It is in fact very interesting to try to write books (se blogroll down to the right). It becomes necessary to penetrate issues, think it over, collect facts and figures. But there is a problem: it competes with writing blogs.
Nitrogen experiments on good sites show the following.
Yield increases with 30-40 kg grain for each additional kg N. This continues until the yield is about 500 kg/hectare below the maximum. If we consider this stage:
Economy: 1 kg N (SEK 10) has given 30 kg grain (SEK 1,5). That is more than 12 times the investment.
Energy: about 35 MJ are needed for one kg N. The energy content of grain is about 15 MJ/kg. For input of 35 we get 450. Nitrogen fertilization is a very energyefficient measure.
Greenhouse gases: 1 kg N means release of about 8 kg CO2eq (manufacture 0 soil). That means about 0,2 CO2eq per kg grain. With diesel etc the sum will be 0,25-0,30.
Nitrogen leaching: Both old and new experiments show that in this stage no nitrogen residues are left.
But – there is more to gain. First one step. say 30 N with in average 15 kg grain/kg N. Then a final step with 20 kg N giving in average 8 kg grain/kg N. Let us consider the last step.
Economy: for 1 kg N (SEK 10) we get 8 kg grain and a total of SEK 12. Still profitable.
Greenhouse gases: we got 8 kg grain for the input. We use 1 kg CO2eq per kg grain. This is inefficient. It is almost better to cultivate new land.
Leaching: according to experiments and models nitrogen additions at this level will increase longterm losses with about 30% of added N. That means 0.3 kg for the addition of 1. In other situations the society pays about SEK 100 pre kg N to reduce lieaching. That is a value of SEK 30. The profit from the fertilizer at the top was 2.
