Objective  Understanding the release patterns of various nutrients from different organic fertilizers is conducive to the application of organic resources and the improvement of soil fertility.

  Method  An incubation experiment was conducted at a constant temperature in water in the laboratory. Six kinds of organic materials, including five kinds of commercial organic fertilizers which were made of cow manure (COM), pig manure (PM), chicken manure (CHM), biochar (BC), straw compost (SC) and Chinese medicine residue (CMR). The contents of macro-elements (N, P, K) and medium and trace elements (Mg, Ca, Mn, Cu, Zn, B) were determined, and the nutrient releasing curves were fitted with Langmuir equation.

  Result  The nutrient release rates of the six organic materials were all fast in the early stage but slowed down in the later stage. The cumulative release rates of nitrogen from CHM and BC were 75% and 58% at the end of incubation, which were significantly higher than other treatments. The cumulative release rates of available phosphorus from all the organic materials were generally low, as they were only 20%-30% across the organic materials. In contrast, the cumulative release rates of available potassium were generally high (54%-91%), and CHM was the highest. The release patterns of the medium and trace elements were significantly different among treatments. The cumulative release amounts of Mg and Mn from BC were the highest among all organic materials. While the cumulative release amounts of Cu, Zn and B were significantly higher under CHM treatment than those under other treatments. In addition, the cumulative release amount of Ca from COM was the highest among the treatments. Langmuir equation performed well across the nutrients as the predicted release amounts were positively correlated with the observed values (P < 0.05). Moreover, the parameters of the equations further confirmed the above findings.

  Conclusion  The type of organic fertilizers affects the release patterns of different nutrients. Generally, CHM is a better choice than other fertilizers. An appropriate organic fertilizer can be selected according to the requirements of plant and/or soil. Our study contributes to the selection of organic fertilizer in improving soil fertility.