Calculate composts’ contributions before application

03/19/2013 04:03:00 PM
Monica Ozores-Hampton

Editor's note: A special thanks to Dr. Monica Ozores-Hampton at the Southwest Florida Research and Education Center for coordinating The Immokalee Report, of which the article below is part.

Compost can be used in conventional and organic fruit and vegetable production.

Feedstock for composting can be generated from yard wastes, biosolids, municipal solid waste, and animal manures such as poultry, dairy, horse, swine, cattle with and without bedding, and other biodegradable waste by-products from urban or agricultural areas.

Compost can directly affect soil bulk density, water-holding capacity, soil structure, soil carbon content, macronutrients and micronutrients, pH, soluble salts and cation exchange capacity, and biological properties (microbial biomass).

compost trialsMonica Ozorese-HamptonThe left plot received no compost and reflects that with lower plant biomass and iron deficiency. The right plot, which received compost, has higher plant biomass and no iron deficiency.Although compost is not considered a nutrient source or a fertilizer when used as part of a fertility program, its nutrient contribution should be calculated. 

The first step in building a fertility program for fruit and vegetables is to take a soil sample and send it to a soil laboratory for analysis of nitrogen, phosphorus and potassium (N-P-K) and micronutrients. These results can be compared to the local University of Florida crop recommendations for N-P2O5-K2O.

Second, select the compost based on local available materials and determine application rate, moisture and N-P2O5-K2O content, and N mineralization rate.

Then calculated the N-P2O5-K2O contribution from the compost and compare it to the crop requirements.

For example, poultry manure compost applied at 5 tons per acre with 40 percent moisture, 3 percent N content with 10 percent mineralization, 3 percent P and 2 percent K with 70 percent P and 80 percent K availability rate will contain 54 pounds of nitrate (NO3), 288 of P2O5 and 115 of K2O lb per acre.

Finally, determine the inorganic fertilizer that is needed in the fertility program.

Compost can improved soil physical, chemical and biological properties.

Nitrogen contribution can be low to medium, but P and K may be high to very high. Crop nutrient budgets can be a useful tool to account for nutrient inputs and outputs.

To download the University of Florida guide written by Ozores-Hampton on soil and nutrient management using compost, visit

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