April 15, 2004
High Plains farmers expect adequate moisture as they prepare to plant 2004 crops, according to officials with the High Plains Underground Water Conservation District No. 1 and the United States Department of Agriculture — Natural Resources Conservation Service (USDA-NRCS).
“We conducted our pre-plant soil moisture survey in late January. Since then, general rainfall has occurred across the region. As of mid-March, most areas within the High Plains Water District have already received 50 percent or more of their total 2003 rainfall,” said Scott Orr, conservation technology division director. The district serves 15-counties in the High Plains.
As irrigators prepare for planting, they should check soil moisture in specific fields to decide if they need pre-plant irrigation. An illustrated step-by-step procedure to assess soil moisture conditions is found in the water district's Water Management Note: Estimating Soil Moisture By Feel and Appearance.
When irrigation capacities cannot keep up with seasonal peak water demand, producers sometimes rely on stored soil moisture to help meet the demand.
“Crops grown in this area get most of their water from the top three feet of soil when available. Producers should concentrate on the moisture content within this zone to (determine) if the zone is at the target 75 percent of capacity, or if irrigation is required. The remaining 25 percent would allow room for precipitation, thus not exceeding a soil's storage capacity. Water applied in excess of a soil's storage capacity can move below the crop's effective root zone,” said Orr.
He added that irrigation applications focused on establishing moisture for in-season use should be planned with these conditions in mind. Investment return, pumping capacity, and irrigation system efficiencies should also be considered before any irrigation management strategies occur.
High Plains Water District and USDA-NRCS personnel visited soil moisture monitoring sites maintained by both agencies. Neutron moisture meters were used to gather data at six-inch intervals throughout the upper five feet of soil. The agencies produce maps that provide information to producers about moisture stored in the soil profile (available moisture) and moisture the soil can still hold for plant use (deficit moisture). The pre-plant soil moisture information includes January moisture, but not any February or March precipitation.
On the maps, a “cross hair” represents soil moisture monitoring sites within the county. The number in the upper left side of the cross hair indicates the soil moisture (in inches) found in the upper three feet of the soil. The number in the lower left side of the cross hair represents the soil moisture (in inches) in the upper five feet of soil. The letters in the upper right side of the cross hair show the crop grown at that site in 2003. The letters in the lower right side of the cross hair show the type of irrigation system (if any) used at the site last year.
As an example, a soil moisture monitoring site may have a 2.3 in the upper left corner; a 3.5 in the lower left corner; “CT” in the upper right corner; and “PV” in the lower right corner. This shows that the site had a 2.3-inch moisture deficit in the zero to three-foot portion of the soil and a 3.5-inch deficit in the zero to five-foot portion of the soil. Cotton (CT) was grown at the site and received supplemental irrigation from a center pivot (PV) during the 2003 growing season.
The soil moisture availability and deficit maps were published in the March issue of The Cross Section, the water district's monthly newsletter.
The High Plains Water District and the USDA-NRCS remind producers to preserve existing soil moisture conditions by reducing any tillage operations that might expose moist soil to evaporation from sunlight and wind. The agencies also encourage producers to prepare their fields to maximize the benefits of timely rainfall. Use of furrow dikes, contour farming, conservation tillage, and circular row patterns under pivots are practices producers can use to reduce water runoff from their fields.
For more soil moisture information or to request a copy of The Cross Section or the water management note, contact the High Plains Underground Water Conservation District No. 1, 2930 Avenue Q, Lubbock, Texas 79411-2499, or call (806) 762-0181. Additional soil moisture information is available on-line at www.hpwd.com
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