Using irrigated winter wheat to balance crop water use
By Gary Stone and Gary H. Hergert
UNL Panhandle Research and Extension Center
What a challenging year for irrigators. It has been difficult keeping up with irrigation. Pivots have certainly helped and furrow irrigation has been a major challenge. The reservoir system has enough water to get irrigators through this season, but what about next year, 2013, and beyond?
Producers who are under pumping allocations may have already used up water they "banked" in previous years. They will not have that water to fall back on next season. If the region receives the same amount of snowfall as last year, expect major problems with crop water management. Pathfinder Reservoir is about 50 percent of capacity, probably enough to supply irrigation needs for 2013. Some rationing or allocations may take place in 2013 to get us through to 2014 if we do not get a good snow pack.
Many producers plant winter wheat as a cover crop after dry bean harvest to reduce wind erosion and trap snowfall for moisture. If irrigation water in reservoirs will be in short supply and pumping allocation reserves have been used up, irrigators will not have the same amount to use next year. Consider that irrigated winter wheat cover crop as a crop for grain harvest.
Winter wheat would require about 18 inches of evapotranspiration. Depending on soil moisture left form the dry bean crop, a pre-irrigation in the fall to provide good soil moisture to an 18-inch depth would be ideal. In "normal" years rainfall, research in the Panhandle shows that about 7 to 8 inches of irrigation will produce maximum yield. In dry years, 11 to 12 inches of irrigation is required, whereas in wetter years 5 to 6 inches is sufficient.
Water use for corn is 24 to 26 inches, fully irrigated alfalfa requires 28 to 32 inches and dry beans require about 16 inches of irrigation.
Irrigated winter wheat offers a number of options. First, it spreads a grower's risk. It would be harvested sooner; and compared to corn and dry beans crop water use would be lower and earlier in the season.
Second, irrigated winter wheat can be harvested for grain and the straw baled for forage. Read more about this option at UNL Extension in the Panhandle's website: http://panhandle.unl.edu/web/panhandlerec/Panhandle_agecon_1.
Or the crop could be green chopped or swathed and baled as forage. If the irrigated winter wheat is taken off early enough, there is the potential for planting another forage crop back in the stubble: sorghum sudan grass, foxtail millet or an oat mixture for a second crop. Depending on rainfall, this second crop would probably require at least an additional 4 to 6 inches of irrigation.
Fertilizer management for the winter wheat crop should include soil testing after dry beans. Growers should apply adequate phosphorus in the fall to promote rooting. Nitrogen rates can be in the range of 25 to 30 pounds N per acre with additional nitrogen being applied before boot stage the following spring, depending on stand, winter survival and yield potential.
If the decision is not to take the irrigated winter wheat to grain yield, or to harvest it for forage or spray out, nutrient carry-over can vary, depending on the stage of growth at cutting or spraying. Removal of the crop as hay will remove most of the nutrients and additional N and possibly some P will be required for the next crop. If you spray it and leave as a cover crop, the nutrients in that crop will not be released until the residue decomposes and returns to the soil nutrient cycle, so normal fertilization of the next crop would be required.
Producers have the flexibility to watch the futures market of all of the crops over the winter and also see how the reservoirs' water supply develops before deciding what to do in the spring. More information on winter wheat production can be found at these UNL Cropwatch websites:
--Soil Management to Optimize Winter Wheat Production, cropwatch.unl.edu/web/wheat/soils; and
--Wheat Production Systems, Nebraska, http://cropwatch.unl.edu/web/wheat/production.