Prior to application of manure, the following parameters need to be assessed in order to determine if nutrient application is appropriate. The pre-application field assessment will walk you through applying these steps to the application process. An ARM Field Assessment 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 a pollution event.
- Water Table
- Available Water Holding Capacity (Soil Moisture)
- Field Characteristics
- Field Cover
- Application Method
- Current field Conditions
- Application Setback Distances
- Vegetative Buffers
Each of these parameters will determine the ability to apply or not to apply to your individual fields. The Manure Spreading Advisory and Application Risk Management Worksheet will guide you through the process of evaluating if ambient and field conditions are appropriate for manure application and at what rate.
In order to apply manure at appropriate times throughout the year, it is vital to have an understanding of the climate trends in your area, as well as seasonal weather patterns and current conditions. The forecast is one of the most important parameters to check prior to application of manure or grazing events. In order to avoid negative soil and water quality impacts (i.e., runoff, soil saturation, compaction, etc.) and properly manage crop irrigation needs, the critical forecast characteristic that should be observed on a daily basis is precipitation.
In general, runoff from applied manure has a lower risk if there has been no significant rain for two days prior to application (soil moisture is less than 80%), and limited rain forecasted within 24 hours (<0.10 inches) and 72 hours (<0.50 inches) after application. These guidelines will vary with soil type and saturation.
If rain has occurred, check soil conditions thoroughly prior to application. A high soil moisture content will tolerate less rain and be more prone to runoff than a low soil moisture content. If more than 0.5 inches of cumulative rain is expected in the 72 hours following application, consider postponing application until more favorable conditions arise. Do not surface apply if a hard, sustained freeze is expected the same night, or if more than 1 inch of snow is predicted. These events will increase the risk of surface runoff.
For more weather and precipitation forecast information, click HERE.
- Ideal Forecast: No rain 2 days prior to application, no rain within 24 hours of application, and no significant rain (>0.5 in) forecasted in the 72 hours days post-application.
Water table level is a concern as it leads to soil saturation/impermeability and transfer of nutrients to ground water. The water table level 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. If the water table is within 24 inches of the surface, thoroughly monitor tiles after applying manure. If any discharge of manure occurs, address immediately by capping tile.
- Ideal Water Table: Water table must be greater than 12 inches from the surface; 24 inches or more is ideal.
The higher the soil moisture, the less likely your soil will be able to transfer applied liquid from the surface into the soil profile, thus increasing the possibility runoff. Different soil types will have different thresholds of soil saturation. Sand will be the lowest, while silt and clay will have the highest saturation rates.
If the moisture content of the soil is greater than 90%, application is not recommended. Between 70-90%, application is permitted, but may be limited by soil type, recommended application volume, and equipment limitations. Traffic on soils with a high saturation rate can lead to compaction and runoff. Below 70% moisture, no soil saturation restrictions are in place.
- Ideal Soil Moisture: Soil moisture should be less than 80% of saturation.
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 (maintain a setback distance from 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 cap them in case a manure discharge occurs. Do not apply over tiles with less than 24 inches of soil cover and always observe tiles after application. If you don’t know these parameters, do not apply closer than 100’ from tiles.
Observe all seasonal manure setback distances from areas that are conduits to surface waters (i.e., tiles, ditches, streams, etc.).
- Ideal Field Characteristics: Take individual field characteristics into account prior to application: slope, soil type, low spots, tiles, etc.
Field cover is an important consideration for application of manure. Vegetation slows overland runoff and allows it to infiltrate into the soil profile thus limiting runoff events. Application to bare or sparsely vegetated fields (<50% cover) will have a much greater risk of runoff than dense forage stands and should be avoided during high runoff risk times. Only established, dense (>70% cover) grass or cover/relay crops grown for harvest are permitted for application during high risk times. Sparse vegetation (<50% cover) have limited application rates and seasonal restrictions.
Established vegetative buffers adjacent to waterways are recommended for application to sparsely vegetated fields to prevent and/or filter runoff. Vegetation should be greater than 3 inches high at application to reduce runoff transport.
- Ideal Field Cover: An established and/or dense (>80% cover) grass stand or cover crop greater than 3 inches in height, should be in place prior to application during high risk times.
Not all methods of liquid manure application are appropriate all year. In general, methods that inject or incorporate manure into the top layer to the soil are best for limiting transport. 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. If using a big gun, only apply when transport via wind drift is low and stay back the recommended setback distances at all times (at least 40 feet year round).
Make sure any type of manure application equipment is properly calibrated prior to use.
- Ideal Application Method: Apply manure below the grass canopy using best methods (i.e., aerator) or inject into the soil for annual crops.
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, frozen ground, snow cover, vegetation cover less than 3 inches in length, unmonitored tiles, and/or sparse or dead vegetation. All of these field conditions should be evaluated prior to application.
- 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, swales, wet area, or other area of concern identified by your planner, you must adhere to all setbacks specified in your nutrient management plan. Setbacks will change throughout the year based on seasonal considerations and should be assessed on a daily basis.
- Ideal Application Setback Distances: Adhere to seasonal setback distances throughout the year.
Any areas that have the possibility of runoff to a neighbor, waterway, swale, or water body and cannot be managed with setback distances alone need to be contained with a vegetative buffer of some kind to reduce the risk of runoff contamination. Vegetative buffers (i..e, filter strips, field borders, etc.) need to be maintained to function properly. If buffers are well established, have dense vegetation (>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.