聚合物包膜NPK复合肥料养分释放滞后期的研究

Lag period of nutrient release from polymer-coated NPK compound fertilizers

聚合物包膜肥料养分释放的滞后期是指不释放养分或释放量很少的时期,主要由水分进入过程和养分溶解过程组成,滞后期的长短受这两个过程控制;滞后期的主要影响因素为包膜厚度、养分溶解度、养分组成等。以此为理论基础,模拟了聚合物包膜肥料养分释放的滞后期,推导出聚合物包膜肥料滞后期的方程为:tlag=kr/3(l/PhΔP+1/Dφ),估算了聚亚安酯类物质包膜NPK复合肥料(Multicote)中K+、NO-3、NH+4释放的滞后期。4和H2PO-由于养分离子本身的溶解性质不同以及养分间的相互作用,不同的养分离子的滞后期存在明显差异,与试验结果一致。同时,该模型还表明,当包膜厚度较薄时,对滞后期起主导作用的是养分溶解过程,只有当包膜厚度足够大时,才会对滞后期起主导作用。该模型将对聚合物包膜肥料的研制和应用提供重要的理论指导。

The lag period of nutrient release from polymer-coated NPK compound fertilizer was defined as the period in which the cumulative release of nutrients was almost zero. The lag period came from two processes: water was diffused (into) fertilizer granule, and the void was full of water; the nutrients were dissolved in the water in the granule void. (According) the two processes the main parameters that affect the lag period included membrane thickness, nutrients saturated concentration and the ion composition. Based on these results the lag period was modeled and expressed as following formula: t_(lag)=kr/3(l/P_hΔP+1/Dφ). Polymer-coated NPK compound fertilizers (Multicote), which were provided by Haifa Chemical, were used in this release experiment in water, and the lag period of the release of potassium, nitrate, ammonium and phosphorus was evaluated . Because of the difference of nutrients dissolving properties and their interactions the lag period for varying elements differed significantly, with a longer lag period for phosphorus. The modeled (results) were in line with the experimental results . In addition, this model also showed that the process of nutrients (dissolving) mainly controlled the length of lag period when the thickness of coated membrane was very thin and the coated membrane could control the lag period only when it was thick enough. Therefore, this model could be used to provide theoretical basis for the development and study of polymer-coated fertilizers.