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Abstract
Trials were conducted to produce certain local slow release fertilizers using either synthetic or natural materials. An evaluation for each fertilizer in the laboratory by evaluation their activity index and diffusivity urea fertilizers coating with sulphur, phosphogypsum or bentonite result in clear depression in the amounts of released nitrogen. The highest effect being found with both imported sulphur coated urea (SCU) next bentonite coated urea (BCU) next phosphogypsum coated urea (PGCU). Results indicate that the diffusivity is nearly constant for thickness of sulphur (404.67) cm2/sec and then it begins to decrease after one day dissolution time. This may be attributed to the fact that after certain dissolution time a shrinkage occur resistant to dissolution may be formed which inhibit the dissolution characteristics. Observed that an average value of (483.09) cm2/sec may be considered as diffusivity of urea through solid bentonite. from which it may be observed that an average value of (704.80) cm2/sec may be considered as diffusivity of urea through solid phosphogypsum. This can be attributed to fact that coating layer of urea that is formed by speaking resistant to degradation by the characteristics of each material