Applications of Manure for Nutrients: What Exactly are You Getting?

As harvest of permanent crops wraps up and growers look around at options for banking P and K in the soil reservoir, organic sources of nutrients are common choices. Materials such as of raw manure, food waste and compost are applied by the truckload to supply valuable nutrients. While these products can offer a sizeable nutrient load, there can also be a downside associated with their use.

A typical lab analysis for nutrients of dairy manure is in the 1-1-1 range, and the 2-2-2 range for poultry litter. A 5 ton/ acre application could supply 100 to 200 lbs of each of the essential nutrients of nitrogen, phosphorous and potassium. If the dairy is near, product and trucking costs are low, and application equipment is available. For certain crops, this may be a tempting option for nutrients. But other than a cheaper source of nutrients, what else are you getting? Here are a few potential problems:

1. A balanced nutritional fertility program is our goal in production ag - providing the right blend and quantity of nutrients at the right time. There is a reason that we don’t fertilize mature orchards with triple 15.  Almonds, for example, use NPK in an approximate ratio (8-1-10), not 1-1-1. If we apply enough manure to meet the crop’s K demand, we will over apply for N and P. Excess and unused nutrients are a possible source of contamination to surface and ground water.
2. A complete nutrient analysis for manure may reveal the heavy metal content, as well as high levels of sodium and chloride. Manure reflects the animal’s diet and salts are often a big component. Salts applied to the soil from a couple tons of manure may not have a huge impact on plant health, but ten tons to the acre may have a different result.
3. Humus, completely decomposed and stabilized organic material, and the water soluble portion of humus, humic acids, are extremely beneficial in production ag systems for the impact they have on soil aggregation, soil tilth and their contribution to improved nutrient uptake. Manure, however, is a raw, unstable organic matter.  It is not humus, and it contains little humic acid.
4. Manure, food waste, even unfinished compost, all consist of raw, un-decomposed and unstable organic material. When incorporated into the soil, it must first be microbially digested before nutrients are available for plant uptake. Rather than providing an expected quick nitrogen bump to the crop, the microbial decomposition process actually immobilizes plant available nitrogen. Nutrient availability may be months or years after application.
5. On crops that are harvested off the orchard floor, like almonds or walnuts, or crops that are eaten fresh, such as fruits and vegetables, food safety is such a priority that the use of manure is often prohibited. Saving a few bucks on nutrients with manure applications, while potentially introducing salmonella and e-coli contamination of our food is not a risk worth taking.

Before using manure, run a sample through the lab and get a complete analysis that includes nutrient content, C:N ratio, heavy metals, EC, percent moisture, etc.  Do the math and calculate pounds of nutrients needed for the crop and pounds of nutrients applied.  Get the food safety pathogen test for e-coli and salmonella.  Weigh the benefits with the liabilities and then make your decision based on the facts.

- Don Wolf, Agronomist, Western Business Unit