Utilization of Dairy Manure as Fertilizer
Prepared by:
James C. Barker, Professor and Extension Specialist
Biological and
Agricultural Engineering
North Carolina State University, Raleigh, NC
Published by: North Carolina Cooperative Extension
Service
Publication Number: EBAE 133-88
Last Electronic Revision: March 1996 (JWM)
Significant amounts of N, P, and K and lesser amounts of trace elements are
present in dairy manure and wastewater. Decomposition and mineralization of
the manure in soil releases these nutrients for crop growth. Land
application of manures should become an integral part of an overall soil
fertility-agronomic program. Manure application rates to cropland or
grassland should not exceed the crop nutrient requirements. In addition,
timing of application, regular manure analysis and soil testing, liming and
supplemental fertilizer needs should be considered. Fortunately, these same
practices which utilize the fertilizer value of manure also help to reduce
nutrient losses in runoff, thereby, resulting in water quality benefits.
COLLECTION AND STORAGE
In 1988, North Carolina dairy production generated about 300 million gallons
of recoverable manure, lagoon liquid and sludge consisting of 2,800 tons of
plant available N, 2,200 tons of P2O5, and 3,200 tons of K2O plus
micronutrients representing about 4 million dollars worth of plant nutrients.
Dairy manure accumulation and nutrient concentrations can be influenced by
several factors. Waste from open housing systems and manure storage areas is
diluted by rainfall. The longer manure remains in the housing or storage
area prior to removal, the more chance there is for ammonia nitrogen loss.
Daily Spread or Temporary Storage
Probably the least expensive dairy manure handling system in terms of initial
investment for small to moderate size herds is lot scraping either directly
into a spreader for daily field spreading or into a short-term (30- to 90-day)
storage or stacking area. This method has some disadvantages, however,
from a manure utilization standpoint. Since spreading has to occur
frequently, manure cannot always be soil incorporated, therefore, nitrogen is
lost from the field surface. Also during wet weather conditions, manure
either cannot be spread in the desired fields or else the soil structure is
damaged from driving equipment through muddy conditions.
Earthen Storage Basin
One of the more popular recent methods of dairy
manure handling has been earthen liquid storage basins for 6-12 month manure
accumulations. In addition to the convenience of only having to spread
manure once or twice a year, the nutrients are better utilized. Manure can
be spread in the spring on corn silage land or in the fall on small grains at
times when it can be soil incorporated either by direct injection or disking.
A disadvantage is the relatively high equipment costs and the competition for
spreading time in the spring. Custom applicators operate in some areas of
the state with manure mixing, pumping and spreading costs about $10 per 1000
gallons.
Table 1. Dairy Manure Characteristics
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Manure N P2O5 K2O
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tons/cow/year lbs/ton
------------------------------------
Lot scraped manure 17.0 9.9 6.2 8.7
11.1 - 24.8 3.0 - 20.1 0.6 - 13.3 2.3 - 20.0
gallons/cow/year lbs/1000 gallons
------------------------------------
Liquid manure slurry 7750 22.5 14.0 21.1
3560 - 19900 8.4 - 49.7 0.2 - 37.5 0.7 - 50.1
acre-inches/cow/year lbs/acre-inch
------------------------------------
Anaerobic lagoon liquid 0.34 137 77 195
17 - 268 10 - 233 13 - 571
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MANURE CHARACTERISTICS
Sampling and Analysis
Table 1 gives an average and range of dairy manure
characteristics. Note the variability. Because nutrient values do vary
considerably with time, dairymen are strongly encouraged to have a sample of
manure analyzed prior to each major spreading event. The N.C. Department of
Agriculture Plant Analysis Lab, Blue Ridge Road Center, Raleigh, NC 27611;
phone: (919)733-2655, analyzes manure and wastewater samples for primary
nutrients and trace elements for $4 per sample. Representative samples of
the manure should be taken from several locations in the waste storage and
mixed together in a plastic bucket. About 3/4 pint should be placed in a
nonmetallic flexible container, refrigerated or iced if possible, and
delivered to the lab as soon after collection as possible.
It is very difficult to get a representative sample from a liquid manure
storage basin until the manure has been thoroughly agitated into a slurry.
Dairymen with liquid manure systems are encouraged to take samples for
analysis after agitation even though the results will not return from the lab
until after the manure has been spread. This still gives a record of the
amount of nutrients that have been applied and whether or not supplemental
fertilizer is needed. Begin to develop a running record of the manure
analyses results specific to an individual farm and use the average of these
results to calculate the next manure application rate.
