Manure nutrient management is a cyclic process that includes:
- determining crop nutrient need,
- choosing a nutrient source,
- selecting and calibrating a manure application rate to deliver a target nutrient rate,
- monitoring crop performance and soil test values, and
- adjusting future application rates based on crop and soil monitoring.
Manures are unbalanced in nutrient content. When applied to meet crop nitrogen need, they usually will supply more phosphorus and potassium than is necessary for crops. Monitoring phosphorus and potassium via soil testing every three to five years is recommended to avoid excessive accumulation.
Unlike fertilizer, manure has variable nutrient content, depending upon site-specific factors (e.g., bedding, moisture, and storage or composting). See Table 2 for typical values.
For the current growing season, apply manure based on its ability to supply plant-available nitrogen to meet, but not exceed crop needs. Keep in mind that over-application of some products can damage plants with too much soluble salt.
Composts are lower in plant-available nitrogen than are most raw manures. Composting raw manure kills weed seeds and pathogens, facilitates storage, and makes a more uniform material that is easier to apply. For typical compost nutrient analyses, see Table 3.
Byproducts from cities and food processing facilities have nutrient value and are sometimes available for use on farms. See Table 4 for examples.
Manures and specialty products that contain more than 4% total nitrogen should be applied at low rates based on plant-available nitrogen supplied. See Table 5.
Use published values for manure nutrient content (Tables 2–5) with caution. Laboratory analyses of manure can improve the accuracy of manure nutrient application rates. For best results, send samples to laboratories that have demonstrated proficiency in performing manure analyses. Under Additional Resource, see the Lists of Laboratories and Consultants section of this publication for more information. Other organic materials can be analyzed for nutrient content using the same laboratory methods used for manure.
Calibration worksheets for manure spreaders that provide several options for monitoring manure application rates are included in this publication. Keeping records of manure nutrient application rates on a field-by-field basis can assist in evaluating and modifying manure application programs.
This publication is written for both organic farmers and other farmers who use manure. For details on organic farming standards, refer to the National Organic Standards in Additional Resources.