Utilization of Compost Made from Agricultural and Forestry Wastes for Improving the Economic and Ecological Sustainability of Agronomic Crop Production on Low Organic Matter Soils in the San Luis Valley of Colorado
The main objective of this study is to improve water conservation and sustainability of crop production on low organic matter soils in the San Luis Valley, Colorado. This will be accomplished through on-farm demonstrations that will examine the impact field incorporated compost made from agricultural and forestry wastes has on: 1.) reducing the use of synthetic fertilizers and fungicides, by improving nutrient retention in the root zone and the health and diversity of the soil’s biomass, 2.) improving the water utilization, thereby reducing water and power use in center-pivot irrigation systems, 3.) crop yields and production costs for potatoes, barley and alfalfa.
The main objective of this study is to improve water conservation and sustainability of crop production on the low organic matter soils of the San Luis Valley, Colorado. This will be accomplished through on-farm demonstrations that will examine the impact field incorporated compost made from agricultural and forestry wastes has on: 1.) reducing the use of synthetic fertilizers and fungicides, by improving nutrient retention in the root zone and the health and diversity of the soil’s biomass, 2.) improving water utilization, thereby reducing water and power use in center-pivot irrigation systems, 3.) crop yields and costs of production for potatoes, barley and alfalfa.
1. Develop local end markets for agricultural and forestry wastes. Improve the sustainability of potato, barley and alfalfa crop production in the San Luis Valley. Demonstrate the impact that field incorporation of compost has on production
a. The change in the diversity of the soil’s microbiology and biomass.
b. Variations in disease levels in the crops.
c. The potential improvement in nutrient retention in the root zone.
d. The potential reduction in the use of synthetic fertilizers and pesticides.
e. The potential improvement in water utilization and associated reduction in water and electrical power use by center-pivot irrigation systems.
f. The net economic value of compost applications.
2. Dissemination of results to farmers in the San Luis Valley to demonstrate the economic and ecological value of using compost to the long term sustainability of their operations.
Anticipated Schedule for Achieving Objectives
Baseline soil samples were taken in late summer, 2000 and analyzed to establish the nutrient level and microbial levels at each test site. A water sample was taken from each of the center pivot systems and analyzed prior to compost applications. Compost will be applied in the fall of each year of the project. The normal farming practice of the area is to do field preparation in the fall for planting the following spring. In one of the fields, however, it is more practical to apply the compost in the spring for the 2nd year of study due to wind erosion during the fall and winter. During the growing season disease levels, crop health, water utilization and nutrient uptake will be measured. Three cuttings of alfalfa will be harvested for yield during each growing year. Crop yield data will be collected at the end of each growing season for potato and barley crops. All data collected will be summarized at the end of each growing season. In Year 2 and Year 3, summary bulletins will be published in print and on the Colorado State University Website (http://www.colostate.edu/Depts/SLVRC/disease/2001PotatoDiseaseResearchReports.htm). Field days at each site will be held in year two and three during the growing season. A summary of results will be reported each year at potato and grain grower conferences in the San Luis Valley.
Compost was spread at the rates of 0, 4, 8, and 12 tons/acre to two alfalfa and four potato/barley sites in the fall of 2000. During the growing season of 2001, treatment blocks were marked out at each of the six sites. Samples of the compost being applied were collected and analyzed for nutrient content. Three weather stations and 30 tensiometers were set out to measure water content and water holding ability in the soil. Soil samples were taken in April 2001 and 2002, before the growing season, and in October of 2001 and 2002, after the growing season, for each of the four treatments at each site. These samples were analyzed to determine the biodiversity of the soil prior to the introduction of compost. Soil moisture readings were taken every ½ hour throughout the 2001 and 2002 growing seasons to determine if the water holding capacity of the soil was affected by the compost.
Disease readings were taken at all four potato sites throughout the 2001 growing season and readings were taken at 2 of the potato sites throughout the 2002 growing season. One set of readings was taken on plant vigor, number of stems, number of stolons, and percent of stems and stolons with Rhizoctonia. In 2001 and 2002, readings were taken at each potato site measuring the severity of foliar early blight during the latter part of the growing season.
Three alfalfa cuttings were taken during the 2001 and 2002 growing season to obtain yield data at each of the alfalfa sites. Alfalfa samples were analyzed to determine moisture content. Yields at each potato site were taken at harvest in 2001 and 2002. A post harvest analysis was conducted to determine the severity of Rhizoctonia black scurf. Ten tubers/treatment/replication were evaluated.
Compost was spread at the rate of 0, 4, 8, and 12 tons/acre at both alfalfa sites and at two of the potato/barley sites in November of 2001 and 2002. Compost was spread at the two remaining potato/barley sites in April and November of 2002.
