Calculation Of Manure Application Rates

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Depending on the type of manure and how it is stored and applied, the nitrogen and phosphorus in manure may supply crop needs for an entire growing season. In addition to these nutrients, manure contains potash, several trace elements and large amounts of organic matter. Organic matter from manure can increase the organic matter content of the soil which can improve the water holding capacity, aeration, infiltration, soil tilth, biological quality and resistance to erosion.

Like any fertilizer, a proper application rate must be calculated to ensure optimum agronomic and economic benefit. This information is calculated using manure analysis information and should be monitored by soil testing where manure has been applied.

Nutrient Availability
Nutrients in manure exist in two forms: organic and inorganic. Since only inorganic forms of nitrogen and phosphorus are available to plants, only a portion of the total nutrients can be utilized in the year of application. The organic forms must first be converted to an inorganic form (mineralized) which occurs naturally in the soil. This can be advantageous for the crop because not all of the nutrients from manure are immediately available. The slow release of nutrients minimizes possible crop damage and prevents excess nutrients from being lost before plant uptake occurs.

Availability of manure nutrients to the crop depends on the organic/inorganic makeup of the manure. Approximately 50% of the total phosphorus in manure is in the organic form, with only a small portion available to plants in the year of application. The remaining 50% of the total phosphorus is inorganic phosphorus, similar to commercial fertilizer. In general, 50% of the total phosphorus in manure is available to plants in the first year. To ensure enough phosphorus is available to a growing crop, add 12-15 lbs/ac of P2O5 as a starter fertilizer with the seed. Check the fertilizer recommendations of specific crops for any seed placed fertilizer restrictions.

With nitrogen, three different measurements are given in a manure analysis:

  • Total Kjeldahl Nitrogen (TKN) is the total amount of organic and ammonia nitrogen in the sample.
  • Ammonia nitrogen (NH3) is the amount of inorganic nitrogen that is readily converted to plant available forms.
  • Organic nitrogen is determined by the difference between total nitrogen and ammonia nitrogen.

The general rule of thumb for nitrogen mineralization from manure is to expect 25-30% of the organic nitrogen to be available to plants in the first year, with the remainder becoming available during the next three years at a decreasing rate. Soil testing should be conducted to confirm the actual amount of available nitrogen in any specific situation. When considering application rates of manure based on nitrogen content, consider the amount of readily available nitrogen (ammonia) relative to the amount of gradually available organic nitrogen. In some cases, it may be necessary to add a starter fertilizer to ensure the crop has enough nutrients available during its early growth stages.

Volatilization of ammonia represents a significant means of nitrogen loss. Loss of ammonia depends upon method of application and time prior to incorporation, as shown below:

Method of Application

% N Loss (incorporation within 3 days)

*broadcast, no incorp. 25-35
broadcast, immediate incorp. 15-25
broadcast, no incorp. on established forage 35
injection 0-2
*irrigation 25-35
*If time to incorporation is greater than three days, nitrogen losses can be 40-60% for broadcasting and 60-80% for irrigation.

Application Methods
There are many variations of application techniques for manure. Application methods are evaluated based on cost, level of soil disturbance, level of nutrient loss, and odour.

Application Method



Broadcasting applications
   -without incorporation

relatively inexpensive
results in considerable odour production; intensive field traffic with manure spreaders results in soil compaction; nutrient loss due to ammonia volatilization and runoff
   -with incorporation incorporate as soon as possible to reduce nutrient losses and minimize odour
Irrigation can be applied over wet soil conditions; relatively inexpensive; should be incorporated immediately nutrient losses and odour production are higher than with other application methods
Direct injection of manure into the soil nutrients directly placed in root zone; results in little or no nutrient loss and minimal odour production; may be accomplished using a liquid manure spreader equipped with a cultivator-type injection unit or pumped directly from a storage facility to a field up to two miles away using pipes and hoses connected to an injector equipped with sweep openers these types of injectors result in high soil disturbance, making them unacceptable units in perennial forage or zero tillage fields; cost, time, fuel and labour are limiting factors

Overall Strategy
To have an effective manure management strategy, all of the following considerations must be integrated into a program that accounts for the nutrients in manure and manages the nutrients to satisfy crop needs.

  • manure analysis - field and laboratory methods of analysis are available. Field test kits allow for immediate analysis of nitrogen content and should be checked against a laboratory analysis first. Manure analysis from a given operation should change very little from year to year if there are no major changes in feed ration or manure storage. Manure from sampling lagoons may vary greatly if not thoroughly agitated, since solids usually settle out during storage.

  • sufficient land base - do you own enough land close by or do pre-arrangements need to be made with a neighbor?

  • soil test - according to Farm Practices Guidelines.

  • methods of application - if not applying manure by direct injection, incorporate manure as soon as possible to avoid losses due to runoff and volatilization losses and to reduce odour.

  • time of application - apply as close to planting as possible to minimize risk of nutrients lost to runoff, volatilization, leaching, etc. (Winter manure application is not recommended because a large amount of the manure may be lost as runoff and poses risks to surface water pollution).

