See below for more details on the nutrient management entry boxes in COMET-Farm.

Users may add fertilizer, manure, compost, and biochar applications in the Nutrient Management activity data section. The total nitrogen (lbs/ac) applied to the crop will be calculated at the top of the panel when fertilizer and/or organic amendment events are added. 


Fertilizer Applications

To include fertilizer application(s) as a part of management, select +Add Fertilizer Application. Users will be prompted to select the date of their application, as well as their fertilizer type from a dropdown menu (see list below). Once a value is entered for either Total Amount Applied or Total N Applied, the other value will update by default - and vice versa - based on the selected fertilizer type. For instance, if a user selects Urea Ammonium Nitrate (30-0-0) and enters 11 lbs of N applied, COMET will default the Total Amount Applied to 34.38 lbs/ac. 


DayCent cannot support multiple fertilizer events on the same day. To accommodate for this limitation, users can either:

  • Enter sequential dates for each fertilizer type. For example, if two fertilizer events occurred on May 15th, enter one event on May 15 and one event on May 14.

  • Sum the total amount of nitrogen applied across fertilizer events and add it as one singular event on one day


The total amount of nitrogen being applied to the system is the most important variable included in the model, so if a certain fertilizer type is not included in the tool, users may select “Element-N” and adjust the input values until the desired amount of nitrogen is applied to the system.


Fertilizer types include:

  • Ammonium Nitrate (34-0-0)
  • Ammonium Nitrate Phosphate (23-23-00)
  • Ammonium Nitrate Phosphate (27-14-00)
  • Ammonium Phosphate Sulphate (16-20-00)
  • Ammonium Polyphosphate Solution (10-34-00)
  • Ammonium Sulphate (21-00-00)
  • Ammonium Thiosulphate Solution (12-00-00)
  • Ammonium nitrate sulfate (26-30% N)
  • Anhydrous Ammonia (gas) (82-00-00)
  • Aqua ammonia (20-00-00) (solution)
  • Calcium Ammonium Nitrate 
  • Calcium Nitrate
  • Diammonium Phosphate (18-46-00)
  • Element-N (N)
  • Element-S (S)
  • Mixed Blends
  • Monoammonium Phosphate (11-55-00)
  • Monoammonium Phosphate (12-51-00)
  • Potassium Nitrate
  • Sodium nitrate (16%)
  • Sulfur Coated Urea
  • Urea (46-00-00)
  • Urea Ammonium Nitrate (28-00-00)
  • Urea Ammonium Nitrate (30-00-00)
  • Urea Ammonium Nitrate (32-00-00)
  • Urea Ammonium Phosphate (27-27-00)
  • Urea Ammonium Phosphate (34-17-00)
  • Urea formaldehyde (38%)


Organic Amendment Additions

To add organic amendment application(s), click +Add Organic Amendment. Users will be prompted to enter information on their application date, select their manure type from a dropdown menu, and provide a value for fresh weight applied (lb/ac). Fresh weight applied can be entered as it is applied (wet or dry mass); slurry amounts are entered in increments of 1,000 gal/acre, and manure is entered as solid and organic fertilizers are entered as tons/acre. Default values will populate for moisture (%), nitrogen content (%), and C/N ratio (lbs N/ac), but users can edit these values if desired. Please review an amendment lab analysis if the parameters are unknown. 

Organic Amendment Table Input

Description

Date

When the manure/compost is applied.

Amendment Type

Selection of common amendment types (manures, slurries, compost). When users select a type from the dropdown, COMET will default N%, C:N, and moisture % from the NRCS manure management handbook. Users may edit any defaults COMET provides. If an amendment is unavailable, please select “other manure” and enter the required details. 

Moisture %

Moisture percentage of the fresh weight applied. 

Nitrogen Content (%)

Percent Nitrogen content. Slurry analyses often present Lbs N/1000 gal instead of N%. Example 15.19 lbs N/1000 gal to %N content conversion:


Average dairy slurry weight = 8.5lb/gal



    15.19 lbs N       x   1 gal slurry      =

1000 gal slurry          8.5 lbs slurry


   15.19 lbs N      =   0.00179 Lbs N  x 100 = 0.179% N

8500 lbs slurry             1lb slurry

C:N Ratio

Ratio of total carbon to total nitrogen


This section uses a mass balance approach to ensure that total percentages of different portions do not exceed 100%. If users modify the default values to exceed 100%, they will get the following error message: The data entered indicates the fractions of carbon, nitrogen, phosphorus, and water exceed 100% for this event. Please check the test report or product label and adjust the percentages to correct this issue. 


Example: a grower applies 10,000 gallons of dairy slurry on their field. The lab report indicates the slurry is 92% water, 0.13% nitrogen, and 0.06% P, with a C:N ratio of 7.7. A C:N ratio of 7.7 indicates that the carbon fraction is: 0.13 (from the nitrogen) x 7.7 = 1.001%. The remaining fraction (approx. ~6.8%) comprises potassium, calcium, hydrogen, and oxygen bound to carbon in the organic matter, and other trace materials. 


Click here to view a sample soil analysis report, where each parameter asked for in COMET-Farm is indicated with a red asterisk.


Organic amendment types include:

  • Alfalfa Meal
  • Beef Manure-Solid
  • Beef Slurry
  • Blood-Dried
  • Bone Meal
  • Chicken-Broiler (litter) Solid
  • Chicken-Broiler Slurry
  • Chicken - Layer Slurry
  • Chicken - Layer Solid
  • Compost or Composted Manure-Solid
  • Dairy Manure-Solid
  • Dairy Slurry
  • Farmyard Manure Solid
  • Feather Meal
  • Fish Emulsion
  • Fish Scrap
  • Guano
  • Horse Manure-Solid
  • Other Manure-Solid
  • Sheep Manure-Solid
  • Soybean Meal
  • Swine Manure-Slurry
  • Swine Manure-Solid


Biochar Amendment Additions

Biochar amendments are a new addition to COMET-Farm in 2024. Click Add Biochar Amendment to include biochar in the field’s management practices. Users will be asked to enter the amount applied (ton/ac), the molar ratio of H to organic carbon content C (must be a value between 0.15 and 0.7), the feedstock type (manure, wood, herbaceous biomass, rice residue, biosolids, or nut shells, pits, and stones), and the production technology (pyrolysis or gasification). More information on biochar amendments can be found on page 3-34 of the USDA methods document.