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Question
If a crop of wheat removes 20 kg of nitrogen per hectare of soil, what mass of the fertilizer, calcium nitrate Ca(NO3)2 would be required to replace the nitrogen in a 10 hectare field?
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Solution
Total area of the field = 10 hectare
∴ Total nitrogen that has to be replaced = 20 × 10
= 200 kg
Molecular mass of Ca(NO3)2 = 40 + 2 × 62 = 164
164 kg of Ca(NO3)2 contain 28 kg of nitrogen
Now, 28 kg of nitrogen is present in 164 kg of Ca(NO3)2
∴ 200 kg of nitrogen are present in `(164 xx 200)/28` kg of Ca(NO3)2 = 1171.4 kg
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