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Did you apply your fertilizer correctly?


Lets figure out how to replenish your soil for this years pumpkin crop.

The vegetable man, wanted to plant pumpkins in a small garden plot 25 ft
wide and 25 ft long.  This means he has a 25ft X 25ft = 625 sq ft to
fertilize.  The vegetable man now called the pumpkin man checked the
chart and from previous experience of natural losses , that he needs
about 1.5 kg of nitrogen and 0.5 kg of phosphorus per 100 m square (3
lbs N/100 sq ft and 1 lb P/1000 sq ft).  He understnd that additional
potassium is seldom required, but its level should be checked
preiodically with a soil test.  Very sandy areas and peaty or high
organic areas are exceptions in that soils in there areas are often
deficient in potassium.  The pumpkin man soil is silt loam with a
excellent supply of organic matter, does not require additional
potassium at this time.

The proper way to calculate the amount of fertilizer to apply is to
divide the number of kilograms or pounds of nutrient required in 100 m
squared or 1000 sq ft y percentage of nutrient in the fertilizer.

Since the pumpkin man soil is slightly basic ( high PH, he wants to use
monoammmonium phosphate 11-55-0 and ammonium sulphate 21-00-00 which are
both acidic in nature. The pumpkin man starts by calculating how much
phosphorus to apply

1 lb of  phosphrous required       1.0 
----------------------------------       = ------   = 1.8 lbs of 11-55-0
per 1000 sq ft
                55%/100                         0.55

Since the fertilizer 11-55-00 also supplies some nitrogen, the pumpkin
man needs to know how much actual nitrogen is in the 1.8 lbs  will be
applying.  He does this by multiplying (instead of dividing) the weight
of nitrogen required by the percentage of nitrogen in the 11-55-0.

1.8 	lb of 11-55-0 X 11%/100 = 1.8 X 0.11 = 0.2 lbs of nitrogen per
1000sq feet.

The pumpkin man wants to apply a total of 3 lb of nitrogen per  1000 sq
ft.  Therefore, he must subtract the amount of nitrogen being applied in
the 11-55-00. 

3.0 	lb - 0.2 lbs = 2.8 lbs of nitrogen still needed.

Now he can calculate how much 21-0-0 to apply.

2.8 	lbs of nitrogen required      2.8   
-----------------------------------  = -----  =   13.3 lbs of
21-0-0/1000 sq ft
           21%/100                          0.21

But the pumpkin man garden in not 1000 sq ft so less fertilizer is
required to bring nutrients back up to optimum levels.  To calculate the
right amounts of fertilizer, he divides the weight by 1000 sq ft and
multiplies by his true area of 625 ft.

1.8 	lb of 11-55-0
--------------------- -   X 625 sq ft = 1.2 lb of 11-55-0
  1000 sq ft

13.3 lbs of 21-0-0
----------------------  X 625 sq ft  = 8.3 lbs of 21-00-00
   1000 sq ft

All fertilizers should be applied as accurately as possible.  Use a
weight scale or a measure cup to measure the fertilizer.  It takes
approximately 2.5 cups to measure a pound.

The pumpkin man knew people would whine that he did not discuss organic
fertilizer instead.  So...one day he saw house manure on sale at one of
the garden centers.  Its analysis id 0.6% N -0.2%P - 0.6%K. To compare
this fertilizer, he calculated the following.

3 pounds of N      3
-----------------    = ---  = 500 lbs of manure per 1000 sq ft.
0.6% / 100           .006

500 lbs / 1000 sq ft   X 625 sq ft = 312 pounds of manure for the
garden.

Cost for this quantity of manure are many times greater than the
chemical equivalent.  Moreover, the manure is much more difficult to
apply and incorporate.


DUNCAN DELETE
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