Guide to Adding Pasturing and Grazing Information to NMAN Calculations

Table of Contents

  1. Introduction to grazing units
  2. Where do I enter grazing information in NMAN?
    1. Location 1 - Storage System Information (MSTOR) screen
    2. Location 2 - "Add Grazing" tab
    3. Location 3 - Effect of Grazing Unit Calculations on Overall Field Nutrient Balance
    4. Location 4 - Percentage of Grazing Units Managed
  3. Appendix 1: Grazing calculation and assumption descriptions
  4. Appendix 2: Detailed examples for representing livestock pasturing in NMAN

Introduction to grazing units

Many livestock operations send their animals out to pasture (graze). NMAN can help you take pasturing into account when sizing manure storages and when determining the nutrients applied to fields by pastured animals.

The Ministry of Agriculture, Food and Rural Affairs (OMAFRA) developed the term "grazing unit" in NMAN for this purpose. You may already be familiar with nutrient units (NU). A grazing unit (GU) is the same as an NU, but is used for the portion of time the animals are on pasture. For example, if 10 beef cows with their calves (10 NU) are on pasture 50 per cent of the time, there are five GU.

Note: NMAN assumes an even distribution of manure during grazing. This may not be true, especially if you have large, non-rotated pastures. NMAN may not adequately consider zones of over fertility (i.e. near water sources and shade) and under fertility in the field. You may need to subdivide the field or make other changes if this is an issue. Also, providing supplemental feed in pasture in the same location (e.g. a round bale feeder) can result in a localized buildup of nutrients at this feeding area.

This web page explains how you can use NMAN to develop your nutrient management strategy and plan when your operation includes grazing of animals.

More information on the calculations and that are behind the procedures for characterizing grazing in NMAN is given in Appendix 1. Detailed examples demonstrating the use of grazing units are shown in Appendix 2.

Where do I enter grazing information?

You can enter and/or analyze grazing information in four locations in NMAN. The information below goes through the order you would usually encounter them when completing a typical livestock-based nutrient management strategy or plan that includes grazing.

Location 1 - Storage System Information (MSTOR) Screen

This screen is used to determine the volume of manure produced by livestock and to calculate the manure storage size. Click the "Add Livestock" button on the "Add Storage System" screen. You can enter grazing information in the "Livestock Information" pop-up box.

The "Livestock Information" pop-up box showing grazing information entered and an arrow showing  where the "Manure production changes" box is checked.

Figure 1. Entering grazing information in the "Livestock Information" screen. When you check the "Manure production changes" box (identified by the arrow), you are able to enter start and end dates for each type of manure production.

In the example in Figure 1, the user has indicated that 100 dairy cows will be six months in the barn in winter and six months on pasture during the summer. Check the "Manure production changes throughout the year" box to make these allocations. NMAN assigns approximately 50 per cent of the NU as GU.

Including grazing information in this screen reduces the amount of manure that needs to be stored and used. Entering pasturing information without checking the "Manure production changes throughout the year" (as shown in Figure 1) assumes pasture usage is year round. This may result in too small of a manure storage for winter if your operation only pastures for a specific period of the year. NMAN will add all the GU together if there are more types of grazing livestock involved with this storage system. This total amount of GU "manure" will be displayed in the utilization column located on the right-hand side of the "Storage System Information" screen. You will need to account for the GU in the cropping calculations to show you have a complete nutrient management plan.

Location 2 - "Add Grazing" Tab

You can input grazing information on the "Field Information" screen of your nutrient management strategy and plan worksheet. To access this screen, click on "Farm Unit" in the left-hand column of the Nutrient Management Strategy & Plan worksheet, click the "Add Farm" button and then select the "Add Field" button in the toolbar.

The field screen has a series of tabs that you can use to enter information about a field, such as the soil type and field size. To enter grazing information, click on the "Field Inputs" tab and select the "Add Grazing" tab (see Figure 2). The "Grazing Information" pop-up box will appear when you select this tab (see Figure 3). Four options for grazing types are shown in this box.

Note: NMAN will give a warning and not display the pop-up box if you have not entered a pasture material type for the field in the "Livestock Information" screen described in Location 1.

