Swine Manure as a Fertilizer Source

Table of Contents

Prepared by
J. P. Zublena, Extension Soil Science Specialist; J. C. Barker, Extension Agricultural Engineering Specialist; J. W. Parker, Extension Area Swine Specialist; and C. M. Stanislaw, Extension Swine Specialist

Publication AG-439-4
Revised
June 1993 (MOC)

Last Web Update:
December 1997 (DBL)

Swine manure can be an excellent source of nutrients for crop production. The key to proper management is determining the nutrient content of the manure, the percentages of those nutrients that are available to the plant, and the nutrient requirements of the plant. Considered together, these three factors will help you apply the proper amount.

Nutrient Content of the Manure

Because the nutrient content of swine manure varies among operations and over time, the manure must be analyzed before you apply it to the land. Waste samples, from North Carolina, can be analyzed for $4.00 by contacting the North Carolina Department of Agriculture (NCDA), Agronomic Division , Plant and Waste Analysis Lab, 4300 Reedy Creek Road, Raleigh, NC 27607-6465. Other qualified private laboratories are also available (fees vary).

Samples collected for analysis should be representative of the pit or lagoon. If the waste is to be applied as a slurry, the storage pit or basin should be agitated before sampling. Collect approximately 3/4 of a pint of material in an expandable container, being sure to leave air space.

If you cannot have a sample analyzed, determine the application rate by using the average nutrient values for different swine manure systems shown in Table 1. Table 2 shows the average amounts of secondary and micronutrients present in swine manures. These values can be used as planning guidelines, as long as you realize that they are not as accurate as a sample analysis.

Nutrient Availabilities

The total nutrient content reported on a manure analysis report (or the levels shown in Tables 1 and 2) is not immediately available to the crops when the manure is applied. Some elements are released when the organic matter is decomposed by soil microorganisms. Other elements can combine with soil constituents and be made unavailable. Nitrogen may also be lost to the atmosphere through volatilization or denitrification, depending on the application method and soil moisture levels.

Table 3 lists the proportion of nutrients available for crop use during the first year of application for given application methods. When determining the application rate, refer to the availability coefficient for the appropriate application method, and then multiply that number by the corresponding nutrient value on the waste analysis report (or by the values shown in Tables 1and 2). Waste analysis reports from the NCDA's Agronomic Division show the nutrient availabilities for the first crop.

The most recently applied waste is not the only source of nutrients; they are also available from previous applications of manures or from legumes crops. With the exception of nitrogen, updated soil tests are the best means of determining nutrient reserves from manure applications. Table 4 can be used to estimate available nitrogen carryover from legumes.

Application Rates

Land application rates of manure are generally determined by matching the available nitrogen or phosphorus content of the wastes to the nutrient requirements of the crops. In most cases, nitrogen determines the application rate unless the area is designated "nutrient sensitive" and indicates that phosphorus movement off-site could contaminate surface waters. In areas not designated as nutrient sensitive, phosphorus movement can be adequately controlled with conservation methods that minimize soil and nutrient runoff. The conservation methods include grass field borders, grassed waterways, contour planting, and reduced tillage. Leaching of phosphorus is extremely limited on mineral soils and should not contribute to groundwater contamination.

Nitrogen recommendations for various crops are listed in Table 5. Use these rates as guidelines with the realistic yield capabilities for each crop and field. With feed and forage crops, excessive manure application can produce high nitrate concentrations, which can harm livestock (through nitrate poisoning) and promote nutrient imbalances that may lead to grass tetany. If loading rates are based on phosphorus, apply the amount suggested by soil test recommendations. Other nutrients such as potassium, magnesium, and the micronutrients manganese, zinc, and copper may not be supplied in sufficient quantities for normal crop production. In such cases, apply the supplemental nutrients with a commercial fertilizer as recommended by a current soil test.

In addition to the supply of nutrients, proper soil pH is required to promote organic matter decomposition, improve crop yields, and ensure nutrient availability. The biological conversion of organic matter to nitrate is an acid-forming process that will continue to reduce soil pH unless you follow an adequate sampling and liming program.

To help you determine land application rates, a worksheet is provided at the end of this publication.

Timing of Manure Applications

In addition to carefully calculating the application rate, you must also minimize the delay between applying the manure and planting the crop. Precise timing increases the amount of nitrogen used by the crop and thus reduces leaching. The risk of surface water and groundwater contamination is greater in areas of high rainfall and where manures are applied in the fall or winter for spring crops. On sandy-textured soils, apply manures at low rates throughout the growing season, wherever possible, to reduce nitrogen leaching caused by the soil's low nutrient-holding capacity.

Exercise caution when applying lagoon liquid through irrigation onto standing crops that are undergoing stresses.

Acreage Requirements for New Facilities

Whenever samples of manure or lagoon liquid are available for analysis, the specific results should be used to determine application rates and acreage requirements. However, when you are planning new facilities, average values can help determine the approximate acreage requirements for a given size swine operation. Table 6 can be used to determine the minimum acreage a new unit will need for manure use.

An example will make these methods clear. A producer is interested in starting a 500-sow farrow-to-finish operation using an anaerobic lagoon collection system. The producer is considering spraying the lagoon liquid effluent on bermudagrass being grown for hay. The realistic yield expected for this field is 6 dry tons per acre. How many acres of bermudagrass would be needed?

Using Table 5, the maximum nitrogen (N) rate required is 300 lb per acre (6 tons x 50 lb N/ton). Go now to Table 6 under surface broadcast column 300, and you will find that each sow would require 0.088 acres to utilize its waste. A 500-sow operation would thus require 44 acres (0.088 x 500 = 44).

Value of Manure

To compare the value of manure to commercial fertilizer, convert the manure nutrients to available nutrients by using their availability coefficients. In the example that follows, the amount of available nitrogen (N), phosphorus (P₂O₅), and potassium (K₂O) in each inch of lagoon liquid is approximately 68, 37, and 93 pounds per acre, respectively. At $0.225 per pound of nitrogen, $0.22 per pound of phosphate, and $0.12 per pound of potash, the manure's gross worth is

(68 x $0.225) + (37 x $0.22) + (93 x $0.12)

or

$15.30 + $8.14 + $11.16 = $34.60 per acre for each inch of lagoon liquid.

This value does not include labor or irrigation equipment costs, nor does it include the value of any secondary or micronutrients available in the manure. In addition, it assumes that the soil test has indicated a need for each nutrient, when, in fact, many nutrients may not be needed. Nutrients not needed should not be considered in assessing the financial value of the manure.

Land Application Worksheet

Farmer Jones has a swine operation in which lagoon liquid is applied through a travel gun to fertigate a field for corn. His yield goal is about 120 bushels per acre, and he decides to apply the equivalent of 120 pounds of nitrogen per acre (Table 5). His land is not subject to erosion, nor is it in a nutrient sensitive watershed. The corn crop will be planted in the same field that had soybeans last year. He has grass borders on his field to further reduce the potential of nutrient or pesticide runoff.

Farmer Jones uses a starter fertilizer on his corn crop at a rate to supply 10 pounds of nitrogen per acre and 34 pounds of P₂O₅ per acre. He intends to supply the remainder of nitrogen from liquid swine lagoon effluent. How much effluent does he need to apply to meet the nitrogen needs of his corn crop? How much will be needed to supplement the crop with additional K₂O or P₂O₅ to satisfy his soil test recommendations of 50 pounds of each nutrient per acre? The answers are given in the worksheet.

The authors wish to acknowledge the assistance and cooperation of the North Carolina Department of Agriculture's Agronomic Division in the analysis of samples and the development of the data used in this publication.