Manure Use and Management


"The application of nitrogen fertilizer shall be limited to that amount necessary to meet projected crop plant needs." This statement is the first Best Management Practice (BMP) listed for managing nitrogen fertilizer use in Arizona agriculture. One of the Guidance Practices (GPs) that can be used to meet this BMP is GP 1.3: "Apply organic wastes to cropland."

When applied to cropland, animal manure can supply nitrogen and other nutrients necessary for plant growth. Arizona's soils are naturally low in organic matter. The use of animal manure on cropland can increase the tilth, aeration, water-and nutrient-holding capacities, infiltration rate, organic matter content, and microbial activity of soil.

Careful consideration of the following factors will help you successfully apply animal manure to your cropland:

1. Nutrient content of the organic wastes;

2. Rate of mineralization;

3. Weed seeds in manure;

4. Method of application and timing of incorporation; and

5. Salt content of manure.

Nutrient Content of the Organic Wastes

The amount of nitrogen found in animal manure depends upon the age and type of animal, feeding rate, type of ration, and how the waste was stored and handled both before and after being applied to the soil. To determine the amount of nitrogen applied, a farm operator must know both the amount of waste applied and its nitrogen content. A laboratory can analyze the manure for total nitrogen content, and the amount of waste applied can be determined by using a calibrated application system.

Rate of Mineralization

Before nitrogen and other nutrients in manure can be used by plants, soil microbes must break them down into forms that are readily available to plants. This process is called "mineralization."

The rate of mineralization is called a "decay series." Different types of waste will have different rates of decay. A decay series estimates the percentage of mineralization that will occur in the years following a manure application. For example, a decay series of 0.35, 0.15, 0.10, 0.075 means that following a dry corral manure application, 35% of the nitrogen is mineralized the first year, 15% of the residual (that which was not previously mineralized) is released in the second year, 10% in the third year, and so on. If the nitrogen concentration of a waste material and its decay series are known, the amount of waste needed each year to supply a constant amount of nitrogen can be calculated. Table 8.1 lists the approximate application rates of five waste materials needed to maintain an annual mineralization rate of 200 pounds nitrogen per acre.

Table 8.1. Input of five manure types needed to maintain annual mineralization rate of 200 pounds nitrogen per acre.
Material and
Decay Series
Pounds of
Annual application rate
1 2 3 4 5
Poultry manure, 1.6%N
0.90, 0.10, 0.075, 0.05
32 6.9 6.2 5.7 5.4 5.5
Fresh bovine waste, 3.5%N
0.75, 0.15, 0.10, 0.075
70 3.8 3.0 2.7 2.5 2.4
Dry corral manure, 2.5%N
0.40, 0.25, 0.06, 0.03
50 10.0 3.8 6.2 4.8 5.8
Dry corral manure, 1.5%N
0.35, 0.15, 0.10, 0.075
30 19.0 10.9 9.0 8.0 10.8
Dry corral manure, 1.0%N
0.20, 0.10, 0.075, 0.05
20 50.0 25.0 18.8 18.5 27.5
Source: Western Fertilizer Handbook, 7th ed., 1985. California Fertilizer Association.

Weed Seeds

Manures can contain seeds from weeds that can prove difficult to control. Because heat generated in manure stockpiles decreases the viability of weed seeds that may be present, the use of well-aged manures instead of freshly excreted materials will help reduce the likelihood of weed infestations from manure applications. Careful attention to the origin and quality of animal feedstuffs may also help reduce the severity of manure-transmitted weed problems.

Method of Application and Timing of Incorporation

Animal manures and wastes should be injected or uniformly broadcast on cropland at recommended rates and then incorporated into the soil as soon as possible. Plowing or rototilling of the soil following surface applications of manure is recommended. Subsurface injection of fluid materials generally does not need additional tillage operations.

Immediate mixing with the soil will greatly reduce odor, nitrogen losses due to ammonia volatilization, and the potential for groundwater and surface water contamination resulting from runoff. Table 8.2 shows the effect of an increasing time lag between surface application and incorporation of animal manure.