The "Field Information Screen" with the "Field Inputs Tab" selected and an arrow pointing to the "Add Grazing" tab.

Figure 2. The "Field Information Screen" with the the "Field Inputs Tab" selected. Note the "Add Grazing" tab in the second row of tabs.

The "Grazing Information" pop-up box showing available "Grazing Type" options.

Figure 3. The "Grazing Information" pop-up box showing available "Grazing Type" options. Information such as "Cropping Year" and "Field Size" are filled out automatically using the information you previously entered.

Figure 4 shows the pop-up box with an annual grazing crop selected. NMAN assigns a "Base Carrying Capacity" for this crop of 1.27 GU per acre (GU/ac) (3.1 GU/hectare (ha)) (see assumptions in Appendix 1). (The base carrying capacity is the average amount of grazing units a field will support over a cropping year.) This means it is expected that over a full cropping year period, this grazing crop will, on average, support 1.27 GU/ac. This equals approximately 0.8 dairy cows or 1.3 beef cows per acre (two dairy cows or 2.6 beef cows per hectare).

Grazing Information screen with "Annual Grazing Crop" selected and no "Additional Feed."

Figure 4. Grazing Information screen with "Annual Grazing Crop" selected and no "Additional Feed."

Depending on the information in the "Base Carrying Capacity" and the "Additional Feed" fields, NMAN assigns values for nutrients added onto the field by grazing animals and nutrients added off of the field and calculates a balance. In this case since no additional feed was added, it is a negative balance, indicating that more nutrients were removed than were added.

Note: One GU adds 48 pounds (lb.) (about 22 kilograms (kg)) of nitrogen (N) and 96 lb. (about 44 kg) of P2O5. If no feed is added, the same GU removes 64 lb. (29 kg) of N and 130 lb. (59 kg) of P2O5. This means that there is a net removal of fertility from the field when no feed is added.

NMAN determined that 15.2 GU are managed on this 12 acre (4.9 hectare) field. Since 72 GU need to be managed, additional pasture fields and/or additional feed will be required.

Effect of additional feed

NMAN accounts for the additional feed added to the field (but is limited to a maximum of two GU/ac (about five GU/ha). NMAN recalculates the crop removal balance by taking into account the addition of the feed.

Note: NMAN assumes even application of the nutrients across the field, which can be more challenging with feed additions. One way of addressing this is to use a mobile feeder that is moved around the field.

Figure 5 shows what happens with 30 per cent additional feed entered. In this case, the nutrient balance is positive, showing a buildup of nutrients occurring on the pasture field.

Note: A positive nutrient balance will occur when additional feed input exceeds 25 per cent.

The "Grazing Information" pop-up box with 30 per cent additional feed entered.

Figure 5. The "Grazing Information" pop-up box with 30 per cent additional feed entered. This feed input increases the "Base Carrying Capacity" to 1.81 GU/ac (4.47 GU/ha). The addition of N and P2O5 increases due to more feed, causing a positive overall nutrient balance (buildup).

NMAN will generate a flag when the additional feed exceeds 50 per cent, meaning more information is required. This means the pasture is more like a feed lot so may need to be assessed as such for nutrient management planning purposes.

Ability to Override Information

In NMAN, you can choose to assign all the available GU to the field being described, or to override the base carrying capacity and enter in a value that more closely matches the management practice being followed. In both cases, a flag will be displayed if the base carrying capacity exceeds the default calculations (determined by the grazing type and additional feed inputs) or exceeds two GU/ac (around five GU/ha).

Location 3 - Effect of Grazing Unit Calculations on Overall Field Nutrient Balance

When you close the "Grazing Information" pop-up box, you return to the "Field Inputs" summary screen (as shown in Figure 6). This screen displays the effect of the pasture crop (with 30 per cent additional feed inputs from Figure 5). In this case, NMAN indicates no extra fertilization is required. NMAN shows a slow increase in nutrient buildup in the field (in the crop removal section). There are no red flags indicating the increase is within limits.

Increasing additional feed will raise the amount of nutrients added to the field. At just over 50 per cent additional feed, the buildup will exceed P2O5 limits. Rotating the field into crops to draw down the phosphorus (P) buildup can address this limit (accomplished by changing the planned material application frequency at the bottom of the "Field Inputs" tab).

