Also
see predicting corn grain yields
In the figure above 4 yield potential equations are reported for winter
wheat, spring wheat, dryland corn and irrigated corn. As is noted,
the 4 equations are really quite similar. This is important when
considering that the winter wheat equation came from data in Oklahoma,
spring wheat from North Dakota, South Dakota, and Mexico, and Corn (both
irrigated and dryland), from Mexico, Nebraska, and Oklahoma. Each
production region (country or state specific) may well have minor
adjustments that are needed (variety, planting date, etc.), but for the
most part these yield potential predictive equations should be accurate.
Regardless, what is apparent here is that all grain yield prediction
equations will have the same form. The importance of the yield potential
equations is that they accurately reflect what the "yield potential"
will be for the growing conditions encountered within a specific year.
"Yield potential" changes from year to year in the exact same field,
largely due to temporal variability. Also, looking at the graphs,
our estimate of yield potential is the "yield" you hope to grow given
the "current" growth rate (on the day of sensing), thus, the outer edge
of the data set is used, and estimated by adding 1 standard deviation
along the entire exponential curve. For all crops (see figures
below), very few data points were encountered in the upper left hand
corner, noting that this outer edge represented a rather clean upper
boundary. As is noted above, the YP0 equation for wheat is
somewhat different that the other crops, largely because many of the
days from planting to sensing have GDD<0 (growing degree days or
Tmin+Tmax/2 - 4.4°C), where growth is not possible. The growth
curve (biomass produced per day), estimated using NDVI (excellent
predictor of biomass) has proven to be a reliable parameter for
estimating harvested grain yield in winter wheat, spring wheat, and corn
(both dryland and irrigated). Actual data for all equations is shown
below.