Table 8.2 The effect of time lag between surface application and incorporation of poultry and other manures on the percentage of manure nitrogen available to crop plants.
Time of incorporation Percentage of manure nitrogen available
Poultry Other
Immediate 75 50
After 2 days 45 35
After 4 days 30 30
After 7+ days 15 20
Source: Field Application of Manure, 1986. Pennsylvania Department of Environmental Resources.
Note: The information found in this fact sheet was excerpted from Nitrogen Fertilizer Management in Arizona, May 1991. University of Arizona Cooperative Extension.

Salt Content

Manures from concentrated animal feeding operations are usually high in salt content. Most dairy and feedlot manures contain 5 to 10% salt (50,000 to 100,000 ppm). Frequent and/or large (20 tons per acre) applications of manure to cropland increases the risk of salt injury to plants. Salt-sensitive plants such as lettuce, tree fruits and nuts are especially susceptible. The following management practices are recommended for applying animal manures to cropland:

1. Use well-aged manures rather than fresh manures taken directly from feedlots;

2. Apply up to 5 tons per acre of dry matter per year or 10 tons per acre every other year;

3. Use supplemental nitrogen fertilizers only as required based on tissue tests, plant performance and previous experience;

4. Plow or rototill manure into the soil, irrigate and wait at least 30 days before planting;

5. Do not apply manure where water penetration is poor; and

6. Monitor soil salinity and sodium levels by periodic soil tests.

Agricultural Application of Biosolids

Biosolids are another type of organic waste that can be applied to cropland. The following guidelines are recommended for applying biosolids:

1. Make sure that the soil pH is above 6.5 at the time of application to minimize leachability of trace metals and their uptake by plants;

2. Observe the cumulative loading limits for soil applications (Table 8.3). No more than the specified total amount of each pollutant may be applied to a given site in perpetuity;

3. Use crops which exclude heavy metals from the entire plant or from harvested plant parts (e.g., grain, seed or fruit crops);

4. Use sound soil management practices to reduce runoff and erosion; and

5. Monitor toxic element applications and accumulation in soil and plant tissue using periodic laboratory tests.

Table 8.3 The maximum amount of pollutants that can ever be applied to a given site.
Cumulative Pollutant Loading Rates (dry weight)
  pounds/acre kilograms/hectare
Arsenic 36.6 41.0
Cadmium 34.8 39.0
Copper 1,339.3 1,500.0
Lead 267.9 300.0
Mercury 15.2 17.0
Nickel 375.0 420.0
Selenium 89.3 100.0
Zinc 2,500.0 2,800.0
Source: Arizona Administrative Code, R18-13-1505.

Regulations for the application of Biosolids in Arizona

The application of biosolids to cropland is also regulated by law but with a different set of requirements than for animal manure application. The following list highlights regulations relating to the application of biosolids that are not exceptional quality to cropland. For further information as well as permit requirements, please contact the Arizona Department of Environmental Quality (ADEQ).

Permit: Applicators must file a "Request for Registration" form with ADEQ prior to receiving biosolids.

Proximity to wells: Biosolids cannot be stored or applied closer than 1,000 feet from a public or semipublic drinking water well and no closer than 250 feet from any other water well.

Application site: Biosolids should be applied to soil with a pH of 6.5 or greater. The site should have a slope of less than 6% and be at least 32.8 feet from surface water.

Depth to groundwater: This depends on the pathogen reduction class of the biosolids. For Class B biosolids, the minimum depth to groundwater is 10 feet; 40 feet if soil is gravel or coarse to medium sand. For Class A biosolids, the minimum depth to groundwater is 5 feet.

How biosolids are applied: Biosolids cannot be applied at an application rate greater than the agronomic rate of the crop.

If the biosolids are "exceptional quality" biosolids, as defined by state law, then the above requirements do not need to be met.

Because the information here does not cover all legal requirements for the application of biosolids, you must contact ADEQ for more information.

According to state law, anyone who knowingly or negligently violates any requirement pertaining to land application of biosolids, is guilty of a Class 2 misdemeanor and may be imprisoned for up to 45 months per violation.

Acronyms and selected definitions

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