LAND APPLICATION
Nutrient Availability
All of the nutrients applied in dairy manure are not
available to the crop. As much as 75% of the ammonia nitrogen in manure can
be lost to the atmosphere by leaving manure exposed on the field surface for
one month or longer. No more than 25% is likely to be lost if the manure is
soil incorporated within 48 hours and only 5% will be lost by direct
injection.
The remaining ammonia nitrogen can be utilized directly by crops but the rest
of the manure nitrogen in organic form must first be mineralized by soil
bacteria to ammonia before the crop can utilize it. This is a slow process
with only about one-half of the organic nitrogen becoming available to the
crop during the year of application. Taking these factors into account,
availability coefficients (Table 2) can be used to estimate the crop
available portion of the total nitrogen shown on the lab analysis report.
Table 2. Dairy Manure Nitrogen First-Year
Availability Coefficients
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Injection Disking Surface
in 48 Hrs Spread
__________________________________________________
% of total N available to crop
Lot scraped - 57% 43%
manure - (0.6) (0.4)
Liquid manure 68% 60% 44%
slurry (0.7) (0.6) (0.4)
Anaerobic 79% 73% 47%
lagoon liquid (0.8) (0.7) (0.5)
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Scheduling
Timing of manure applications should be as close as possible
to periods of maximum plant uptake of N. Fall applications can result in
nitrate leaching losses ranging from 5% of total N applied to clay soils to
upwards of 10% in sandy soils. Fall denitrification N losses range from none
in sandy soils to 35% on clay or poorly drained soils. About 70-80% of total
manure phosphorus and potassium become crop available. In the example, the
15,000 gallon per acre rate would also supply 156 lbs P2O5 and 236 lbs K2O
per acre to the corn silage crop.
Soil Properties
Land application of dairy manure can beneficially alter soil
properties. Overall soil tilth is improved by the addition of organic
matter. The soil infiltration rate, particularly in fine- textured soils, is
increased by incorporation of manure. Increased infiltration also reduces
the soil erosion potential. Dairy manure stimulates plant growth by
increasing the soil water holding capacity. On sandy soils, organic matter
reduces leaching and increases crop yields by helping plants better utilize
water and nutrients.
SUMMARY
Applied to soils in proper amounts, dairy manure improves soil fertility and
crop yields. Carelessly handled, it impairs soil productivity, degrades
surface and groundwater quality, and causes nuisance complaints. An
agronomic plan for manure consists of manure and soil analyses; application
rates; time and method of land application; and the effects of manure on soil
properties, crop yields, and surface and groundwaters. A soil testing
program should be utilized as a guide for supplemental fertilizer and liming
needs, to determine whether salinity problems exist, or whether certain
elements are beginning to approach plant toxicity levels. Nitrogen
recommendations should be based on the manure analysis, crop needs, and
method and timing of application. If enough land is available, phosphorus
and potassium recommendations should be based on soil test results reflecting
any accumulation from past applications.
Example: Rate of liquid manure slurry with the following nutrient analysis
and disked (soil incorporated) into corn silage land needed to
supply 200 lbs available N/acre.
WASTE ANALYSIS REPORT
WASTE ADVISORY SECTION
NCDA Agronomic Division
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LABORATORY RESULTS, percentage of liquid volume
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N - % P - % K - %
0.27 0.07 0.21
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Total N: 0.27 x 83.5 = 22.5 lbs/1000 gallons
Available N: 22.5 x 0.60 = 13.5 lbs/1000 gallons
Available P2O5:0.07 x 2.29 x 83.5 x 0.75 r = 10.5 lbs/1000 gallons
Available K2O: 0.21 x 1.20 x 83.5 x 0.75 = 15.8 lbs/1000 gallons
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NUTRIENTS AVAILABLE FOR FIRST CROP, lbs/1000 gallons
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Application Nitrogen P2O5 K2O
Method
Soil Incorp. 13.50 10.48 15.81
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Application rate: 200 lbs N/ac / 13.5 lbs N/1000 gallons = 14,800
gallons/acre/year
Distributed in furtherance of the Acts of Congress of May 8 and June 30,
1914. Employment and program opportunities are offered to all people
regardless of race, color, national origin, sex, age, or disability. North
Carolina State University, North Carolina A&T State University, U.S.
Department of Agriculture, and local governments cooperating.
EBAE 133-88
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