Vol. 51—1997 - NorthEastern Weed Science Society

148
Appendix
Calculate the environmental expense E of the kg of herbicide and nitrogen fertilizer applied to
grow a yield f Y tons.
Y:= 5
Let herbicide r te h kglha increase from 0 to 2 kg/ha in ten steps of 0.2.
i : 0,1 .. 10
h i
= 0.2·i
Let the herbici e diminish the density of weeds w per square meter from a maximum of 500,
achieving a de ity of SOOleat an herbicide rate of 1/3.6 kglha.
w .= 500 ,,=3.6
x·
-n-h,
w. := w.e I
1 X
Let weeds dec ease yields by a maximum of 800/0and decrease yields to half 80% at a
density of 22 eeds per square meter.
\
Wi "1
(
= x 080 . w2 22 .=. ,
2 1/
1 X W + w.1
Let nitrogen 6 ilizerrate n kglha increase from 0 to 250 kglha in ten steps of 25.
n. = 25-j
J
rogen produce half the maximum, weed-free yield of 6 t1ha-but let the soil
of nitrogen.
n 2 := 50
Let theyield
killing weeds.
( nj + n s )
n s 50 Yf =y . -----
j x \ n j + n s + n 2
the weed-free yield set by nitrogen diminished by a fraction set by herbicide
ivided into the demanded Y tons, the t1hayield determines the area cropped.
r
y
y.. = Yf". 1
A· . =
I,J J '.
1,) y..
I,J
To convert int a common, environmental currency the hectares of land, kg of herbicide and kg
of nitrogen fert izer used, specify exchange rates.
e a := 100 e = 200 e n
Finally, for an i tegrated or holistic environmental expense, add three contstituent expenses.
The first is the change rate for cropping a hectare ofland times the hectares used. The
second and thi expenses are exchange rates for herbicide and fertilizer per kg times the kg of
each used. Th kg used are the hectares of land times the kg/ha rates of the two chemicals.
. E.. e·A t-eh·{A.h\. e ·(A .·n\,
I.J a 1. \ i .j 1 n \ I .J J: