Author(s)

Martin Bachmaier

Technische Universit?t München, Center of Life Sciences Weihenstephan, Freising, Germany.

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 provides an estimate of the modeled function and thus also an estimate of the economic optimum, N_opt. Obtaining the accuracy of such estimates by confidence intervals for N_opt is subject to the model assumptions. The dependence of these assumptions is a further source of inaccuracy. The N_opt estimate also strongly depends on the N level design, i.e., the area on which the model is fitted. A small area around the supposed N_opt diminishes the dependence of the model assumptions, but prolongs the confidence interval. The investigations of the impact of the mentioned sources on the inaccuracy of the N_opt estimate rely on N rate trials on the experimental field Sieblerfeld (Bavaria). The models applied are the quadratic and the linear-plus-plateau yield regression model.

Confidence Interval; Economic Optimum; N Rate Trials; Quadratic Model; Linear-plus-Plateau Model

Bachmaier, M. (2012) Sources of inaccuracy when estimating economically optimum N fertilizer rates. Agricultural Sciences, 3, 331-338. doi: 10.4236/as.2012.33037.