SnapPlus indicates when you have exceeded the nitrogen application rate allowed by the Nutrient Management Standard 590 by including messages in the Nutrient Application Planner on the Management page.
When manure and/or fertilizer applications totaling more than the allowable N rate are entered in the Nutrient Application Planner box, an overapplication message and exclamation point symbol (!) will appear below the accounting table in the Nutrient Application Planner. You will also get a message if your applications do not meet the requirements for soils with high leaching potential (N restricted soils).
When an "N over" 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 explanation section of the compliance message.
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:
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.
Warning flags for excess N applications will be triggered based on the type of crop. These flags are summarized below and more information can be found in following sections.
The maximum allowable rates of N application for all soils are described for different crops in the following sections:
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.
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.
| Soil | Previous crops | Maximum plant-available N rate (Legume credits, Manure credits, This year’s manure, This year’s fertilizer) * lb/acre |
|---|---|---|
| Loamy: High yield potential | Corn, forage legumes, legume vegetable, or green manures | 210 |
| Soybean or small grains | 160 | |
| Loamy: Medium yield potential | Corn, forage legumes, legume vegetable, or green manures | 160 |
| Soybean or small grains | 150 | |
| Sands/loamy sands: irrigated | All | 230 |
| Sands/loamy sands: non-irrigated | All | 150 |
*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.
| Soil group | Previous crops | Maximum plant-available N rate (from Legume credits, 2nd and 3rd year manure credits, This year’s manure, This year’s fertilizer) |
|
|---|---|---|---|
| Winter wheat | Spring wheat | ||
| N lb/acre | |||
| Loamy* | Corn, forage legumes, legume vegetable, or green manures | 85 | 75 |
| Soybean or small grains | 65 | 55 | |
| Sandy (sands/loamy sands) | All | 115 | 105 |
| Organic | All | 0 | 0 |
* 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.
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.
| Crop | Yield range | Manure N allowed (lb/acre) |
|---|---|---|
| Alfalfa; alfalfa/brome; red clover; or trefoil, birdsfoot, seeding or established | <1.5 ton/a | 50 |
| 1.5 - 2.5 ton | 100 | |
| 2.6 - 3.5 ton | 155 | |
| 3.6 - 4.5 ton | 205 | |
| Barley for grain underseeded with alfalfa, alfalfa/brome, or red clover seeding | All yield levels, bu/a | 150 |
| Dry beans | 10-20 cwt | 75 |
| 21-30 cwt | 125 | |
| 31-40 cwt | 175 | |
| Oats for grain underseeded with alfalfa, alfalfa/brome, or red clover seeding | All yield levels, bu/a | 140 |
| All pastures with legumes | 0.5-1.9 ton | 55 |
| 2 -3 ton | 115 | |
| 3.1 - 4.0 ton | 160 | |
| 4.1 - 5.0 ton | 205 | |
| Small grain silage underseeded with alfalfa | 2 - 3.5 ton | 170 |
| Small grain & legume silage | 2 - 3.5 ton | 70 |
| Small grain & legume silage underseeded with alfalfa | 2 - 3.5 ton | 170 |
| Soybean forage | 2-3.5 ton | 170 |
| Soybean, grain and grain + straw | 15-25 bu | 75 |
| 26-35 bu | 115 | |
| 36-45 bu | 155 | |
| 46 bu or greater | 195 |
*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.
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.
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.
Flags for excess N are given on these crops when the plant-available N rate is 10 lbs over the allowable N rate described above.
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 have a non-compliance message 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.