Handouts were distributed at the San Luis Valley Research Center’s 2001 Field Day in August, 2001 with an outline and background information on the composting project. A short summary was given on the project. An article, “Commercial composting digs in”, was also published in Ag Journal (Vol. 54, no. 37. Nov. 16, 2001. Arkansas Valley Journal) which discussed the progress of the project, what remains to be done, and the potential benefits of using compost in agricultural situations.
During 2002 a full issue of the CSU potato newsletter, Pomme de terre, Information for Colorado Potato Growers (Vol. 8, no. 1, January 2002) was devoted to a report on the compost project. In addition, field data from the compost project was included in our annual comprehensive research report to the Colorado potato industry.
There were no significant differences in biomass or microbial diversity among the treated sites. Likewise, there was no significant difference in the amount of disease in the potato crop across the four potato/barley sites. The nutrient retention of the soil and the potential reduction in the use of fertilizers and pesticides is yet to be determined. Changes in soil water retention and long term net changes in crop yields also remains to be fully determined. Nevertheless, there appears to be a trend towards lower potato yields among plots that received the high rate (12 tons/A) of compost.
Impacts and Contributions/Outcomes
Two agricultural waste streams, sawdust and cull potatoes, being generated in the San Luis Valley have become problematic for their local industries. Logs harvested from the National Forests surrounding the San Luis Valley are milled locally, generating sawdust for which there are very few feasible uses. In a 1997 Colorado State University (CSU) survey of western Colorado mill operators, the second most mentioned problem was that of mill residues (sawdust). Most of this sawdust has been stockpiled at locations near the mills. Potatoes are the area’s most economically important crop, and the foundation of the local economy. On average, about 9.6% of each year’s potato crop is not marketable, due to size, appearance or presence of disease.
These cull potatoes have become particularly problematic, since the devastating disease, late blight (Phytophthora infestans), has occured in the San Luis Valley, requiring an increase in fungicides used as protection against this disease. This is an additional economic burden to growers and adds a negative burden to the environment. Late blight spores from infested cull piles can be transported by wind to infect the new growing crop, repeating the disease cycle. Research conducted in Maine has demonstrated that properly managed, hot aerobic composting of cull potatoes with sawdust will destroy disease pathogens (including P. infestans) and produce an excellent soil conditioner. Each ton of fresh compost contains 12 lbs of nitrogen, 4 lbs of phosphorus, 9 lbs of potash, 18 lbs of calcium and about 400 lbs of organic matter.
The sustainability of most soils used for crop production in the San Luis Valley would be improved by the addition of compost. Soils in the San Luis Valley used to produce agronomic crops are sandy and extremely low in organic matter (less than 0.5% OM). The water table in many areas of the valley is quite shallow, 5 to 30 feet below the surface. This creates the potential for nutrients applied to the crops to be leached through the soil to the water table, resulting in the loss of nutrients and contamination of the ground water. Addition of organic matter through incorporation of compost would help to improve the soil structure and its nutrient and water holding capacity, reducing the potential for nutrient leaching and improving water conservation. Sawdust and cull potatoes are produced in the San Luis Valley on a fairly consistent basis, in close proximity to one another, and in quantities complimentary to what is needed for hot aerobic composting using the basic Maine recipe and methodology.
While making the compost is logistically possible, there is no established open-end market for the compost, and the San Luis Valley’s isolated location makes it cost prohibitive to ship to more distant markets. Local growers are reluctant to purchase and apply compost because they are trying to minimize production costs after several years of receiving low market prices and they fear that they may be introducing disease into their crop through the compost. The long-term productivity gains that can be realized by improving soils with compost are not yet recognized.
The impact of this project will be assessed in several ways. The quantity of compost applied to San Luis Valley cropland will be monitored annually. The number acres that have compost applied to them will be recorded. Growers using compost will be surveyed to assess changes in water and fertilizer utilization. Volumes of waste sawdust and cull potatoes that are transformed into compost will be monitored. Stockpiles of sawdust will be reduced. Disposal of waste potatoes will become less of a burden on the industry.
Soil Scientist, Associate Professor
Colorado State University Cooperative Extension
C06 Plant Science Bldg.
Ft. Collins, CO 80523-1170
Office Phone: 9704911913
Integrated Weed Managment Specialist
Colorado State University
115 Weed Research Lab
Ft. Collins, CO 80523
Office Phone: 9704913489
Agricultural & Business Management Economist
Colorado State University Cooperative Extension
2764 Compass Dr., Suite 236
Grand Junction, CO 81506
Office Phone: 9702459149