Nitrogen fertilizer makes up 48% of rapeseed energy balance

Studying the energy balance of biofuels is important, certainly when they are produced from low yield crops such as corn or rapeseed. One of the main energy inputs in the production of such crops is made up by fertilizers. Earlier, we pointed to in-depth research into the fertilizer requirements of tropical energy crops, and now a study prepared for the French Enviroment and Energy Management Agency (ADEME) and the Centre Technique Interprofessionel des Oléagineux Métropolitains (CETIOM - which unites oilseed and vegetable oil producers) looked at the fertilizer inputs of oilseed crops grown in temperate climates, most notably in France. It found [*French] that of all oil crops grown there, rapeseed ('colza', 'canola') utilises most nitrogen-based fertilizers.

Rapeseed oil is increasingly used as a pure plant oil (PPO) in diesel engines, as well as in commercial biodiesel production ('rapeseed methyl-ester', RME), especially in Europe. The study looked at the 'seed to oil' energy balance of different oil crops (sunflower, soy, rapeseed, linseed), and found that rapeseed energy balance is dominated by the input of nitrogen-based fertilizer. Not less than 48% of all the energy inputs used to cultivate the crop can be tracked back to nitrogen, one of the three basic plant nutrients.

Nitrogen-based fertilizers are commonly synthesized using the Haber-Bosch process, which produces ammonia by reacting natural gas-derived hydrogen and nitrogen. This ammonia is applied directly to the soil or used to produce other compounds, notably ammonium nitrate and urea, both dry, concentrated products that may be used as fertilizer materials or mixed with water to form a concentrated liquid nitrogen fertilizer. About 80% or more of the 110 million tonnes of ammonia produced annually is used for fertilizing agricultural crops. The cost of natural gas makes up about 90% of the cost of producing ammonia.

André Pouzet, chief of the CETIOM, puts the study in the context of biodiesel production. Given rapeseed's energy balance, and the fact that these energy costs make up 45% of the total energy inputs involved in biodiesel production, the share of nitrogen's energy inputs amounts to roughly 25% of the total energy inputs of the finished biofuel. This high proportion must prompt rapeseed producers to try to reduce nitrogen fertilizer inputs and ultimately to strengthen the energy balance of biodiesel.

However, there is a great regional and interannual variability in the amount of nitrogen fertilizer applications and their effects on rapeseed production, with some producers achieving much better results than others. Since 1999, the dosages used have steadily declined because of new fertilization technologies that make applications more targeted and efficient. On average, these technologies have resulted in a reduction, between 1999 and 2005, of 181 to 167 units for the spring season:
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"The importance of these technologies that allow for a finetuned fertilisation strategy is to reduce both over-fertilisation and under-fertilisation. We think it is possible to reduce total use of nitrogen by around 10 to 15 units", explains Pouzet.

Three main research areas have now been identified to make nitrogen fertilisation more efficient still.

First of all, fertilizer producers are and should be investing in reducing the energy costs of their production process. Secondly, more intense agronomic research and timing strategies must become more widespread amongst rapeseed farmers. A study by Agrricultural Chamber of the Eure-et-Loire region has shown that yield increases can be obtained by a better match of rapeseed varieties and fertiliser strategies, that result in a decrease of nitrogen needs. Third, Pouzet adds that fundamental research drawing on experiments with Arabidopsis (the 'fruit fly' for plant breeding research), has shown that new breeding techniques can result in non-genetically modified plants with lower nitrogen requirements.

The CETIOM chief streses that the energy balance of biodiesel made from rapeseed is positive, but that it can be strengthened by a range of efforts that spans all players in the field: agronomists, fertiliser producers, rapeseed growers and biodiesel producers.