The "Field Inputs" tab on the "Field Information" summary screen showing the effect of a grazed field with 30 per cent additional feed entered.

Figure 6. The "Field Inputs" tab on the "Field Information" summary screen showing the effect of a grazed field with 30 per cent additional feed entered.

Grazing a field for part of a year

NMAN can show the effect of grazing after a crop. For example, you can add a harvested grain corn crop followed by grazing on corn stover by adding multiple crops on the same landbase in one cropping year.

Location 4 - Percentage of Grazing Units Managed

For your Nutrient Management Strategy or Plan to be complete, the number of GU calculated during the MSTOR calculations should equal or exceed the number of GU used in the fields. The "Nutrient Content & Utilization" section on the "Storage System Information" screen gives this number (Figure 7).

The "Storage System Information" screen showing "Grazing Units Managed" in the "Nutrient Content & Utilization" section.

Figure 7. The "Storage System Information" screen showing "Grazing Units Managed" in the "Nutrient Content & Utilization" section. Since only 30 per cent are managed, additional pasture (or feed) will be required

Using the examples shown in Figures 1 and 5, 100 cows generated 72 GU, and 12 acres (30 ha) used 22 GU. Thirty-one per cent of the GU is managed, as shown in Figure 7. This leaves 50 GU that still need to be managed. Additional pasture land is required and/or a higher percentage of feed needs to be added to the pasture. Alternatively, the time the livestock is grazing could be reduced.

Appendix 1: Grazing calculation and assumption descriptions

The following assumptions are used within the NMAN software and form the basis for completing crop removal nutrient balance calculations for a pasture field:

  • GU values are based on an animal type's annual manure production. A GU, however, is a function of the amount of time an animal is on pasture. For example, if an animal is on pasture for only six months of the year, then only half of the manure generated in a year by that animal type will be deposited on the field. On the other hand, if an animal has access to a pasture or paddock area during the entire calendar year, the GU value would not need to be adjusted as it is based on an annual amount of manure production. NMAN accounts for pasturing duration in the various grazing options.
  • A grazing animal feeding only on the available pasture and depositing all of the manure it generates back onto the pasture will result in a negative nutrient balance. In general, it is assumed that a pastured animal removes 25 per cent of the nutrients it "harvests" through grazing.
  • A Nutrient Unit generates 95 lb. (43 kg) of N and 120 lb. (54.5 kg) of P2O5. For pasture situations, it is assumed that 50 per cent of N and 80 per cent of P2O5 is available. Therefore, a GU has a net pasture fertilizing value of 48 lb. (22 kg) of N and 96 lb. (43.6 kg) of P2O5.
  • A grazing animal feeding on pasture year around and receives 25 per cent of its dietary needs through additional feed sources will deposit as much usable nutrients as it removes from the pasture.
  • N removal per GU = 64 lb. (29 kg) x [1 - (additional feed (%) ÷ 100)]
    • if the additional feed = 0%, then N removed is 64 lb. (29 kg)
    • if the additional feed = 25%, then N removed is 48 lb. (22 kg) (the same amount that is applied)
    • if the feed percentage =100, then N removed is 0
  • P2O5 removal per GU = 130 lb. (59 kg) x [1 - (additional feed (%) ÷ 100)]
    • If feed percentage = 0, then P2O5 removed is 130 lb. (59 kg)
    • If feed percentage = 25, then P2O5 removed is 97 lb. (44 kg) (about the same as applied)
  • Pasture fields where the livestock are receiving additional feed can have additional carrying capacity. This additional carrying capacity is related to the percentage of the animal's diet that is met by the additional feed as:
    • Pasture Field Carrying Capacity = Base Carrying Capacity ÷ [1 - (additional feed (%) ÷ 100)]
      It is assumed that to maintain a viable pasture, the carrying capacity cannot exceed five GU/ha (two GU/ac) regardless of the level of additional feeding.

Appendix 2: Detailed examples for representing livestock pasturing in NMAN

The following sections describe some common ways to represent livestock pasturing situations in NMAN. We provide suggestions that will help you assess how best to represent pasture examples you encounter as you complete various nutrient management strategies and plans.

