(2) An agronomist samples the soil in a field to a depth of 24 inches. A sample

Question

(2) An agronomist samples the soil in a field to a depth of 24 inches. A sample of this soil is sent to a laboratory, where it is determined that this soil contains 10 mg/kg of plant-available sulfur. Soil bulk density is estimated to be 1.2 g/cm a. Calculate the weight of an acre of this soil, to a depth of 24 inches, in lb/A. b. Calculate the amount of plant-available sulfur in this soil, in lb/A, to a depth of 24 inches. (Hint, don't do any English/metric conversions here. Remember what mg/kg means). c. A canola crop is going to be grown that will take up about 30 lb/A of sulfur. Is

Explanation / Answer

a)

weight of 24 in acre

1 A = 4046.86 m2

h = 24 in = 0.6096 m

V = a*h = 0.6096*4046.86 = 2466.96 m3

mass = D*V = (1200 kg/m3)(2466.96m3) = 2960352 kg

change to lb

m = 2960352 / 0.454 = 6520599 lb per acre

b)

plant available lb /A

10 mg / kg --> 10 * 10 ^-3 / 1000 = 10^-5

10^-5 * 6520599 lb per acre

65.21 lb of S per acre

c)

since 30 lb A < 65.21 lb of S per acre

there is enough lb of S

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