Abstract: [Objective] The use of the slow/controlled release fertilizer is the development trend all over the world. In this study, wood residues were used as materials to make a slow release fertilizer shell based on its features of porosity, permeability and biodegradability. The fertilizers were loaded in the shell, and then the slow release rules were investigated by artificial rainfall simulation. The influence of shell's characteristics such as the species of wood residues, thickness and density of the shell on fertilizer releasing was studied in order to make the controlled release fertilizer shell which could be applied to the trees, flowers and other plants. [Method] The Pinus massoniana and Toona sinensis wood residues were used as raw materials to manufacture wood residues slow release fertilizer shell. The influence of shell's characteristics including the species of wood residues, the thickness and density of the shell on release rules of fertilizer were studied by artificial rainfall simulation. The artificial rainfall simulation could be controlled well and avoid the uncertainty and contingency of the natural rainfall. [Result] The results showed that the shell could slow down the release of fertilizer and keep a relatively stable release rate. In the control group without the shell, the initial release rate increased sharply and then fell down dramatically. The release rate was about 65.46% at the 90 d compared with less than 39.20% in the experimental group which represented a longer effective period of the fertilizer in the shell. The species of wood residues had great influence on release rate. The release rate was about 93.01% in Pinus massoniana shell at 210 d compared with 74.43% in Toona sinensis shell. Furthermore, the thickness of the shell also had significant influence on release rate. With the increase of the thickness of the shell, release rate of fertilizer presented a decreasing trend. The release rate of three groups with different thickness of 6 mm, 8 mm and 10 mm were 73.65%, 69.59% and 64.72% at 210 d, respectively. However the density of the shell had little influence on release rate. The release rate of three groups with different density of 0.50 g·cm^-3, 0.55 g·cm^-3 and 0.60 g·cm^-3 were 69.70%, 69.59% and 67.87% at 210 d, respectively.[Conclusion] Wood residues shell had an obviously slow release effect. The influence of the species of wood residues and the thickness of the shell on release rules of fertilizer were as follows: the release rate of fertilizer in Pinus massoniana shell was faster than that in Toona sinensis shell. With the increase of the thickness of the shell, release rate of fertilizer exhibited a decreasing trend. However, the density of the shell had little influence on release rate in this study. By selecting different species of wood residues and making different thickness of the shell, the controlled release fertilizer could be realized to meet the needs of different plants.

Key words: wood residues, slow release fertilizer shell, artificial rainfall simulation, shell's characteristics