(1) An agronomist samples the soil in a field to a depth of 30 inches. A sample
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(1) An agronomist samples the soil in a field to a depth of 30 inches. A sample of this soil is sent to a laboratory, where it is determined that this soil contains 7.5 m/kg of plant-available nitrate-nitrogen. Soil bulk density is estimated to be 1.2 g/cm Calculate the weight of an acre of this soil, to a depth of 30 inches. a. b. Calculate the amount of plant-available nitrate-nitrogen in this soil, to a depth of 30 inches. (Hint, don't do any English/metric conversions here. Remember what mg/kg means). c. A corn crop is going to be grown that will take up about 150 lb/A of nitrogen. Is there adequate available nitrogen in this soil to meet that need?Explanation / Answer
a) Bulk density of the soil is 1.2 g/cm3
volume = area x depth
= 1 acre x 30 inchs
= 43560 sq foot x 2.5 foot
= 108900 cubic foot
= 108900 x 28316.8 cubic cm
Density of the soil is 1.2 g/cm
Thus weight of the soil would be, 108900 x 28316.8 x 1.2 g or 3700439.424 kg.
b) Now the soil contain 0.75 mg/kg of plant-available nitrate-nitrogen.
Thus 3700439.424 kg soil will have 3700439.424 x 7.5 mg or 27753295.68 mg or 27.8 kg plant -available nitrate-nitrogen.
c) The soil has 2.78 kg plant-available nitrate-nitrogen per acre.
If we convert this to lb/A then it will be 61.3 lb/A.
Thus there is not adequate nitrogen available to meet the need.
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