Living on air From nutrient back to air Loss of nutrient nitrogen In farming, most of the nutrient nitrogen is lost during harvest. Protein-rich – and therefore nitrogen-rich – plants are simply removed from the land. Farmers obviously need to replace the nutrient nitrogen they have removed in order to restore the fertility of the soil. That is not enough, however. Besides the nutrient nitrogen “lost” to the harvest, nitrogen is also lost to the air and soil in natural processes. Although the soil contains bacteria that convert atmospheric nitrogen into nutrient nitrogen, bacteria that do precisely the opposite are even more common. They convert the nitrogen back into a gas that evaporates into the air, so that it is once more unavailable for plant growth. Nutrient nitrogen that plants can absorb is mobile. The portion that the plant has not yet absorbed can be flushed away into the soil in heavy rain. Depending on the circumstances, part of it will leach from the soil into the ground water and surface water. The loss of valuable nutrient nitrogen is both natural and unavoidable. The nature and scale of nitrogen loss depend on the climate, the weather, the type of crop, the type of soil, and the degree of fertilization efficiency. The scale of the loss is roughly comparable to the amount of nitrogen contained in the crops removed in the harvest. I 11
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