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Sustainable Agriculture Literature Review - Boulder County

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6.2 Fertilizers<br />

Fertilizers provide nutrients to improve plant growth and crop yield. Nitrogen is vital to a<br />

plant’s ability to develop proteins and enzymes, which then helps the plant grow. 463<br />

Fertilizer use depends on several factors including soil type, soil fertility, climate, crop<br />

rotations, and price. Although some farmers use organic fertilizers (plant, animal, or<br />

mineral based) and animal manure, synthetic commercial fertilizers are the main type<br />

used in U.S. agriculture. 464, 465 After petroleum fuel and oils, the highest expenditure on<br />

manufactured inputs in Colorado is fertilizers (Figure 24). 466 Commercial fertilizers can<br />

be economical, but like all types of fertilizers, when the plant requirements do not<br />

balance with the amount of fertilization, excess nutrients can contribute to water<br />

contamination. 467 More information on the effects of fertilizers on water contamination<br />

can be viewed in section 4. Water Pollution.<br />

Of the total commercial fertilizer use in the U.S., nitrogen-based fertilizers comprise the<br />

largest portion, with a 56 percent share compared with 24 percent for potash, and 21<br />

percent for phosphate (Graph 11). 468<br />

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Graph 11: U.S. Commercial Fertilizer Use, 1965-2002 469<br />

The cost of commercial fertilizer is greatly increasing. Since nitrogen costs can be the<br />

largest fertilizer expense for farmers, the overall cost of inputs is rising for conventional<br />

farmers. The United States Department of <strong>Agriculture</strong> (USDA) states, “because natural<br />

gas is the main input used to produce ammonia, which, in turn, is the main input used to<br />

produce all nitrogen fertilizers, the volatile and upward-trending price of natural gas in<br />

recent years has affected the price and supply of ammonia, and, thereby, the supply and<br />

price of nitrogen fertilizers, which is a great concern to U.S. agriculture.” 470<br />

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