Dairy managers are extremely busy this time of year with corn silage and grain harvest, wheat planting and manure hauling. It’s tough enough finding time, people and equipment to get all these things done, let alone making sure the right amount of manure nutrients get applied according to soil tests, manure analysis and crop removal in each field.
Have a plan. Nutrient recycling through crops is not only economically sound, but it is environmentally safe when managed well. Large dairy operations, especially those which purchase most or all of the feed utilized, face serious challenges in getting manure nutrients back into crops that can utilize them. It’s time for all livestock producers to put a manure nutrient management plan in place and make sure the entire farm is in compliance with environmental requirements.
Seek the assistance of your county soil and water conservation district in getting your nutrient management plan together. Just getting the manure out of the storage and onto crop land is not good enough.
Watch P levels. There are some principles that should be considered by all producers who are applying manure to crop land:
1. There is no agronomic justification for raising the soil test phosphorus (P) levels above those which provide adequate nutrients for growing crops.
2. Increasing soil test P levels at the soil surface increases the pollution potential of a field, especially where no-till production systems are used.
3. Site characteristics, manure nutrient management, cropping system and erosion/runoff abatement practices all affect the quantity of manure that can be safely applied to a given field.
How much can I apply? To be more specific, many factors influence manure application rate:
1. Soil test and manure analysis (How much is there, how much can be safely added?);
2. Crop nutrient needs;
3. Field runoff potential is affected by: Whether manure is incorporated or surface applied; slope; moisture content of soil; temperature of soil and whether or not soil is frozen; surface residue; drainage.
What should the soil test analysis of a well-balanced soil look like? For typical mineral soils in the northeast Ohio/western Pennsylvania area you should see:
* pH: 6.3 to 7.0
* Lime Test Index: 68 to 70
* Phosphorus (P): 15-45 parts per million or 30 to 90 pounds per acre
* Potassium (K): 245 – 420 pounds per acre. (Soils that have had manure applied over several years are likely to have significantly higher P and K levels.)
* Calcium (Ca): 800-16,000 pounds per acre.
* Magnesium (Mg): 150-2,000 pounds per acre.
How much manure can you apply without interfering with the proper balance of nutrients in your soils? To evaluate the level and balance of nutrients in a field you need to look at total nutrient levels and several nutrient ratios.
There is only so much room for nutrients such as Ca, P, K, and Mg, to be held (absorbed) tightly by soil. This capacity is known as the cation (cat-eye-on, which means positively charged ion) exchange capacity (CEC).
For best crop growth, the available cations should be available within certain desired ranges and within certain desired ratios. A well-balanced mineral soil in our part of the country will have a CEC of 5-20 and should have approximately 65 percent of the CEC made up of Ca, 10 percent as Mg, 5 percent K, and 20 percent hydrogen (H).
These values correspond to a Ca:Mg ratio of 6.5:1, a Ca:K ratio of 13.1:1 and a Mg:K ratio of 2:1. Most field crops respond well to nutrient levels in these ranges.
When you apply fertilizer or manure, you should try to keep or return these levels and ratios to desired levels.
What about nitrogen? Nitrogen (N) is present in the soil in negatively charged anions such as nitrate (NO3), and ammonium (NH3). These anions are highly soluble in water, are not held by the soil particles and readily leach below the root zone or onto drainage water.
Ammonia is volatile and is readily lost into the atmosphere. Nitrate is converted by bacteria into nitrite (NO2) during wet weather and is also lost into the atmosphere.
Fertilizer and/or manure application recommendations are designed to at least account for nutrient removal by the current crop being grown (annual nutrient application). If you ask for it, many labs will also give you build-up recommendations to bring the soil nutrients to optimum levels for the type of crops you grow on your particular soils.
The OSU Extension Bulletin E-2567, “Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa,” provides additional nutrient recommendations and soil test interpretation information.
There is considerable research that shows that livestock producers are getting very little to no value at all from the nitrogen in their manure. You should use plant tissue analysis to find out how well your crops are utilizing manure nutrients applied.
There are many other factors such as soil compaction, root health, and rainfall during the growing season that also have important influences on manure nutrient uptake by plants. Incorporation of livestock manure during or soon after application is known to improve the utilization of manure nutrients and reduce the risk of pollution.
(The author is an agricultural extension agent in Columbiana County. Questions or comments can be sent in care of Farm and Dairy, P.O. Box 38, Salem, OH 44460.)