Nitrogen is an essential nutrient for pasture growth. It is supplied by clovers or other legumes, which fix it from the atmosphere, or by fertiliser. Animals take in nitrogen when they eat pasture and excrete most of it in urine. Cattle urine applies nitrogen to patches of soil at very high rates, so a large amount can be leached through the soil and may enter the ground water. This water eventually reaches streams, ponds or lakes and, if the nitrogen content is high enough, can encourage aquatic weed growth. In wetland areas, some nitrogen is lost to the atmosphere as nitrous oxide.
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