Disadvantages of Nitrogen fertilizers

Farmers use manure as a source of nitrogen for their crops and as a way to dispose of it. Many also apply commercial nitrogen fertilizer, since there's no way to know exactly how much nitrogen is in the manure. This practice ensures that the plants get enough of the nutrient to produce profitable yields. An unintended result can often be too much nitrogen, more than the plants can use before it washes away in rain, snowmelt runoff, or subsurface drainage to surface waters. Most of the nitrogen eventually ends up in rivers and eventually in seas, where it can create periodic dead zones. Marine animals either move out of these oxygen-starved waters or they perish. According to scientist Michael P. Russelle, using manure to fertilize legumes may help keep excess crop nitrogen out of bodies of water. Legumes can capture nitrogen from the air with assistance from bacteria that live in nodules on their roots. The bacteria convert the nitrogen into amino acids that plants use to make proteins. The bacteria in turn get nutrients and energy from the plants. For this reason, farmers usually don't apply manure or commercial fertilizers to these crops. In this case, the damage that the excess of nitrogen causes to the environment is diminished and If the legumes don't have enough nitrogen, they will start making their own. Russelle suggests that fertilization should be done in strictly controlled conditions, in order to reduce the risks of contaminating the soil and the water. By carefully planning fertilization, scientists are able to control pollution of the environment, discouraging the improper use of natural and commercial fertilizers. By using research results, scientists estimate how much of the crop nitrogen is supplied by nitrogen fixation and how much of it comes from other sources. This means that while water-quality experts and watershed managers will be able to use basin-scale maps to help determine good candidate areas for manure application to legume crops, farmers will need to use more detailed information about their fields to best use the manure to derive both production and water-quality benefits.