Development Of Large Tablet Controlled-release Urea For Rice

To solve the problems of over-used nitrogen fertilizer application,low nitrogen use efficiency and environment pollution in rice field,large tablet urea(LTU)was produced by International Fertilizer Development Center which could satisfy the need of rice with one-time fertilizer application.However,LTU must be put deeply to avoid the rice burnt and also increase the labor use.These problems could be solved by coating the LTU to controlled-release fertilizer.Therefore,it is very important to select a proper kind of coating material which is easily obtained and degraded.LTU(diameter 16 mm)was molded by conventional urea prills(diameter 0.5～4 mm)and coated by polyurethane(PU)from castor oil to produce large tablet controlled-release urea(LTCRU).Nano fumed silica was added into the coating materials to prolong the release longevity largely.With the help of 3D scanning technology,scanning electron microscope(SEM),transmission electron microscope(TEM)and Fourier transform infrared spectroscopy(FT-IR)and other methods,the fertilizer cores,coating material and nitrogen release characteristic were characterized.The results are as follows:(1)With the help of 3D scanning technology,the average surface area per gram of urea prill and LTU were 1257.78 mm~2and 359.36 mm~2respectively.The surface area per unit mass LTU is only one third of urea prill.With same coating content,compared with controlled-release urea based on urea prill,LTCRU could save two thirds of coating materials.(2)Nano fumed silica(NFS)was added into the coating materials to modify the castor oil based PU coating.The micro structure of fertilizer coatings were characterized by SEM.NFS were uniformly distributed on the surface and cross section of coating shells.After modified by NFS,the holes on the surface and cross section of coating decreased and the release longevity was prolonged greatly.With 3%coating contents,the release longevity could reach to 140 days.Two release pattern were discovered during water incubation.There was no volume change of LTCRU which had holes on the surface and cross section of coating in pattern 1.Water could get into the coating and lead to the dissolve and release of urea.There existed obvious volume change of MLTCRU which no obvious holes on the coating shell in pattern 2.The volume of MLTCRU became bigger during release process which is owing to the osmotic pressure between inside and outside of the fertilizer.(3)LTCRUs were evaluated by lysimeter experiment of rice.Compared with the yield of conventional urea prills in same nitrogen level,LTU and LTCRU improved the rice yield by22.67%and 50.61%,respectively.Also,they could improve the height,SPAD value,dry weight and effective tiller number of rice and decrease the ammonia volatilization in rice field.