Premium
Pooling Experiments Over Time to Quantify the Dynamics of Dryland Winter Wheat Yield Response
Author(s) -
Burt Oscar R.
Publication year - 1995
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1995.00021962008700020004x
Subject(s) - yield (engineering) , mathematics , precipitation , pooling , environmental science , agronomy , winter wheat , regression analysis , seeding , regression , linear regression , statistics , meteorology , computer science , biology , geography , materials science , artificial intelligence , metallurgy
This research had a dual purpose: (i) statistical estimation of winter wheat ( Triticum aestivum L.) yield response as a function of plant available water and applied N fertilizer from an 8‐yr experiment in north‐central Montana and (ii) illustration of the modeling methods that are appropriate in this type of research. Summer‐fallowed and re‐cropped treatments were pooled to obtain an indirect estimate of the extra amount of N made available by summer fallow, as well as to improve the implicit experimental design by providing the necessary variation in plant available water, particularly soil water at seeding. The statistical model was nonlinear regression with an error components disturbance term entering multiplicatively. A new flexible functional form is presented for crop response; it is a polynomial generalization of the Mitscherlich single‐factor equation. A major task was to validate the regression model by considering various types of specification errors, such as accounting for all concomitant factors associated with pooling the experiments over time. Mineralized N during summer fallow was found to be a negatively sloped linear function of precipitation during the fallow period; the average amount was 24.5 kg ha −1 . Nitrogen and water have strong interactions in shaping the yield response surface, and at high levels of both factors, more of either depresses yield. The depressing effect of N on yield at very low levels of water was clearly discerned.