ISSN: 1659-2751

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Nitrogen Mineralization Potential of Bokashi, Compost and Vermicompost Produced at EARTH University

Abstract

Organic fertilizers may be a viable alternative to the use of chemical fertilizers to provide the N required by a crop. The potential or capacity of any organic fertilizer to provide N must be known in order to avoid a deficiency or an excess of N resulting from the application of the organic fertilizer to a soil. The N mineralization potential of four organic fertilizers produced at EARTH University, a bokashi from Finca Comercial (FC), compost from Finca Integrada Orgánica (FIO) and a bokashi and a vermicompost from Finca Pecuaria Integrada (FPI), was evaluated. The organic fertilizers, in amounts equivalent to 20 Mg ha-1, were added to samples of a soil from a conventional management system and a soil from an organic management system. Triplicate samples of all treatments, including one control for each soil, were incubated aerobically at room temperature throughout 20 weeks. Mineralized NO3--N was determined in samples after 0, 2, 4, 6, 8, 10, 12, 14, 16 and 20 weeks of incubation. The results show that all four organic fertilizers mineralized very small amounts of N. The addition of bokashi from FC immobilized considerable amounts of available N already present in both soils. The C:N ratios of all organic fertilizers explain the results. Most of organic fertilizers had C:N ratios greater than the optimum (20:1) required to induce mineralization of N. Nitrogen mineralization potentials of the four organic fertilizers were also low, ranging from 28.7 mg kg-1 NO3--N of soil to 74.5 mg kg-1 NO3--N of soil. These potential amounts of mineralized N from the organic fertilizers would not meet the N requirements of various crops. In general, the organic fertilizers produced at EARTH University do not have an adequate N supplying capacity.

Key words: Organic fertilizer, bokashi, compost, vermicompost, N mineralization, N mineralization potential.

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