December 16, 2004 | General

Using Compost To Reduce Irrigation Costs

BioCycle December 2004, Vol. 45, No. 12, p. 33
Field trials in Illinois examine cost savings from using on-farm generated compost and fewer irrigation cycles to grow crops.
Duane Friend

THE number of on-farm composting facilities in the Midwest has steadily increased over the last five to ten years. Several livestock producers in Illinois – particularly those near urban areas in the central and northern parts of the state – have initiated projects utilizing livestock waste and yard materials. Finished compost usually is applied to crop fields operated by these producers.
Overall, soils in the upper Midwest are excellent for growing agricultural crops. High inherent fertility and water retention allow this area to grow corn, soybeans and other commodities with high yield potential. However, there are pockets of poorer soils present. For example, several areas in Illinois are mostly sand, such as in Mason County, located in the center of the state. Soils in this area have very low water holding capabilities, but are also over an immense shallow aquifer. The majority of acreage in the county is irrigated by center pivot irrigation systems. This area, sometimes referred to as the “Imperial Valley” of the Midwest, grows a variety of crops, including field corn, soybeans, snap beans, potatoes, popcorn, pumpkins, watermelons and cantaloupe.
As energy costs spiral upward, the costs of irrigation increases as well. This situation led University of Illinois Extension staff to pose the following question: If there is a potential for decreasing the number of irrigation cycles needed to grow a crop by incorporating compost, would it pay?
Research conducted at the University of Wisconsin provided insights on the effects of compost application on plant available water. The research examined short and intermediate term use of paper mill residuals and composted residuals in sandy soils in central Wisconsin. Amendments were applied at the rates of 10 to 20 dry tons/acre; plots were planted in a rotation of potatoes and snap beans. Following the second application of amendments, amended plots increased plant available water by five to 45 percent compared to no amendment. This reduced the average amount of irrigation water needed by ten to 90 percent – a potential for reducing the number of irrigation cycles by two to seven.
To determine the potential cost savings of reducing irrigation needs, a program from Kansas State University was employed. This program allows one to input the size of the irrigation system, how much water is applied per cycle, how many feet the water has to be lifted, and the type of energy used – electric, propane, diesel or natural gas.
Using current (fall 2004) energy prices for central Illinois, adding one inch of water for a standard 130-acre system would cost from $160 (electric) to $347 (diesel or propane). If the number of irrigation cycles could be reduced by two to seven cycles per season, the potential cost savings would range from $320 to over $2,400/year on a 130-acre system, depending on the number of cycles reduced and the energy source.
Compost/Irrigation Study
Though results from research may be applied to other areas, many producers like to see research under local conditions. This is particularly true for producers in Mason County, which has soils and groundwater conditions relatively unique to the state. To address this need, a multiyear study was initiated to examine using compost on irrigated cropland in the county.
A number of cooperators, including University of Illinois Extension, Illinois State University, the Mason County Irrigated Growers Association, the Mason County Farm Bureau, and the Mason County Soil and Water Conservation District have participated in the study. Partial funding was supplied through the Illinois Department of Agriculture Sustainable Agriculture Grant Program.
The study utilizes nine subplots. Three of the plots receive 20 wet tons/acre of compost annually (moisture content estimated between 40 and 50 percent). Three more receive 10 wet tons/acre, and the other three receive no compost. Application began in 2002. Compost is supplied by Illinois State University, which has a composting facility at its research farm. It is made from a combination of hog and some cow manure and yard trimmings (mostly fall leaves) from the city of Normal. Popcorn or soybeans are grown in rotation, and normal tillage, herbicide, and irrigation scheduling have been used.
As expected, annual soil testing has shown a significant increase in cation exchange capacity (the ability of soil to hold nutrients) in plots where the highest rates of compost were applied. Organic matter contents also appear to have increased, although the increase is not yet statistically significant.
Average relative soil water content has been checked weekly during the growing season. A reading of 100 percent means that the soil is at field capacity, or holding as much plant available water as possible. Again, at the 20 wet tons/acre rate, the relative water content appears to have increased slightly, but not yet enough to be statistically significant. It was apparent that in some weeks irrigation needed to be more frequent, as some readings produced very low or even negative readings. In theory, this should have made the plots with compost, which contained a little more water, a better growing environment. Yield results to date, which may have increased slightly in the compost-amended plots, are not yet statistically significant.
A variable that may be offsetting the effect of compost is field slope, which is about two percent. Moisture readings, and yields, are consistently higher on the lower end of this slope. It may take several more compost applications before this variable is not an overriding factor. Another factor in play is the amount of compost being used. Higher initial rates of application would likely have been beneficial. Researchers applied compost at a wet ton rate due to a misinterpretation of an Illinois Environmental Protection Agency regulation. Next year, application rates of 10 and 20 dry tons/acre (acceptable under Illinois EPA guidelines for agronomic application) will be used instead of wet ton rates. This will essentially double the amount of compost being applied.
If producers are already composting, there may be potential for cost savings from reducing irrigation cycles. For the best effect, higher rates of application would be needed – i.e., 20 dry tons/acre would be better than 10. A farm making 4,000 to 6,000 dry tons/year of compost could supply enough compost for 200 to 300 acres/year.
Obviously there would be a cost for producing and applying the compost, but if someone were already composting, the costs would already be a part of the operation. However, an irrigator examining costs and benefits associated with starting and operating a composting facility may want to include the potential for reducing irrigation needs in the decision making process.
Buying the compost from an outside source and applying it would likely not be worth the cost savings from reduced irrigation alone. Other benefits from adding compost as a soil amendment would need to be included in the cost/benefit analysis.
Duane Friend is an Extension Educator with University of Illinois Extension in Springfield.
SAMPLES of soil from Mason County, Illinois – along with compost – were used in lab tests performed with the assistance of Extension Specialists at the University of Illinois. The study used various percent mixtures of soil and compost, and examined the water holding content of each mixture. Using gravimetric methods, water content was determined for two levels of water content – field capacity and the wilting point. Field capacity is the point where the greatest amount of plant available water is present. Wilting point is the point where roots of plants cannot extract any more water from the soil. Water may still be present, but it is held tightly too soil and organic particles, making it unavailable for plant use.
Results of the testing suggest that any addition of compost will increase water retention in this type of soil, essentially doubling the volume of water retained. Partially offsetting this increase, however, is the amount of water that would be held below the wilting point, making a portion of this water unavailable for plant use.
A series of articles in BioCycle by Richard Stehouwer provided a comprehensive over of soils, with information on the effects of adding organic materials such as compost. Part II of the article series, “Soil Quality Fundamentals – Water and Air Essentials” (November 2003), includes a discussion about water movement, storage and availability. Copies of the article series are available through the BioCycle archives (, “article archives”).

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