Abstract
AbstractFor efficient utilization of fertilizer, a practical means of expressing the residual effect of certain plant nutrients is needed. A descriptive model was developed to show the change in extractable nutrient levels with time assuming a rapid increase after fertilization followed by a slower exponential decrease. The information needed or parameters for the model include (i) the equilibrium soil test level, (ii) the magnitude of the initial sorption reaction, and (iii) a loss constant. These were determined for seven long‐term fertilizer studies with phosphorus (P). There was a large difference in P‐sorption capacity of the soils; all parameters reflected this difference. The initial sorption reaction was linearly related to rate of fertilization in some soils and quadratically in others. The model was applied to conditions in which fertilizer was applied at various time intervals. Good agreement between observed and predicted values was obtained. The main value of this model is to be able to calculate the amount of fertilizer needed to establish and maintain a given soil test level.
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