SnapPlus indicates when you have exceeded the nitrogen application rate allowed by the Nutrient Management Standard 590 by highlighting the manure and/or fertilizer applications for that year in red. If an explanation was entered for the non-compliant applications, the cell will be blue. 

When manure and/or fertilizer applications totaling more than the allowable N rate are entered in the Nutrient Application Planner box, an overapplication message will appear in the gray box at the bottom of the nutrient planner screen when the Apply button is clicked. You will also get an error message if you misapply N to soils with N restrictions due to their leaching potential. When an overapplication-of-N message appears, the total N applications to that field should be reduced by at least the amount indicated in the message. If it is not possible to reduce the application, then an explanation for the overapplication should be entered into the Nutrient Application Planner box labeled "Please explain non-compliant applications".

Avoiding Excessive Nitrogen Applications in SnapPlus

This section describes the maximum N application rates allowed under the 590 Nutrient Management Standard for different crops and nutrient sources. Exceeding these rates will cause warning notices to appear in SnapPlus.

There are three types of N excess warning notices:

1.On the cropping screen, the N application cell for This year’s manure or This year’s fertilizer turns red.

2.An overapplication warning message appears in the Nutrient Application Planner screen when you add nutrient applications.

3. The overapplication message will also be printed in the Compliance Check report for the field and crop year with the overapplication.

Note: If the entire plant-available N in a crop year is from legume credits and/or 2nd and 3rd year manure credits, SnapPlus will not generate an excess N message because these N sources are not from current-year applications.

Also note that planners are expected to prepare plans using real, achievable, and preferably calibrated, manure application rates. In order to allow planners to use achievable rates that match recommendations as closely as possible, the warning notices will not appear if the N application rate is just a few pounds over the allowed N for corn and other non-legume crops. Warning flags are triggered once an application reaches 10 lb over the allowance.

The maximum allowable rates of N application for all soils are described for different crops in the following sections:

•Corn

•Wheat

•Legumes

•Crops other than corn, wheat or legumes

There are additional restrictions on spring, summer, and fall N application rates on soils that have a high leaching potential, and these are described in the section Avoiding excess spring, summer, and fall N applications on soils with a high nitrate leaching potential.

Corn maximum N application rates

Because the UW Extension MRTN recommended rate for corn can vary from year-to-year, depending on corn and N prices, the maximum allowable N rate for corn is set at the high end of the range for the 0.05 N:Corn price ratio. These are the highest N rates in the UW Extension guidelines and are recommended where manure and legume credits are the only source of N for fields on farms where the land base for spreading is limited. These high rates already take into account the uncertainties in estimating N availability from manure applications; therefore, they already include the 20% addition to the N rate that is allowed in the 590 Nutrient Management Standard if all N applications are from organic sources. Total N applications in excess of the rates shown in the following table are not allowed, with the following exception: if the entire N amount is supplied by organic sources of N (manure, legumes), then up to 20 lb per acre N can be applied in starter fertilizer.

Table 1. Maximum allowable N application for corn (as of crop year 2013)

* If the entire amount shown here is supplied through organic sources, some starter N fertilizer (up to 20 lb N per acre) can be applied before the warning notices are given.

 

Wheat maximum N application rates

Table 2. Maximum allowable N application for wheat  (as of crop year 2013)

* Soils in the Loamy group that have less than 2% Organic Matter (OM) use the Sandy group maximum allowable N rate. Loamy soils with greater than 10% OM have maximum allowable N rates that are 30 lb N per acre lower than those shown in the table.

 

 

Legume crop maximum N applications

Most legume crops can fix sufficient N from the air to ensure adequate growth without applying additional N to the soil; therefore recommended N fertilization rates for most legume crops are zero. Legumes will use available N in the soil, however, in preference to fixing their own. Thus manure N applied to legume crops is not considered to be at risk of loss through leaching if it does not exceed the crop N removal rate.

