ABSTRACT
An economical optimal herbicide rate (EOR) was determined and assigned to each grid cell. This was based on observed weed species, density, and size that were used to calculate the total competitive load (TCL) of that grid cell and the predicted yield loss (YL):8,9
≡ × =
(17.1)
where D is density of weed species (i) ACI is adjusted competitive index value of weed species (i) with WeedSOFT®
2003 Kansas Version 8 (University of Nebraska, Lincoln, Nebraska) as the basis for adjusted competitive index values for each weed species
The TCL was then used to calculate the percent crop yield loss (YL) using a modiŽed rectangular hyperbola model:
Y (TCL slope) AdjustmentL = × × (17.2)
where the slope is the percent yield loss at low TCL the Adjustment is the factor that changes the linear portion of the model to
nonlinear at high TCL8,9
Actual crop yield loss (CYL) is determined as a function of the expected crop yield goal (kg ha−1):
CY
Y 100
yield goalLL =
×
(17.3)
The TCL predicted to remain after the postemergence (POST) herbicide application is calculated (PTCL):
PTCL TCL exp( k H)= × − × (17.4)
where k is the coefŽcient of the herbicide efŽcacy H is the herbicide application rate10,11
Once the PTCL is calculated, CYL is recalculated using Equations 17.1 and 17.2. ProŽt is calculated using the following equation:
PROFIT CY CP H HPL= × − × (17.5)
where CP is the expected price of the crop at harvest ($ kg−1) HP is the price of the herbicide ($ kg−1)
For each grid cell, the highest net proŽt was determined by optimizing the relationship between herbicide rate and actual yield. The herbicide rate generating the highest net proŽt was considered the EOR.
