N-release characteristics of compound fertilizers coated with various minerals and its evaluation

This paper was to explore the N nutrient release characteristics, N uptake and use efficiency of Chinese cabbage and evaluation method of compound fertilizers coated with different minerals. Soil leaching and pot experiment methods were adopted. An inconsistent dynamics curve was observed using different methods. However, the results obtained under both methods showed that the using inorganic minerals could keep N as NH4＋-N for a long time，consequently reduce the risk of NO3－-N losses. But the effects of all the materials were not consistent. Although the accumulated amount or releasing rate of N was faster than the requirement of Chinese cabbage, the nutrients supplied was quite rational owing to the mineral and soil buffer capacity. Comparing to the common compound fertilizer，the N use efficiency of all the mineral-coated fertilizer was improved significantly. The effiect of applying Montmorillonite on N efficiency was the best, followed by Kaolinite. The effects of French chalk, Microsilica and Kieselgur on N efficiency were significantly lower than that of Montmorillonite and Kaolinite, but there were not significant different from each other. The physicochemical properties of mineral materials, such as water resistance, nutrient absorption and fixation, ion exchange capacity affected the nutrients release efficiency of coated-fertilizer. Using soil as release media might be closer to the truly release properties for the coated fertilizers depending on nutrient absorption and fixation mechanisms. All the factors, including nutrient forms, coated material properties, making technology, soil condition, tested plant etc, should be considered thoroughly for the slow/controlled fertilizers evaluation.