The 590 Standard allows applications of manure to legume crops that do not exceed the annual N uptake by the legumes or removal by seeding year legumes and companion crops. The table below shows the first-year available manure N application rate allowed for each of the legume crops in SnapPlus.

Table 3. First-year available manure N application rates allowed for legume and legume plus companion crops*

*Some SnapPlus legume crops such as peas and snap beans are not included in this table because N removal in the harvested portions of the crop is similar to their N fertilizer recommendation.

 

Note: The 590 Standard does not allow commercial fertilizer N applications where there is no N recommendation, as is the case with most legume crops. However, due to the difficulty that sometimes occurs in obtaining N-free P2O5 or S fertilizers, SnapPlus does not give an excess N warning if up to 70 lb of the legume N allowance is applied as commercial fertilizer if that fertilizer includes required nutrients.

Crops other than corn or legumes maximum N application rates

If commercial N fertilizer is applied in any amount: Total N applications, including N in starter, should not exceed the UW recommended rate for the crop. For non-legume crops other than corn, there is only one N rate recommended for a given crop or, in the case of potatoes, crop and yield range combination.  Thus you will get a warning notice in SnapPlus when fertilizer N (including starter) is applied alone or in combination with legume credits or manure at a higher-than-recommended rate for any crop. 

If only organic sources are applied: The 590 Standard recognizes that there will always be some uncertainty in estimating manure N availability due to the effects of variability in manure nutrient contents, uneven application rates, and weather. As a result, if all of the N applied in a given crop year comes from organic sources (manure and/or legume credits), estimated available N is allowed to total 20% more than the recommended rate before a warning notice is given. This 20%exceedance allowance is described in WI NRCS 590 Technical Note III B.

Avoiding excess spring, summer, and fall N applications on soils with a high nitrate leaching potential

Soils that have a high nitrate leaching potential are highly permeable (P) soils, soils where the water table is likely to be within 12 inches of the surface at some time during the year (W), and soils with bedrock within  identified in the Restriction Features box that can be viewed from the Field screen and the Nutrient Application Planner. The 590 Standard section IV. B. places restrictions on fall and late-summer nitrogen applications on all of these soils and on growing season N fertilizer applications on P soils as outlined below. If these restrictions are exceeded, the excess N applications will appear in red on the cropping screen and a non-compliance message will appear in the Nutrient Application Planner and in the Compliance Check report. If the planned application is allowed but the application must be delayed, SnapPlus will display a guidance message.

Fertilizer N application restrictions on high nitrate leaching potential soils:

•On P, W, and R soils, no fall commercial fertilizer N is allowed except for up to 36 lb per acre on fall-seeded crops or in fertilizers that contain other nutrients (P2O5 or S). This restriction also applies to areas with less than 5 ft of soil over bedrock and within 1000 ft of municipal wells.

•On P soils, spring and summer fertilizer N applications need to be either a) in split-applications with more than half of the N recommendation applied after planting, b) applied with a nitrification inhibitor (only suitable for ammonium forms of N), and c) use a slow release fertilizer for the majority of the recommended N if it is applied at or before planting.

Fall applications of manure with more than 4% dry matter:

•On W, WR, and WP soils, do not exceed the crop N recommendation or 120 lb N, whichever is less

•On P and R soils, if there is a growing crop in the fall, limit rates to the crop N recommendation or 120 lb, whichever is less. Otherwise limit the rate to 90 lb N acre or delay applications until soil temperatures are less than 50 degrees or October 1, whichever is first.

Fall applications of manure with less than 4% dry matter:

•On W, WR, and WP soils, applications cannot exceed 90 lb except up to 120 lb N can be applied if one of the following is true: a) a nitrification inhibitor is used with the manure, b) there is an over-wintering crop or cover crop c) a cover crop is going to be planted within 2 weeks, d) the application is unincorporated, or e) application is delayed until soil temperatures are less than 50 degrees or October 1, whichever is first.

•On P and R soil, applications must always be delayed until soil temperatures are less than 50 degrees F or October 1 AND a) they must be unincorporated or b) the manure must be applied with a nitrification inhibitor.