Prior to application of manure, the following parameters must to be assessed in order to determine if nutrient application is appropriate. An ARM Field Assesesment Worksheet should be filled out for each field you are considering applying manure to prior to application. Failure to assess any of the following parameters could result in application under unfavorable conditions, which could lead to resource pollution.

Forecast
Water Table
Available Water Holding Capacity (Soil Moisture)
Field Characteristics
Field Cover
Application Method
Current field Conditions
Application Setback Distances
Vegetative Buffers

Forecast. The forecast is one of the most important parameters to check prior to winter application of manure. This will be one of the primary indicators of application risk. In general, application will not be limited by the weather if there has been no significant rain for 2 days and no forecasted rain within three days after application. If more than 0.5 inches of rain is predicted in the 3 days after application, it is recommended that application be postponed. If the forecast is favorable, then the other risk factors need to be evaluated prior to application.

• Ideal Forecast: No rain 2 days prior to application, no significant rain (>0.5 in) forecasted for 3 days post-application.

Water Table. The water table present in your field will depend on soil type, season, and recent weather conditions. If the water table is high, manure has a greater opportunity to leach into groundwater and/or be transferred to surface waters. If the water table is greater than 24 inches from the surface, the water table will not be the limiting risk factor for application; if it is between 12 and 24 inches, application will be limited by this parameter; if less than 12 inches from the surface, no application is permitted. Maintain your water table by making sure your drainage infrastructure (i.e., tiles, ditches, etc) is in good working order.

• Ideal Water Table: Water table must be greater than 12 inches from the surface; 24 inches or more is ideal.

Available Water Holding Capacity (AWC)/ Soil Moisture. The available water holding capacity (AWC) is a measure of the saturation of your soil. The lower the AWC (or the higher the soil moisture %), the less likely your soil will be able to hold and infiltrate applied manure into the soil and the greater the runoff possibility will be. If the moisture content of the soil is greater than 90%, application is not recommended. Between 70-90%, application is permitted, but will be limited by recommended application volume and equipment limitations. Below 70% moisture, no AWC restrictions are in place.

• Ideal AWC: Soil moisture should be less than 90% of saturation.

Field Characteristics. The characteristics of your field are very important to consider prior to application. Some characteristics may limit application on specific areas of a field (i.e., ponding, tiles, low spots, etc). You must take into consideration slope (prefer to apply to <3% slope), swales (don’t apply in swales), soil type (if the field is mixed, apply only to the appropriate soil types), low spots (areas where ponding may occur), and tiles. If tiles are present in your field, know where they are, where they empty to, and have a way to shut them down in case a manure discharge occurs. Do not apply over tiles with less than 24 inches of cover and always observe tiles after application. If you don’t know these things, do not apply closer than 100’ from tiles.

• Ideal Field Characteristics: Take individual field characteristics into account prior to application: slope, soil type, low spots, tiles, etc.

Field Cover. Field cover is an important consideration for winter application of manure. This system does not permit manure application to bare or sparsely vegetated fields, nor relay/cover crops that will not be harvested. Only established, dense (>70% cover) grass or cover/relay crops grown for harvest are permitted for winter application. Sparse vegetation (<50% cover) may have limited application rates or restrictions. Established vegetative buffers adjacent to waterways are recommended for winter application to prevent and/or filter runoff from fields.

• Ideal Field Cover: A, established and/or dense (>70% cover) grass stand or cover crop should be in place prior to application.

Application Method. Not all methods of liquid manure application are appropriate for wet season application. In general, methods that inject or incorporate manure into the top layer to the soil are best. If manure is surface applied (i.e., big gun sprinkler, splash plate, wagon), it is recommended that it be applied in a way that minimizes clumping and delivers liquids and/or solids below the grass canopy. Unincorporated, mounded solids are not an acceptable method for winter application. Recommended application rates may determine the type of equipment that can be used for application. Make sure equipment is properly calibrated prior to application.

• Ideal Application Method: Apply manure below the grass canopy using best methods.

Current Field Conditions. Current field conditions need to be visually evaluated prior to application. If there are any of the following conditions present, application may be limited or not permitted: ponding or standing water, compacted soils, saturated soils, fozen ground, snow cover, vegetation cover less than 3 inches in length, unmonitored tiles, and/or sparse or dead vegetation. All of these field conditions are evaluated prior to application on the ARM Worksheet.

• Ideal Current Field Conditions: Limited or no application if ponding, standing water, compacted soils, saturated soils, sparse vegetation, or unmonitored tiles are present.

Application Setback Distances. If your field is adjacent to a waterway, surface tiles, or wet area, you must adhere to all setbacks laid out in your nutrient management plan. Setbacks will vary by field, and may increase based on current field conditions. For instance, if ponding is noted on the field, investigate why and find out if it is running off into a waterway. If it is just a low spot and not flowing into a ditch or other waterway, you may apply manure near the ponded area. If it is running off into a waterway, you must exercise a 100 foot manure setback from the area.

• Ideal Application Setback Distances: Adhere to setback distances outlined in your Plan.

Vegetative Buffers. Any areas that have the possibility of runoff to a neighbor, waterway, swale, or water body need to be contained with a vegetative filter strip or field boarder to reduce the risk of runoff contamination. Vegetative buffers need to be maintained to function properly. If buffers are well established, have dense vegitation (>70% cover), and grass height is more than 3 inches in length, runoff pollution from application is reduced. If buffers are not maintained properly, manure setback distance may increase.

• Ideal Vegetative Buffer: Grass, cover crops, filter strips, and field boarders should be dense and maintained for proper runoff containment.

Each of these parameters will dictate the ability to apply or not to apply to your individual fields. The Application Risk Management Worksheet will guide you through the process of evaluating if ambient and field conditions are appropriate for winter manure application and at what rate.