Release Dynamics Of Coated Fertilizer With Lixiviating Method And Rapid Method To Predict The Longevity Of Nutrient

In this paper,lixiviating method was applied to study the dynamics of coated fertilizer,the cumulative release curve of NPK showed sigmoid pattern,the processes of nutrient release accorded with the law:start with slowly release, constant release rate in the intermediate stage and end with the release rate decaying.The Richards,Logistic and Bertalanffy equations were applied to model nutrients release from coated fertilizers in static water under a constant temperature of(25±0.5℃).Analyse of correlation coefficient and standard deviation showed that the Richards equation was superior to Logistic and Bertalanffy and the Richards equation could describe the nutrients release characteristics of coated fertilizer exactly.The Richards equation was also used to describe the release characteristics affected by different extracting conditions(granule radius, extraction mode,temperature,eluant pH and fertilizer-water ratio).Increasing granule radius could reduce the release rate of different nutrients.Compare to the extraction mode of renewing eluant,the nutrients release rate of continuous mode was decreased,the linear release stage was increased and the time for maximum nutrient release rate was delayed.For all kinds of nutrients,increasing temperature could significantly speed up the release rate and shorten the longevity.When the temperature was 25,60,80℃respectively,the longevity of NH₄⁺-N was 87.1d, 10.2d and 44.7h respectively.Using Richards equation to regress the time,which required the cumulative release rate of 25℃equalling with that of 80℃,between 25℃extraction(t₂₅) and that of 80℃strengthening extraction for 25h and 12h(t₈₀,t′₈₀),the regression equations were as follows:t₂₅=6759.41×{1-0.336×exp[-0.01402×(t₈₀-82.97)]}^1/0.336 and t₂₅=5712.66×{1-0.645×exp[-0.00119×(t′₈₀-372.51)]}^1/0.645.Make use of those equations and the results of 80℃strengthening extraction,the longevity of coated fertilizer was predicted,there were 0.3%and 9.98%relative errors between the tested longevity and the predicted one.This could satisfy the need of production and application.