Fertilizer and Other Issues Affecting Energy Use

Although not purchased directly, large amounts of natural gas are used to manufacture ammonia and other nitrogen-based fertilizers. The average energy needed for fertilizer production is about 17,000 Btu per pound of nitrogen fertilizer (ammonia)  [13]. Net energy used for nitrogen fertilizer manufacture is several times greater than that energy needed to produce phosphorous (1725 Btu per pound) or potassium (600 Btu per pound) fertilizer or for pesticide manufacturing. For crops requiring large amounts of nitrogen, particularly corn, energy used to produce commercial nitrogen fertilizer can be equal to or greater then that used in all field operations. The energy to manufacture the nitrogen fertilizer for a corn crop re-quiring 120 to 200 pounds of nitrogen per acre would consume the equivalent of 15 to 24 gallons of diesel fuel. Using no more than recommended nitrogen rates will help maximum economic return and energy efficiency. A nitrogen cost to rate of return calculator can assist growers in determining the economic benefit of different application rates [14, 15].  Contact local Extension agents for your state’s recommendations.

Best practices such as crop rotation or planting cover crops that maximize nitrogen credits can greatly reduce fertilizer costs. Growing alfalfa, clover following wheat [17] or to a lesser extent soybeans or other leguminous crop or cover crops in rotation prior to corn [16], wheat or other grain crops reduces the need for nitrogen fertilizer. Or, consider using nutrients from other sources, such as manure. Manure nutrient availability varies with livestock species, manure storage and livestock production practices, and separation of liquid and dry components. Although general guidelines for manure nutrient content can be found in state Extension bulletins, periodic testing for nutrient analysis of manure will ensure a more accurate application.