Richards方程在描述包膜控释肥料氮素释放特征中的运用

Application of the Richards Equation to Describe Nitrogen Release Characteristics from Controlled Release Fertilizer (CRF)

【目的】筛选适合于描述控释肥料氮素释放特征的数学模型,为以数学模型预测预报控释肥料供肥特征提供理论依据。【方法】运用Richards,Logistic和Bertalanffy方程拟合在(25±0.5)℃恒温条件下包膜控释肥料在静态水中的氮素累积释放曲线。【结果】结果表明Richards函数能较好地拟合不同形状的氮素养分累积释放曲线,其拟合度优于通用的Bertalanffy和Logistic方程。3种方程中,Richards方程的特征参数更能精确地描述包膜控释肥料氮素释放特征,能反映出氮素养分最大释放速率出现的时间、累积释放曲线的形状等。【结论】Richards方程可用于拟合S型、抛物线型和双抛物线型3种类型的养分释放曲线;增加包膜厚度能降低控释肥料氮素养分在水中前期的溶出率,同时推迟最大养分释放速率出现的时间。

[Objective and Method] In order to select a suitable equation to describe nitrogen release and a mathematic model to predict nutrient release from CRF, the Richards, Bertalanffy and Logistic equations were applied to model nitrogen release from coated NPK fertilizers as controlled release fertilizer in static water under a constant temperature of （25 ±0.5）℃. [Result] The result showed that the Richards equation was applied to describe the precise nitrogen release curve of a different type. The Richards equation was superior to Bertalanffy and Logistic. Among the three equations, the characteristics of the Richards equation expressed the nitrogen release property, the time to the point at which the maximum amount released per unit time and the shape of the release curve of the coated NPK fertilizer. [ Conclusion ] In summary, the Richards equation fits models of three types of nutrient release curves, including the sigmoid pattern, parabolic pattern and double parabolic pattern. In using both parameters d and ti in Richards equation, one can easily judge model of nutrients release curve. Increasing coating thickness could decrease nitrogen release rate from CRF at early period of incubation and delay the time for maximum release of nutrient from CRF.