Pasture Example 1 - A beef cow-calf pasture

Description: A farmer has 25 acres (10 hectares) of land as their "Field 1" that they have kept in pasture (90 per cent grasses, 10 per cent legumes) for many years now. Other than maintaining the field fences and spreading about 150 lb./ac (68 kg) of 6-24-24 fertilizer on the land each fall, the farmer does very little to maintain the pasture. The farmer rents the land to their neighbour, who pastures their herd of 30 beef cows (with calves) during the growing season (May 15 to October 15). No additional feed is brought into the farm. In the fall, the neighbour takes the beef cow herd back to the home farm. The neighbour sells the calves in the fall.

Representing pasture Example 1 in NMAN

Manure production (for a Nutrient Management Strategy):

While the animals are not owned by the owner of pasture field, it is clear that the farm is a generating site. The cow/calf herd is generating manure during the summer months while they are on pasture. While on pasture, the cows would be represented through NMAN's MSTOR screen as follows:

Click on the "Add Livestock" button on the "Storage Information" screen to open up the "Livestock Information" pop-up box. (See Figure 8). Enter in the information for your operation. For Example 1:

  • "Brood Cows (includes calves to Weaning)" is selected as the livestock type.
  • The "Number of Livestock" entered is 30.
  • The manure they produce is entered as a "Pasture Manure" type.
  • The pasture field is used 42 per cent of the time (five out of 12 months).
  • One beef cow (with calf) represents one GU. Multiplying this GU value by the time these animals are placed on pasture results in the estimate of 12.6 GU/year of pasture manure. This is the volume of GU that is produced. The GU need to be applied to the pasture field through the "Add Grazing" button under the "Field Inputs" tab on the "Field Information" screen.
  • There is a yellow flag indicating that not all the manure is managed from these animals. You need to indicate that remaining manure production is covered in the neighbour's nutrient management strategy. You can also click the "Manure production changes throughout the year" box and only enter the pasturing period.
"Livestock Information" pop-up box with arrows pointing to the type and number of livestock and amount of pasture manure entered for Example 1.

Figure 8. "Livestock Information" pop-up box.

Field application (for a Nutrient Management Plan)

Field 1 is a pasture field that receives commercial fertilizer. Therefore, you need to enter both grazing and fertilizer information under the "Field Inputs" tab on the "Field Information" screen.

a) Adding grazing information

From the "Field Information" screen, click the "Add Grazing" button to open the "Grazing Information" pop-up box shown in Figure 9.

Note: You will need to follow the directions above to add pasture material types into your plan. You will not be able to open the "Grazing Information" pop-up box without this information.

The "Grazing Information" pop-up box showing calculations for Example 1.

Figure 9. The grazing information calculations for Example 1.

Enter in the information for your operation. For Example 1:

  • The "Cropping Year" is the cropping year you are planning for.
  • The "Material Type" is the "Perennial Pasture" type that was described on the "Storage Systems Information" screen described above. The volume of material (in GU/year) is displayed here as well.
  • The "Grazing Type" is "Perennial Pasture."
  • "Additional Feed" is zero per cent.
  • The suggested (maximum) base carrying capacity is 0.54 GU/ac. However, farm experience on this site suggests the pasture can only handle about 30 cows with calves over the summer. Click the "Use all grazing units on this field" button; NMAN calculates the actual base carrying capacity by dividing the number of GU by the acreage of the pasture field (12.6 ÷ 25 = 0.50).

The "Nutrient Balance" is a negative number because there are no feed additions.

b) Adding fertilizer information

From the "Field Information" screen, open the "Field Inputs" tab and click on the "Add Fertilizer Application" button. This opens the "Fertilizer Application" pop-up box shown in Figure 10. The fall addition of 150 lb./ac of 6-24-24 fertilizer would be added through this pop-up box, which contributes to the overall nutrient balance for the field.

"Fertilizer Application" pop-up box showing calculations for Example 1.

Figure 10. Fertilizer application calculation for Example 1.

