Answers to Hone Your Problem-Solving Skills Questions
1. 15 kg N/ha/yr for 20 years = 300 kg N/ha. Spread over 13,000,000 km2 (1.3 ? 109 ha), this is 3.9 ? 1011 kg N. If 10% of this is taken up, then there is 3.9 ? 1010 kg N incorporated into plant biomass.
With a 500:1 ratio of C:N, that would be 7.8 ? 107 kg C or 7.8 ? 1010 g C.2. 5 kg N/ha/yr for 20 years = 100 kg N/ha. Spread over 19,000,000 km2 (1.9 ? 109 ha), this is 1.9 ? 1011 kg N. If 10% of this is taken up, then there is 1.9 ? 1010 kg N incorporated into plant biomass. With a 500:1 ratio of C:N, that would be 3.8 ? 107 kg C or 3.8 ? 1010 g C.
3. On an annual basis, the greater C uptake would equal (7.8 ? 1010 g C + 3.8 ? 1010 g C)/ 20 years is equal to 5.8 ? 109 g C/yr. Annually, anthropogenic emissions are 10.4 Pg C, or 1.04 ? 1016 g C, so the increased sequestration due to N deposition would be only a 0.00006% increase in C uptake.