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 late summer and fall N application rates on soils that have a high leaching potential, and these are described in the section Avoiding excess 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.

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

 

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. Commercial N should not be applied to legume crops that do not have an N requirement unless it is an unavoidable ingredient of a fertilizer needed to provide other 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. In addition, if the entire amount 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.

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

Soils that have a high nitrate leaching potential are identified in the Restriction Features box that can be viewed from the Field screen and the Nutrient Application Planner. The 590 Standard places restrictions on fall and late-summer nitrogen applications these soils.

Fall and Late-summer N application restrictions on high nitrate leaching potential soils:

•Fertilizer N: No fall commercial fertilizer N applications except for no more than 30 lb per acre on fall-seeded crops.

•Manure N: When soil temperatures are greater than 50º, no late-summer or fall manure applications unless you:

•Manure N: When soil temperatures are less than 50º, no more than 120 lb available N per acre in manure applications.

•If a summer or fall manure or fertilizer application is made on a spring-seeded field with N restrictions a notification appears in the Nutrient Application Planner screen indicating:

•No fall fertilizer N can be applied to this crop on soils with a high N-leaching potential. If more than 30 lb N is applied in the fall to a fall-seeded crop, this message is generated: No more than 30 lbs. fertilizer N can be applied in the Fall to fall-seeded crops on soils with a high N-leaching potential.

•The 590 restrictions allow some flexibility in making late-summer and fall manure applications, but do not under any circumstances allow more than 120 lb available N per acre to be applied at that time. If fall manure available N applications on an N-restricted soil total more than 120 lb N per acre, the following warning message will appear in the Nutrient Application Planner screen: This field has fall or late summer N applications in excess of what is allowed for soils with a high N leaching potential.

•The late-summer and fall excess N applications will appear in red on the cropping screen and will be documented in the Compliance Check report.