Fall 2002
Whole farm nutrient planning
Jeff Lorimor, Department of Agriculture and Biosystems Engineering
If managed correctly, manure is an excellent plant nutrient resource and soil “builder,” resulting in many important environmental benefits. Soils regularly receiving manure require less commercial fertilizer (conserving energy and limited phosphorus reserves); are higher in organic matter, contributing to greater soil productivity; and may experience less runoff and erosion and better moisture conservation. However, an increased risk to water quality results from excess application of manure nutrients to a cropping system. Whole farm nutrient planning asks the question, Do my nutrient inputs equal nutrient outputs? The fundamental concern is whether a livestock or poultry operation is concentrating nutrients.
Single-field nutrient concentration issue. Some fields, often those closest to the livestock facility, receive excessive manure applications, whereas commercial fertilizer is purchased to meet the needs of fields more distant from the livestock. Spreading manure based upon convenience and not the crop’s nutrient requirements concentrates the nutrients in nearby fields or in small areas within a field.
Individual farm nutrient concentration issue. Farms focused primarily on livestock production import significant quantities of nutrients as animal feeds. Livestock use only 10 to 30 percent of these nutrients, excreting the remainder as manure, which can result in a concentration of nutrients on the livestock farm and a shortage of nutrients (typically replaced by purchased commercial fertilizers) on neighboring crop farms that provided the feed for the livestock operation. The net result may be a nutrient imbalance on the crop farm, and an oversupply on the livestock farm.
Regional nutrient distribution issue. Whether considering a cluster of farms, a township, a county, state, or a larger region, the question remains the same: Do nutrient imports equal nutrient exports from the region?” If the answer is no then either nutrients are being concentrated or they are being depleted in the respective area. In livestock-producing regions, more often than not nutrients accumulate because of feed and fertilizer imports.
Nutrient flow. Nutrients arrive on livestock operations as purchased animals, fertilizer, animal feed, nitrogen (N) fixed by legume crops, and nitrates in rain and irrigation water. These “inputs” provide nutrients for crop and livestock production as well as those nutrients that escape into the environment. As mentioned above, livestock use only 10 to 30 percent of the nutrients in livestock feed, excreting the rest as manure. Within the boundaries of the farm, there is a recycling of nutrients between the livestock and crop components. Manure nutrients are recycled, at least in part, for crop production, and feed crop nutrients are recycled as animal feed for livestock or poultry production. Outputs are meat, milk, eggs, crops, and manure. If the unused nutrients in the manure are ignored, and not efficiently used for crop production, a seriously unbalanced condition is initiated in the crop field.
Evaluating a livestock system’s nutrient balance from a whole farm perspective provides a more complete picture of the driving forces behind nutrient-related environmental issues. The original sources of these nutrient inputs are clearly identified, which in turn suggest management strategies for reducing excess nutrient accumulations. The following four management strategies should reduce nutrient imbalances: 1) alternative livestock feeding programs, 2) efficient use of manure nutrients in crop production, 3) marketing of manure nutrients, and 4) manure treatment.
Alternative feeding programs. Opportunities are available for reducing both N and phosphorus (P) inputs by alternative livestock feeding programs. For example, feeding phytase to swine and poultry and reducing the P in their rations can typically reduce P excretion by approximately 30 percent. Feeding dairy cows to National Research Council (NCR) requirements, rather than overfeeding them, can result in significant reductions of manure nutrients. Minimizing protein and phase feeding can reduce manure nitrogen from swine. In addition to changes in feed rations, some additional options that may reduce purchased feed nutrient inputs include 1) alternative crops or crop rotations that result in a greater on-farm production of livestock protein and P requirements, and 2) harvesting and storage practices that improve the quality of animal feed and reduce losses.
Using manure nutrients for crop production. By accurately crediting manure nutrients in a cropping program, the purchases of commercial fertilizer can be reduced or eliminated. Manure contains all the nutrients necessary for crop production, but these nutrients may not be in the proper ratios. Good multiyear nutrient management plans allow full use of the manure nutrients while supplementing with commercial fertilizers to achieve the correct balance. Swine finisher manure applied every other year ahead of corn in a corn–soybean rotation provides all necessary nutrients for both the corn and the following year’s beans.
Marketing of manure nutrients. Once feeding strategies are fine-tuned and a good manure nutrient management plan is in place, if there are still excess nutrients, exporting some manure may be necessary. Additional farmland can be acquired or the manure may be marketed. Marketing of manure creates an additional managed output, similar to the sale of crops or livestock products. Many poultry producers in Iowa have successfully been marketing manure for several years. Marketing manure allows the farm “boundary” to be expanded to achieve a nutrient balance.
Manure treatment. In some situations, producers may consider manure treatment technologies similar to municipal and industrial waste treatment systems. Some manure treatment systems focus on disposal of nutrients with modest environmental impact. For example, treatment systems commonly dispose of wastewater N as N gas (no environmental impact) or ammonia (some environmental impact). This alternative is preferable to N losses to surface or groundwater. Complementary manure treatment and manure marketing strategies can contribute to improved nutrient balance. For example, some producers are successfully combining composting (for odor control and volume reduction) with marketing of manure to crop farms and urban clients.
Indicators of potential whole farm nutrient imbalances. The following points may serve as guidelines to help you determine whether you have a nutrient imbalance on your farm:
- Soil P levels for the majority of fields are increasing with time.
- Soil P levels for the majority of fields are identified as high or very high in a soil test.
- The majority (more than 50 percent) of the protein and P in the ration originates from off-farm sources.
- Livestock feed programs routinely contain higher levels of protein and/or P than NRC or land-grant university recommendations.
- A manure nutrient management plan is not currently used to determine appropriate manure application rates to crops.
- Less than 1 acre of crop land is available per 1,000 lb of live animal weight, and no manure is transported to off-farm users.
Whole farm nutrient planning is not a new concept. Many producers are already doing it by using a good nutrient management plan and carefully controlling rations. It is simply another way to understand the basic relationships between farm imports and exports. If the two do not match, Mother Nature will make them. If imports are low, crop yields and/or animal production decrease. If imports exceed exports, nitrogen may be lost through ammonia volatilization, soil phosphorus increases, and increased phosphorus losses may occur. One way or another, a balance is achieved. Whole farm nutrient planning simply allows the producer to exert more control over what goes where.
Materials contained in this article have been adapted from the Livestock and Poultry Environmental Stewardship Curriculum supported by CSREES, USDA, U.S. EPA, National Agriculture Assistance Center and the University of Nebraska Cooperative Extension Service under Cooperative Agreement Number97-EXCA-3-0642. Copies of the LPES curriculum can be ordered from Midwest Plan Service at https://www.mwpshq.org/catalog.html
