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Irrigation water management – water optimizer,
crop residue management,
deficit irrigation and soil water management tools
Posted May 30, 2013
By Gary Stone, UNL Extension Educator;
Jessica Johnson, UNL Ag Economist Asst. Extension Educator;
Dr. Gary Hergert, UNL Soil and Nutrient Management Specialist
The 2013 water outlook for the North Platte Valley, the Panhandle and eastern Wyoming does not look good. The area is still in a severe to exceptional drought, and the predicted surface-water irrigation supply may be in the 50- to 60-day range. Groundwater users continue to be under allocations and in a few cases may have exceeded their pumping amounts.
With all of this uncertainty, what are producers to do? There are a number of tools available for producers and urban home owners to help manage water resources.
One tool a producer can use is Water Optimizer, a Microsoft Excel-based program that can estimate a profit-maximizing cropping mix based on a limited amount of water. The Water Optimizer program has four “models” to calculate a cropping mix: single-field, single-year; single-year, multi-field; multi-year, multi-field; and an independent budget calculator to estimate production costs.
Each model seeks to maximize the average net return based on the producer’s estimated water supply and crop production preferences.
This tool has several options that allow users to customize the model to reflect their farm. Water Optimizer asks for information such as soil type, well / pump specifications, preferred nitrogen levels, production costs and anticipated market price for commodities. Through these selections producers can compare a variety of commodity mixes.
The Water Optimizer downloads can be found at this link: http://agecon.unl.edu/wateroptimizer/download.html
We suggest starting with the single-field single-year model first, as it is the simplest form of the program. Be sure to download the Operator Manual for the model you select. For additional help with crop budgets or Water Optimizer use, contact Jessica Johnson or Gary Stone at the Panhandle Research and Extension Center. The main number is 308-632-1230.
Producers who have already selected a cropping mix should consider no-till or limited tillage operations as part of their water management this season. Every producer has their own soil and water management strategies, but consider this:
- Depending on soil type and soil moisture content, each tillage pass could potentially remove 0.5 to 0.75 inch of moisture from the profile.
- Having adequate crop residue will help trap off-season precipitation (such as snow).
- Having adequate crop residue on the soil surface can help reduce soil moisture surface evaporation by 2 to 4 inches during the growing season.
- Having adequate crop residue on the soil surface will help reduce soil erosion from wind and precipitation, and increase water infiltration into the soil instead or running off the field.
- Control weeds that germinate after harvest. Unmanaged weeds can use up stored soil moisture in a hurry.
These management practices can leave more water in the soil for the crop to utilize. In some instances a tillage operation will be necessary for seedbed preparation or weed management. Consider strip-tillage for planting operations in order to leave the crop residue in place.
For producers who have limited amounts of water, another tool to consider is deficit irrigation, a strategy where the producer utilizes stored soil moisture and in-season precipitation to get the crop established and through vegetative stages. Then the producer applies the majority of their irrigation water during the reproductive and grain fill stages of the crop.
In most cases, the producer will have to stress the crop during the vegetative stages and apply minimal amounts of irrigation water to keep the crop growing. The producer will be applying less water than is required to meet the full ET (evapotranspiration) of the crop. This strategy will have a reduction in yield when compared to full irrigation. However, deficit irrigation will encourage grain fill rather than vegetative growth.
Other water management tools are soil-water sensors and ET gauges. Soil water sensors are placed in the field of the growing crop at different depths relative to the root zone of the crop. The producer takes readings from the sensors every two to four days to determine how much soil moisture is available for the crop and how much irrigation is needed to fill the soil profile.
ET gauges, also called atmometers, are instruments that simulate the evapotranspiration of an alfalfa crop. Readings from ET gauges are taken weekly, and used to estimate the crop water use for that week based on the given crop and crop growth stage. The producer can then know how much irrigation water to apply to each field to replace the water used by the crop.
There are also a number of grass ET gauges that simulate actively growing grass so the home owner can track their lawns’ water use.
There will be follow-up articles on the soil water sensors and ET gauges in the near future.
More information is available on-line from UNL Extension at droughtresources.unl.edu.