Quantitative relationships for the dependence of growth rate of arable crops on their nitrogen content,dry weight and aerial environment

Summary Quantitative relationships for growth rate and its dependence on plant nitrogen concentration are developed from the results of experiments on potatoes, cereals and vegetables. The relationships appear to be of general applicability and most coefficients in them are similar for widely different crops.It is argued that during the main growing period (May–August inclusive) in Western Europe growth of crop dry matter may be limited by self regulatory mechanisms within the plant and is little affected by variations in the aerial environment when there is ample water and nutrients. Under these conditions both growth rate and the critical % N in the dry matter (the minimum % N at which growth rate is maximum) are simple functions of plant dry weight.It is deduced that when account is taken of the effect of plant weight on % N in the dry matter, growth rate is, as a close approximation, linearly related to % N until this reaches the critical value and constant at higher values.A computer simulation model based on these relationships enabled estimates to be made of the influence of measured plant-N concentrations on the increase, throughout the season, in the dry weight of potatoes and cereals grown with different levels of N fertilizer. There was good agreement between the estimates made in this way and the results of numerous field experiments.