Providing Nitrogen Organically is Best
Nitrogen is extremely important for plants, but 70 percent of it is in the air, in an unusable form. Soil bacteria transform this atmospheric nitrogen into a form plants can use. Typically, this is done through nitrogen fixing bacteria like the types that are present on many legumes. However, if soil bacteria are absent, plants require some other source of nitrogen. In conventional commercial agriculture, synthetic fertilizer is typically used—in massive quantities.
Synthetic fertilizers increase plant biomass, so farmers enjoy higher crop yields in the short run. However, a large amount of this nitrogen ends up going to the wrong places. Plants can only use a limited amount of nitrogen, so the excess gets released into the air as a potent greenhouse gas, and into waterways and ultimately oceans, resulting in dead zones.
On average, only half of the added fertilizer is taken up by the plants—the other half is lost immediately to runoff and evaporation. This is even worse with vegetable crops, which can lose up to 80 percent of added nitrogen. However, in spite of all this excess nitrogen, the soil itself becomes depleted in nitrogen, since most of the nitrogen-fixing bacteria have been killed off.
Nitrogen pollution reduces oxygen levels in seawater, which causes plankton and other organisms to die off. The Gulf of Mexico dead zone covers 7,000 square miles—an area the size of New Jersey—largely the result of nitrogen leakage down the Mississippi River from massive corn growing operations.
But it’s a completely different story with organic farming. There is minimum leakage of nitrogen because it’s released slowly and taken up again by living organisms, and there is much less water runoff. Small amounts of nitrogen are continuously brought into the system by nitrogen-fixing bacteria. Also, cover crops such as vetches, oats, peas, and other legumes and manure continuously release nitrogen into the soil.
Synthetic nitrogen fertilizers are extremely costly in terms of energy. Fertilizers account for 50 percent of the energy use in conventional agriculture. Studies show that using cover crops (crop rotation) when growing corn or soy can reduce nitrogen leaching by 70 percent, as well as beginning to rebuild the soil in just two to three years.