Response of potatoes to N fertilizer: Dynamic model

SummaryA simulation model is described to interpret N fertilizer experiments on potatoes. It calculates the total growth of dry matter, the N uptake, the partition of dry matter and of N between tuber and foliage and the distribution of inorganic N down the profile for each day during the growing season.The validity of the model was tested against measurements of these parameters made at approximately fortnightly intervals on plots that received N fertilizer and those that received none in 4 experiments on a sand, 4 on a sandy loam and 3 on a clay soil.Simulated values were in reasonably good agreement with the measured values in all experiments. Overall the sums of squares of the differences between the simulated and measured values of the %N in the total plant, and the total amount of inorganic N in the top metre of soil and the logarithms of the total weight of dry matter, tuber dry weight, N uptake in the entire plant and N uptake in the tubers were each less than 25% of the sum of squares of the measured values about the mean.Only 9 inputs were required for the model. It was found essential to take account of differences in spring and summer leaching but not of inter-site differences in mineralization rate.