Nitrogen, phosphorus and potassium supply capacity in four organic amendments

Abstract

Nitrogen, phosphorus, and potassium supply capacity was measured in 4 organic amendments. Analysis of total nutrient content, microbial bioassay, and greenhouse nutrient extraction methodologies were used and compared. The greenhouse assay was carried out using pure materials and a mixture 4:1 soil-organic amendment. Organic amendments were 1 vermicompost (cattle manure) and 3 composts (coffee, sugar cane, and orange wastes). The total nutrient content varied from 0.9-2.12% for N, 0.36 3.02% for P and 0.94-2.21% for K. With the microbial bioassay availability for N varied from 12-30%, 6-23% for P and 5-9% for K. The authors consider that the methodology makes a good estimation of N and P availability, but underestimates that fraction of K. With the greenhouse nutrient extraction, using pure materials, availability of N was 4-15%, 1-4 % for P and 6-49% for K. A high correlation between total nutrient content analysis and microbial bioassay was found and a good one between both laboratory methodologies and the greenhouse nutrient extraction, with mixtures but not for pure materials. Results of this study provide quantitative estimations of N, P and K availability for organic materials which could be used as a reference for future experiments.