Problems in Developing Grass Seed Mixtures:

1. Determine the percent pure live seed in a bag of bulk seed of each of the following grasses/mixes:

Grass or Mixture Purity Germination PLS
  % % %
(1)  Smooth bromegrass 85 90 76.5
(2) Smooth bromegrass 40 75 30.0
  Orchardgrass 58 88 51.0
(3) Big bluestem 20 50 10.0
  Indiangrass 25 65 16.3
  Little bluestem 10 55  5.5
  Switchgrass  8 78  6.2
  Tall dropseed  3 20  0.6
  Inert matter and weeds 42 --  

2.  Farmer Brown plants 13 lbs of PLS smooth bromegrass per acre of the quality shown in (1) above

a.
 How many pure live seeds are being planted per square foot?
 
X PLS/ft2
13 lbs PLS/Acre		 = 20 PLS/ft2
6.5 lbs PLS/acre
X = 40 PLS/ft2

b.
How many pounds of bulk seed must be bought if 25 acres are to be seeded?
 

25 acres * 13 lbs. of PLS per acre = 325 lbs of PLS
 
325 lbs PLS
0.765 PLS		 = 425 lbs. bulk seed

3a. Farmer White wants to plant the following mixture on 50 acres. Calculate pounds of PLS for each species that Farmer White must plant to yield 20 PLS/ft2 for the whole mixture. How many pounds of PLS of each species must he buy for his project?

Species     Mixture as seeded
Big bluestem (BB) 40%
Indiangrass (IN) 25%
Switchgrass (SW) 25%
Sideoats grama (SO) 10%
     
Species Calculation
BB
IN
SW
SO		 0.40 * 6.0 lbs PLS per acre = 2.40 lbs PLS per acre * 50 acres = 120.0 lbs PLS
0.25 * 5.0 lbs PLS per acre = 1.25 lbs PLS per acre * 50 acres = 62.5 lbs PLS
0.25 * 3.0 lbs PLS per acre = 0.75 lbs PLS per acre * 50 acres = 37.5 lbs PLS
0.10 * 4.5 lbs PLS per acre = 0.45 lbs PLS per acre * 50 acres = 22.5 lbs PLS

3b. Farmer White contacts Seed Dealer A and gets the following info. Complete the table.
Species  Purity 
%		 Germination  
%		  PLS   Seed price 
$/lb PLS		  Seed price 
$/bulk lb
Big Bluestem
Indiangrass
Switchgrass
Sideoats grama		 75
65
97
92		 65
85
60
84		 0.488
0.550
0.580
0.770		 9.00
9.25
3.50
3.75		 4.39
5.09
2.03
2.89

3c. How many pounds of bulk seed of each species are needed to plant 50 acres?
Species Calculation
BB
 2.40 lbs PLS/acre 
0.49 PLS
* 50 acres = 245 lbs bulk
IN
 1.25 lbs PLS/acre 
0.55 PLS
* 50 acres = 114 lbs bulk
SW
 0.75 lbs PLS/acre 
0.58 PLS
 * 50 acres = 65 lbs bulk
SO
0.45 lbs PLS/acre
0.77 PLS
* 50 acres = 29 lbs bulk

3d. What would be the cost of seeding per acre if he buys from Seed Dealer A?
Species
Calculation
Cost
$/acre
BB
IN
SW
SO
2.40 lbs PLS per acre * $9.00 =
1.25 lbs PLS per acre * $9.25 =
0.75 lbs PLS per acre * $3.50 =
0.45 lbs PLS per acre * $3.75 =
21.60
11.56
  2.63
  1.69
37.48
4.   Seed Dealer B can supply Farmer White with his mixture, at $8.40/lb of PLS.  Is this a better buy for Farmer White? What is the price difference?
 
Amount of seed needed:
Cost of mixing own seed:
Savings by mixing seed:		 2.40 + 1.25 + 0.75 + 0.45 = 4.85 lbs PLS/acre
$37.48 / 4.85 lbs = $7.73/lb.
$8.40 - $7.73 = $0.67/lb
 
A total of $0.67/lb is saved using Dealer A

5. Rancher Black wants to plant 150 acres of Farmer White's mixture (question #3).  But Rancher Black already has some seed harvested from an unmowed meadow. The total dry weight after cleaning is 1650 lbs.  The analysis of seed obtained from the seed lab reads as follows:
Species  Purity 
%		  Germination 
%		  PLS 
Big Bluestem
Indiangrass
Switchgrass
Other crop and weed seed
Inert matter		 25
10
  5
  8
52		 60
60
70
--
--		 0.15
0.06
0.035
--
--

How many lbs of PLS of each species must Rancher Black buy to have adequate seed to plant the entire acreage at a rate of 20 PLS/ft2?
PLS
Species lbs. needed lbs. has lbs. buys
Big bluestem
Indiangrass
Switchgrass
Sideoats grama
2.40 * 150 =
1.25 * 150 =
0.75 * 150 =
0.45 * 150 =		 360.00
187.50
112.50
67.50
0.150 * 1650 =
0.060 * 1650 =
0.035 * 1650 =
 		 247.50
99.00
57.75
0
360.00 - 247.50 =
187.50 - 99.00 =
112.50 - 57.75 =
67.50 - 0.00 =		 112.50
88.50
54.75
67.50
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