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_________________________________________
Problem Set #7
Due: Wednesday, November 24
th
1.
Whether or not nitrogen fertilizer is required depends on the crop grown and the yield desired. You want
to grow a crop of corn that yields 15 Mg (tons) per hectare.
Assume that the total amount of N required
to obtain this yield is
200 kg N/ha
and that the
sources of N are from exchangeable NH
4
+
and N
mineralization from soil organic matter
.
From the following information, determine whether N will
have to be added as a fertilizer; if so, how much
N fertilizer will have to be added per hectare?? Answer
the following series of questions to determine your answer.
Show your work!
Rooting depth = 20 cm
1 ha = 100 m x 100 m = 10,000 m
2
Bulk density = 1250 kg/m
3
1 kg = 1000 g
Exchangeable NH
4
+
= 0.014 g NH
4
/kg soil
Organic matter content = 4%
Nitrogen content of organic matter = 5%
a.
What is the mass of soil in the 20 cm rooting zone (kg) of one hectare? (soil volume x bulk density)
b.
What is the mass of nitrogen
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 Fall '10
 RandyDahlgren

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