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.
Relationship between INSEY (NDVI collected
once at Feekes 5, divided by the days from planting where GDD>0) over
34
sites, 1998-2004 for Winter Wheat (by site above, all sites below).
Relationship between INSEY over 6 sites in India, collaboration with
CIMMYT, 2005-2006.
Relationship between INSEY (NDVI collected once at Feekes 5, divided by the number of days from emergence to sensing) over 12 sites, 2001-2004 for Spring Wheat in Ciudad Obregon, Mexico.
