Assessing nutrient supplying characteristics of slow-release-compound fertilizer by ion exchange resin membrane

Continuous incubation experiment was conducted to study supplying characteristics of nutrients(N,P,K) in two slow-release-compound fertilizers(SRCFs) at constant temperature(25℃) in soil using ion exchange resin membrane(IERM) methods.A pot experiment was also conducted to study the coincidence of nutrients release of SRCFs and rice nutrient uptake.Results showed that the daily mean nutrients supplying rate of NO3--N and NH4+-N within 56 days of these two SRCFs amounted for 3.30% 58.1% of that of normal compound fertilizer(NCF).The daily mean supplying content of NH4+-N was higher compared to NO3--N.The relative percentage of daily nutrients supplying rate of H2PO4- and K+ to the application amount of P,K in two SRCFs accounted for 14.9%,23.2% and 92.7%,64.5% of these of NCF,respectively.An apparent slow releasing phenomenon of nitrogen and phosphorus nutrients of SRCFs in soils was observed.The daily nutrients supplying rate of NO3--N,H2PO4- in soil might be characterized by parameter b in the Elovich,and that of NH4+-N,K+ might be characterized by parameter b in parabola diffusion equations.The nutrients supplying characteristics of SRCFs tested by IERM in soil were similar to those of the soil itself.There were significant or high significant positive correlations between nutrients of SRCFs uptake by IERM and rice(r=0.869*0.994**).The results suggested that IERM was an ideal method to assess the nutrients supplying characteristics of slow-release-compound fertilizers in soil.