Dynamic model for the effects of K‐fertilizer on crop growth, K‐uptake and soil‐K in arable cropping. 1. Description of the model

Abstract

Abstract. To provide a practical aid to improving fertilizer practice a mechanistic model was developed that can be readily calibrated for widely different crops. Most of the inputs are easy to obtain and the others, the amounts of fixed soil‐K and the velocity constants for fixation and release of soil‐K, can be readily measured by a novel procedure which is described.The model calculates for each day the potential increase in plant weight and the increment in root length, from the current plant mass, its %K and pan evaporation. It calculates the maximum amount of K that could be transported through soil to the root surfaces. It modifies this potential uptake by taking account of the ‘feedback’ of plant K on root absorption to give the actual uptake and a new %K in the plant. It calculates the radii of the depletion zones around each root increment and the interchange between the solution, exchangeable and fixed‐K in these zones and also in the undepleted regions of soil. Routines are included for the effects of weather on the various processes. Differences between species are accommodated by selecting one of three algorithms for root growth and by adjusting the values of two crop‐K parameters that define the decline in a critical and a maximum possible %K with increase in plant mass per unit area.A simplified version of the model runs interactively on the Internet at: http://www.qpais.co.uk/moda‐djg/potass.htm