate and weather patterns specific to the area they farm in order to make sound decisions.

There are several conservation practices that will assist farm managers with drought planning—conservation crop rotations, residue management such as mulch tillage and no-till, and properly timed cover crops.

Sources for Tables 1-4 and other references: Croissant, R.L., Colorado State University Extension agronomist and professor (retired); G.A. Peterson and D.G. Westfall, professors; soil and crop sciences. 9/92. Reviewed 11/08. Acknowledgement is given for support received from the Energy Conservation for Colorado Agriculture Program. <http://www.ext.colostate.edu.pubs/crops/00516.html>

For more information about drought planning and natural resources conservation, call or stop by your local NRCS office or conservation district office. The office is located at your local U.S. Department of Agriculture (USDA) Service Center (listed in the telephone book under United States Government or on the internet at offices.usda.gov). More information is also available on the Kansas Web site at www.ks.nrcs.usda.gov. Follow us on Twitter @NRCS_Kansas. USDA is an equal opportunity provider and employer.

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