The vegetable man, want to plant pumpkins in a small garden plow 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 check 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).
Additional potassium is seldom required, but its level should be checked periodically with a soil test. Very sandy areas and peaty or high organic areas are exceptions in that soils in their areas are often deficient in potassium.
The pumpkin man soil is silt loam with an 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 mono ammonium 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 X0.11=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
1000sq 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 man times greater than the chemical equivalent. Moreover, the manure is much Smore difficult to apply and incorporate.
