Estimating Uncertainty of Economically Optimum N Fertilizer Rates. (8th March 2012) - Bachmaier, Martin
Abstract : Nitrogen rate trials are often performed to determine the economically optimum N application rate. For this purpose, the yield is modeled as a function of the N application. The regression analysis is commonly used to estimate the modeled functions and the economic optimum rate, N opt . However, computer programs do not calculate confidence intervals for N opt derived from quadratic yield response model or other commonly used models. The objective was to develop a method for computing and interpreting confidence intervals for N opt . These confidence intervals can be estimated using an online program VINO.EXE. For the N rate trials on the experimental field Sieblerfeld (Bavaria), confidence intervals were computed for a range of wheat and N fertilizer prices and for selected N rates for quadratic and linear plateau models. The latter concerns the comparison with confidence intervals based upon the linear-plus-plateau yield regression model. All intervals were found to be unexpectedly wide and their ranges were affected by N rates used in the calculations and by the choice of yield response model.