  • calculate application rate - based on nutrient that will be present in the soil in the largest quantity (nitrogen or phosphorus). Once a fertilizer application rate has been calculated, determine the size of land base needed to apply the available manure at the calculated rate.

    The following tables serve as guidelines to calculate an application rate for manure. Keep in mind the principle of fertilizing according to crop needs and the nitrate guidelines for soil.

A. Moisture Use & Root Penetration

Crop Annual Water Use (in.) Root Penetration (ft.)
alfalfa 20 14
sainfoin 16 11
Russian wild ryegrass 13 7
tall wheatgrass 12 7
sweetclover 11 7
barley & wheat 7 4

B. How Much Manure Nitrogen to Apply - General Guidelines


N (lb/ac)
alfalfa 225
grasses 150
alfalfa-grass mixtures 175
annual crops:
   -medium to heavy soils
   -light soils
Note to points 6A and 6B:
These are not absolute values; there is a trade-off between over- and under-fertilizing with manure. Over-fertilizing to meet or slightly surpass crop nitrogen requirements so that no additional fertilizer need be applied is valid, but excess nitrate in the soil must be closely monitored. Under-fertilizing requires multiple fertilizer applications, which increases costs and the risk of excess nitrates in the soil from a subsequent application. A general recommendation would be to fertilize as close to crop requirements as possible, so that few nitrates are present only in close proximity to the soil surface after the growing season.
  • calibrate equipment - make sure the application equipment is applying manure at the target rate.

  • uniform application

  • keep plans and records

Treat livestock manure as a fertilizer. Once its nutrient content is determined, manure can be managed to benefit crop production with minimal risk to soil and groundwater contamination. The two key managmement points to remember are:

  • Soil Test

  • Manure Analysis

Sample Application Rate Calculation Based on Manure Analysis:

A liquid hog manure sample is analyzed to have 27.3 lb/1000 gal of TKN, 19.7 lb/1000 gal of ammonia and 8.1 lb/1000 gal of phoshorus. Based on soil test and crop requirements, the producer wishes to apply at a rate that meets all of his nitrogen requirements, which is 90 lbs/ac. Phosphate requirements are 25 lb/ac. The manure is to be broadcast in the spring followed by incorporation one day later.


  • 15% volatilization loss (see above)

  • 30% organic nitrogen available in 1st year

  • 50% (approx.) total phosphorus available in 1st year

Calculation Worksheet - Example

Step 1. Soil Test Data
Field ID: SE quarter
Nutrient Target Rate(lb/ac to add)
Nitrogen 90
Phosphate 25
Step 2. Data from Manure Analysis
Nutrients Units (lb/1000 gal or kg/1000L):
Total Nitrogen (A) 27.3
Ammonia (B) 19.7
Organic Nitrogen (A-B) 7.6 (C)
Phosphorous (D) 8.1
Phosphate (D×2.3) 18.6 (E)
Step 3. Amount of manure nitrogen available to crop
Volatilization losses due to application equipment 15% (F)
Organic nitrogen available in first year (C×0.3) 2.3 (G)
Ammonia available (B×[100-F]%) 16.7 (H)
Total Nitrogen available in growing season (G+H) 19.0 (I)
Step 4. Application rate based on nitrogen requirements

Nitrogen Target Rate ÷ (I) = Application Rate (J)
 90 lb/ac ÷ 19.0 lb × 1000 gal = 4737 gal/ac  ----> apply 4500-5000 gal/ac


Step 5. Amount of manure phosphate available to crop
Phosphorus availability factor 50% (K)
Total available phosphate (E×K) 9.3 (L)
Compare (L) with Phosphate Target Rate:
9.3 lb/1000 gal  ----> 46.5 lb/4600 gal;
46.5 lb/ac ÷ 25 lb/ac = 1.9 × (acceptable)

Calculation Worksheet

Step 1. Soil Test Data
Field ID:               
Nutrient Target Rate(lb/ac to add)
Step 2. Data from Manure Analysis
Nutrients Units (lb/1000 gal or kg/1000L):
Total Nitrogen (A)
Ammonia (B)
Organic Nitrogen (A-B) (C)     
Phosphorous (D)
Phosphate (D×2.3) (E)     
Step 3. Amount of manure nitrogen available to crop
Volatilization losses due to application equipment % (F)     
Organic nitrogen available in first year (C×0.3) (G)     
Ammonia available (B×[100-F]%) (H)     
Total Nitrogen available in growing season (G+H) (I)      
Step 4. Application rate based on nitrogen requirements
Nitrogen Target Rate ÷ (I) = Application Rate (J)


Step 5. Amount of manure phosphate available to crop
Phosphorus availability factor 50%           (K)    
Total available phosphate (E×K)        (L)    
Compare (L) with Phosphate Target Rate: 
  • if (L) is less than the target rate: add a starter phosphate fertilizer
  • if (L) is greater than the target rate: do not exceed the target rate by more than 2.5×; otherwise, calculate an application rate based on phosphate instead of nitrogen (switch steps 3 and 5).






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