Pasture Example 2 - Beef cattle pastured following first cut of hay

Description: A beef farmer applies 15 tons/ac of solid beef manure to a 20 acre (49 hectare) hay field in the fall, and the following summer cuts the field for first cut hay. The field is made up of 70 per cent grass and 30 per cent legume. After the hay harvest on July 1, the farmer lets about 50 cattle (beef backgrounders) into the field to use as pasture. The cattle were pastured on the surrounding 30 acres starting May 1, but these fields are now starting to be overgrazed. The 20 acre (49 hectare) field is only 40 per cent of the total pasture the cattle pasture on, but because the field has good forage they spend about 60 per cent of their time in that field. Commercial fertilizer is not applied, and no additional feed is brought into the site.

Representing pasture Example 2 in NMAN

Manure production (for a Nutrient Management Strategy)

The cattle are on pasture beginning May 1, and are let onto the 20 acre field after July 1. The cattle are removed from the pasture on October 31. You need to consider May 1 through October 31 when estimating the volume of manure generated on pasture. This period is six months of the year, therefore half of the manure produced by this livestock type in a year needs to be entered as "Pasture Manure," and the other half entered as "Solid Manure" in the "Livestock Information" pop-up box (see Figure 11).

Open the "File Information" tab, found at the top of the AgriSuite screen, and click on "Add MSTOR Worksheet." This allows you to enter in manure storage information for your operation. Click "Add Livestock" to open the "Livestock Information" screen shown in Figure 11.

Livestock Information - General Information

For Example 2:

  • 50 beef backgrounders are selected as the livestock type.
  • 50 per cent of the manure the cattle produce is stored as "Pasture Manure."
  • The cattle are present on the farm and producing manure the entire year, so NMAN calculates utilization at 100 per cent.
  • One beef backgrounder represents 0.33 GU.

The example operation has 8.4 GU of manure to distribute over 50 acres (123.5 ha).

Field application (for a Nutrient Management Plan)

Enter in the field size and soil test information using the "Properties" and "Soil Test" tabs on the "Field Information" screen. The soil sample for the example: Phosphorus = 10 and Potassium = 50. Next, enter the cropping information. The example field did not receive pastured animals until after a cut of hay was harvested. Under the "Field Inputs" tab, click the "Add Crop or Cropping Year" button to open the "Cropping Information" pop-up box (see Figure 12). The "Crop" type is "Pasture cut for hay," and "30% legume 70% grass." Planting and harvest dates are not applicable.

The "Cropping Information" pop-up box for Example 2.

Figure 12. The "Cropping Information" screen for Example 3.

Next, you need to describe the grazing activity for the field. Under the "Field Inputs" tab, click on the "Add Grazing" button to open the "Grazing Information" pop-up box (Figure 13).

  • The "Cropping Year" is the cropping year you are planning for.
  • The "Material Type" is the "Pasture" type that was described on the "Livestock Information" screen. The volume of material (in GU/year) is displayed here as well.
  • The Grazing Type is "Pasture Following 1st Cut Hay."
  • Additional Feed is zero per cent.
  • The suggested (maximum) carrying capacity is 1.0 GU/ac. However, the actual carrying capacity is only 0.17 GU/ac (8.4 GU/year/50 acres) of pasture land for six months means on average 8.4 ÷ 6 = 1.4 GU/month deposited on the fields. This field only has pastured animals for four months of the year. Therefore, 1.4 x 4 = 5.6 GU. During those months, the cattle are only on the field 60 per cent of the time, so 0.6 x 5.6 = 3.36 GU applied to the field. Since there are 20 acres in this field that was first cut for hay, the actual carrying capacity is 3.36 ÷ 20 = 0.17 GU/ac. Click the "Override Base Carrying Capacity" button to enter this value of 0.17 as the actual carrying capacity of the field. This will ensure that the "Field Size" and "Grazing units" match what is happening in the field. Note that with this example, only a fraction of the pasture manure generated is applied to this field. The remainder would need to be applied to the other 30 acres of permanent pasture associated with this operation.
  • The "Nutrient Balance" from the grazing activity is negative.

The "Grazing Information" pop-up box for Example 2.

Figure 13. The "Grazing Information" window for Example 3.

With all of the manure applications to this field entered, you can check the Nutrient Balance section in the "Field Inputs" tab for red flags. There are no flags in this example.


For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca
Author: OMAFRA Staff
Creation Date: 22 July 2015
Last Reviewed: 22 July 2015