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Basic Definitions and Assumptions

December 4, 2008

Field Screen:

Field Names
  • No two fields on a farm can have the same name.
  • Can not include any character that is not a letter, number, dash or period. This means no commas, apostrophes, or quotes. This is true for all fertilizer and nutrient source names in Snap-Plus.
  • Are sorted alphabetically by the software, not by numbers. So use 01, 02... instead of 1, 2...
  • Must be the same as the names used on the soil test report for electronic importing soil test data.
Field Slopes and Slope Lengths
Replace the defaults with measured values if you have them. The default slope and slope lengths are from a Natural Resource Conservation Service (NRCS) database. See the NRCS document RUSLE 2 Planning Choices for more information about the correct method for measuring slope and slope length

N restrictions
When a symbol appears in the N restrictions column after a soil mapping unit is selected for an individual field, it indicates that there is a comparatively high risk of nitrates leaching to groundwater from this soil.

Definition of symbols:
  • p - High permeability soils
  • r - Soils with less than 20 inches to bedrock
  • w - Soils with less than 12 inches to apparent water table
  • + - This map unit may have any of the three restrictive features listed above, however an on-site investigation is needed to identify which restrictions may actually be present.
The Nutrient Management Planning Standard 590 places limits on late summer and fall nitrogen applications on these soils. If applications in excess of these limits are applied in Snap-Plus, a warning message will appear in the nutrient application planning window and the application will be in red type on the cropping screen.

Below Field Distance and Slope to Water
These fields are for entering the distance and slope of the flow path or channel for runoff from the lower edge of the field to surface water. This information is used in the P Index for estimating the proportion of the phosphorus running off the field that is likely to be transported to the nearest stream or lake.
  • The ranges are broad because big changes in slope and slope length make relatively small changes in expected P delivery
  • Soil maps are useful to estimate the average slope. The soil mapping units of the land along the drainage pathway between the lower edge of the field and the nearest stream or lake will have a slope designation.
Rotation start year: This is the crop year that Snap-Plus will use as the start of the rotation string for calculating rotational soil loss, P Index, P2O5 and K2O balances. When a field is added, the current planning year will appear here as a default. You can change the start year as you enter field management information on the Cropping Screen or in the Rotation Wizard.

Field notes: This column is for entering information about a field that will be helpful to remember during the planning process. It is a good place to note if the field has winter manure spreading restrictions due to slope or proximity to water.

Nutrient Sources Screen:

Nutrient types and analysis
Default values appear for the first-year available nutrients when a manure species and type is selected in the "Nutrient type" column. These defaults are from Part III of the Companion Technical Document to the NRCS Nutrient Management Standard 590.

If the farm's manure has been analyzed, change the first year available nutrient values by typing the lab report values over the defaults.

Grazing nutrient types represent feces and urine directly excreted by the animal. Grazing animals are assumed to excrete the same amount of nutrients per animal unit as is used in calculating that species' solid and liquid manure nutrients, but the dry matter % of the analysis is adjusted to get a better representation of the dry matter deposited by grazing animals. The manure dry matter application rate is used in RUSLE2 soil loss calculations.

Cropping Screen:

Rotation settings
The rotation length in number of years starting with the year you indicate will be used to indicate the string of crop years included in rotational soil loss, P Index, and P2O5 and K2O balance calculations.

Checking contour will set all tillage and planting operations used in RULSE2 to be on the contour with the relative row grade 10 percent of slope grade.



Crop year
A crop is assigned to the calendar year that it is harvested.

Crop years go from the completion of harvest of the previous crop to harvest of the present crop. The Snap-Plus crop lists includes crop names for "double crops" that describe the crops in a crop year when a second crop is planted after harvest of the first, such as "Winter wheat (forage) to soybeans".

Fall manure and fertilizer applications are assigned to the crop year that the crop they feed is harvested.



Tillage:
Snap-Plus tillage choices are linked to the following specific RUSLE2 basic tillage descriptions for calculating soil loss:
  • Fall Chisel, disked = Fall chisel, twist, disk, fcult
  • Fall Chisel, no disk = Fall chisel, twist, fcult
  • Field Cultivation = fcult
  • Fall MB Plow = Fall moldboard plow; disk, fcult
  • Spring Chisel, disked = Spring chisel, twist, disk, fcult
  • Spring Chisel, no disk = Spring chisel, twist, fcult
  • Spring Cultivation = Sfcult
  • Spring MB Plow = Spring moldboard plow; disk, fcult
  • No Till = No-till
  • Strip-till = Strip Till
Choose the tillage that most closely resembles the practices on a given field. Where there is no exact tillage match available, choose one that includes more passes or disturbs soil more aggressively than the one actually used on the field. That way you will be likely to overestimate soil loss, ensuring that a field meeting T in this Snap-Plus analysis really does meet T.

Manure Applications Spread Method
Unincorporated - Manure remains on surface for three or more days following application
Incorporated - Manure is mixed into the soil by some sort of tillage within three days following application
Injected - No manure is left on the surface following application
Grazing - Manure is applied to the field by direct excretion from the animal

Fertilizer Applications Spread Method
Unincorporated - Fertilizer remains on surface for three or more days following application
Incorporated - Fertilizer is mixed into the soil by tillage following application
Subsurface - Fertilizer is applied below the soil surface, no fertilizer is on the surface following application

Cropping Screen Recommendations and Calculations

Automatic calculations:

Nutrient recommendations
These recommendations are from UWEX A2809 Nutrient Application Guidelines for Field, Vegetable and Fruit Crops in Wisconsin, November, 2006.

Prior years' extra
This is the amount of plant-available P2O5 and K2O applied over UW recommendations summed over the entire crop years since the past soil test. This allows planners to determine how much of the P2O5 and K2O recommended for the current crop were already applied in prior years. When a new soil test is taken, the recommendations are based on the current soil P and K levels which will reflect prior manure and fertilizer applications. Therefore the prior years' extra is reset to 0 whenever a new soil test is used.

Adjusted recommendation
This row contains the P2O5 and K2O recommendations adjusted to account for excess P2O5 and K2O applied in other years.

Total credits and applications
This is the sum of the available nutrients from previous legume crops, previous manure applications (if 2nd and 3rd year manure credits are used), and crop year manure and fertilizer applications. It does not include the prior years' extra discussed above.

Over (+)/Under (-) UW Recommendation
This row shows the amount that total plant available nutrients are less than or greater than UW-Extension recommendations for the current crop. Positive numbers mean more nutrients were available than recommended and negative numbers represent under-applications.

Rotations summaries calculated with "calculate all" button

Average Soil Loss
The rotational soil loss calculations are performed by RUSLE2 (dll version 11/12/2008). Nutrient Management Standard 590 requires that the rotation average soil loss value be less than the Tolerable Soil Loss (T) (shown on the Cropping Screen below Avg. Soil Loss).

P Index
The rotational P Index is an indicator of the amount of phosphorus leaving the field and being transported to surface water in runoff annually on average for the crop years in the rotation. The Phosphorus Index is one of the tools used for phosphorus-based nutrient management planning according to Wisconsin's Nutrient Management Standard 590.

P2O5 and K2O Balances
The nutrient balance summary shows the total amounts of first-year plant-available P2O5 and K2O applied as manure or fertilizer minus total crop removal based on yield over the years specified. Crop removal values come from UWEX Publications A2809. The rotational P2O5 balance is one of the tools used for phosphorus-based nutrient management planning according to Wisconsin's Nutrient Management Standard 590.