Hello Ms. Hache,
   Thank you for your inquiry about the seed dry weight calculation.
   The calculation in the DSSAT manual should give you a fairly accurate
estimate of the seed dry weight. The equation is
Seeds wt dry (g/m2) = (ear wt undried x (seed subsample wt dry / ear
subsample wt undried)) / harvest area
The ear wt undried is the total ear weight (cob + seed) from the harvested
area. I think this is one place where there is confusion: Ear weight refers
to total ear wt undried that is recorded in the box that states, "Calculate
ear number (ears/m2) by dividing number of ears by harvest area (12.06 m2)
and record. Enter total ear weight (undried)." I should have made this more
explicit. The seed subsample wt dry is the seed dry weight from the box
just above the box with the seed wt dry equation. In this box it states,
"Dry seed and cob subsamples to constant weight at 70 C (approximately 7
days). Log seed and cob subsample weights (dry) separately." The ear
subsample wt undried is the wt recorded three boxes above the box with seed
wt dry equation. In this box it states, "Select a subsample of 10
representative ears for dry weight and seed number determination. Log ear
subsample weight (undried)."
   There is more than one way to calculate seed dry weight (g/m2) as you
have pointed out. However, in your calculation you don't need to include
the ear weights (total and subsample). All you need to do is use this
equation:
Seeds dry wt (g/m2) = (removed seed wt undried x (100 seed wt dried / 100
seed wt undried)) / harvest area,
or seeds dry wt (g/m2) = 915.2 x (17.88 / 37.77)/ harvest area = 433.2 g /
harvest area
Where removed seed wt undried is the weight of all seed removed from the 10
plants.
    Your method is a more direct method of calculating seed dry weight and
would be preferable over the method in the manual. The manual's method
assumes that the cob:seed ratio is the same among ears, which may or may
not be true. However, the manual's method is much less labor intensive,
especially if there is no sheller available. So, you may choose the method
depending on the availability of labor and machinery.
   I hope this helps.
Sincerely,
Richard


At 03:20 PM 11/27/01 -1000, you wrote:
>Dear Listers,
>
>I am using the equation for calculating Seed wt. dry (g/m2) in "Final
>Harvest Procedure for Maize" from DSSAT manual. The equation is :
>
>
>Seeds wt dry (g/m2) = ear wt. undried x (seed subsample wt. dry/ear
>subsample wt. undried)/Harvest area
>But when I apply the values (as an example) :
>Ear wt. (undried) :  776.1 g
>Seed subsample wt. (dry) : 17.88 g (this is the data from the 100 seed
>wt.dry)
>Ear subsample wt (undried): 1299.5 g
>Harvest area : 1 m2
>
>The result is 10.68 g of seed/m2.
>
>
>I wonder if "seed subsample wt (dry)" is not the weight of the 100 seeds we
>dried in oven, but a ratio of the 100 seeds wt. dry/100 seeds wt. undried,
>multiplied by the weight of all the seeds we removed from the cobs (from the
>10 representatives ears). Then the equation would be as follows:
>
>Seed wt.dry= [ear wt.undried x {removed seeds wt.undried x (100 seed
>wt.dry/100seed wt.undried)}/ear subsample wt.undried]/Harvest area
>Then,
>removed seeds wt. (undried) : would be all the seeds removed from the cobs;
>915.2 g
>100 seed wt. (undried) : 37.77 g
>
>
>The results would be 258.82 g of seed/m2.
>
>I hope my way of explanation is understandable. I would appreciate indeed
>your help in this matter. Looking forward to hear from you,
>
>
>Carolina Hache
>Graduate student
>Tokyo University of Agriculture and Technology
>Agricultural and Environmental Engineering Department
>