By D. Bruce Bosley

Extension Agent/Cropping Systems

Colorado State University Cooperative Extension

Colorado

It takes warm weather to grow corn and, for that matter, tomatoes, peppers and melons. Therefore, we all ought to be happy with the warming and drying weather, right? A patient person takes whatever nature provides and makes the best of it. But who's that patient? The June "Colorado Water Supply Conditions Update" report, provided by the state Engineer's office has the good news that helps bring patience.

In brief, the report claims that South Platte basin water supplies were slightly above normal at the end of May. Reservoir storage, the major component in the South Platte basin, was 108 percent of normal. Cumulative storage in the major plains reservoirs: Julesberg, North Sterling and Prewitt, was at 94 percent of capacity and cumulative storage in the major upper-basin reservoirs was at 85 percent of capacity.

High surface flows and moderately wet conditions in May significantly helped irrigators as they did not have to use reservoir supplies to "irrigate up" their crops. Further, the report suggests that most basin water users will have a reasonably adequate supply year. The adequacy of the river supply has been significantly enhanced because we have good rains in June allowing irrigation districts to save their reservoir supplies, and allowing additional recharge.

The only caution in the South Platte basin report was regarding administrative management concerns. Many well users remain curtailed as they do not have adequate long-term resources available to develop permanent plans to augment the out-of-priority depletions from their wells.

Farm water conservation measures are still important. Some corn growers have asked whether they should be irrigating corn now or delaying irrigations until the soil bank has had a chance to be depleted to a safe level. Colorado State Extension recommends that, when practical, growers promote deep corn root development during the vegetative growth stage by allowing some midday moisture stress on the crop. Corn fields that wilt during the middle portion of the day (11 a.m. to 3:30 p.m. or so) but recover in the evenings are only mildly stressed. Furthermore, moderate stresses at this stage do not reduce the crop's yield potential.

Studies in corn have shown that once the crop has reached the six leaf stage of growth until one to two leaves prior to tasseling, moderate mid-day moisture stress can contribute to critical stress stage resilience during pollination and early grainfill by developing a deeper rooting profile.

The ability to replenish and maintain soil water reserves must be taken into consideration when making a management decision to allow some crop stress at this time. Withholding water now may lead to trouble on fields where the pumping capacity is limited or where soils take in water slowly and have high runoff. High residue farming practices, such as no-till can help store and save soil water. Raising drop nozzles on sprinklers and slowing them down can also be effective to improve storage and enhancing infiltration. These practices are especially important under center pivot irrigation where it's more difficult to soak deeply than with flood irrigation.

Please contact Bruce Bosley if you have questions (522-3200, ext: 285).

Date: 6/21/05

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