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;
5. Salt content of manure.
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.
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
|Table 8.1. Input of five manure types needed
to maintain annual mineralization rate of 200 pounds nitrogen
|Annual application rate
|Poultry manure, 1.6%N
0.90, 0.10, 0.075, 0.05
|Fresh bovine waste, 3.5%N
0.75, 0.15, 0.10, 0.075
| Dry corral manure, 2.5%N
0.40, 0.25, 0.06, 0.03
| Dry corral manure, 1.5%N
0.35, 0.15, 0.10, 0.075
|Dry corral manure, 1.0%N
0.20, 0.10, 0.075, 0.05
|Source: Western Fertilizer Handbook,
7th ed., 1985. California Fertilizer Association.
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
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
|After 2 days
|After 4 days
|After 7+ days
|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.
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
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
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.
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
|Table 8.3 The maximum amount of pollutants
that can ever be applied to a given site.
|Cumulative Pollutant Loading Rates
|Source: Arizona Administrative Code, R18-13-1505.
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
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
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.