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PNW CONSERVATION TILLAGE HANDBOOK SERIES
Chapter 3 - Residue Management, No. 4, August-September 1985


Storage of Overwinter Precipitation

Roger Veseth

Water is one of the most important yield-limiting factors for much of the dryland cropping region of the Pacific Northwest. The widespread drought conditions of the current crop year emphasizes the importance of available water. Since 70 to 80 percent of the annual precipitation in this region comes in the fall and winter, crop management decisions in the fall have the greatest impact on soil water storage potential.

One of the most effective tools growers have for increasing overwinter soil water storage is crop residue management. Surface residue increases storage efficiency in many ways. These include reducing evaporation, reducing runoff, which also controls soil erosion, and trapping snow. Surface residue also helps to maintain higher water infiltration rates in the surface soils through reducing the depth and frequency of soil freezing and preventing soil ''puddling" or sealing from raindrop impact.

STEEP researcher Bob Ramig has been evaluating the overwinter soil water storage efficiency of different fall residue treatments. Ramig is a USDA-ARS soil scientist at the Columbia Plateau Conservation Research Center near Pendleton, OR. Table 1 shows the benefits of leaving winter wheat residue on the surface overwinter at two Oregon locations. Over 2 inches additional soil water was stored with surface residue at Pendleton compared to where the stubble was removed by burning. There was little difference in soil water storage between standing and flailed stubble treatments.

Ramig's research also pointed out the soil water benefit of residue remaining on the surface after winter wheat is seeded in a reduced tillage system. With only 1,500 pounds per acre of spring grain residue on the surface after winter wheat seeding on fallow, 10 percent more overwinter precipitation (about 1.1 inches) was stored than with no surface residue under conventional winter wheat seeding. In a separate long-term study of a winter wheat-spring pea rotation, Ramig compared the effect of fall plowing with standing wheat stubble overwinter on soil water storage and crop yields. The study was conducted on a Walla Walla silt loam soil near Pendleton. An average of 2 inches more soil water was stored with standing stubble than with fall plowing. This additional soil water increased pea yields an average of 20 percent. Winter wheat yields also were increased by 5 percent the following years with stubble standing overwinter because the pea crops generally did not utilize all of the additional stored soil water.

After a wheat crop has sufficient stored soil water to produce seed, each additional inch of soil water increases the yield potential 5 to 7 bushels per acre. Fall crop residue management for overwinter soil water storage is critical for efficient use of our available precipitation and optimum yields.

Table 1. Overwinter soil water storage after winter wheat with three residue treatments at two Oregon Locations from Aug. 1, 1980 through Feb. 28, 1981 (Ramig, USDA-ARS, Pendleton, OR).

Location and Precipitation

Aug.1-Feb.28

Stubble Treatment Soil Water Storage

Aug.1-Feb.28

(inches)

Storage Efficiency

(%)

Pendleton

11.9 inches

Burned 6.8 57
Flailed 8.7 73
Standing 9.0 76
Moro

7.2 inches

Burned 4.5 62
Flailed 5.7 79
Standing 6.0 83
     
 

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