Recent improvements in the energy efficiency of agriculture: Case studies from Ontario, Canada

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Energy used (GJ) per tonne of crop produced defines energy efficiency. Low energy use/tonne of crop produced indicates higher energy efficiency. Because of improved crop breeding (more stress tolerance, genetic gain) crop yields have increased. Concurrently, energy used has decreased. Based on an analysis of energy use/crop produced for Ontario's major row crops (corn and soybean), energy efficiency of crop production increased from 1975 to 1991. In corn, energy efficiency increased 49.8% from 87.95 l of diesel fuel equivalent (LDFE)/t of crop produced to 44.16 LDFE/t from 1975 to 1991. Total corn production (t) and yield (t/ha) increased by 60.0% and 20.1%, respectively, whereas energy use/ha (LDFE/ha) and total energy use (LDFE) decreased by 39.7% and 19.7%, respectively. For soybean, energy use/ha (LDFE/ha) decreased by 46.3% but total energy use (LDFE) increased by 93.8%. The increase in total energy use was caused by a 260.8% increase in soybean acreage (ha). Because the increase in soybean production (t) of 278.2% was much greater than the increase in total energy use (LDFE), energy efficiency increased 48.7% from 75.46 LDFE/t to 38.67 LDFE/t. The proportion that fertilizer manufacturing contributes to total annual energy use in corn decreased slightly (74.2–71.0%) between 1975 and 1991; however, energy use in fertilizer manufacturing declined by 42.4% because of the increased efficiency of manufacturing nitrogen fertilizers. Increased efficiency of fertilizer application also decreased energy use, although application is a much smaller proportion of the total energy use budget. Similar decreases occurred in soybean production. Our analysis of no-till systems using various herbicides and application rates indicated that the systems using the highest herbicide application rates required the least energy, because decreased herbicide application rates may require increased cultivation. This, however, depends on the timing (pre-plant, planting, post-emergent) and type (banded, broadcast) of application and is true only for newer herbicides with low application rates.