Pulses use half the non-renewable energy inputs of other crops

To feed a growing population, farmers have to provide their crops with the right nutrients. Nitrogen is the nutrient most needed in crop production, and the main input to manufacture nitrogen fertilizer is natural gas, a fossil fuel. Yet pulses are among the small group of food crops that draw their own nitrogen from the air we breathe. Pulses are able to do this through a symbiotic relationship with nitrogen fixing soil bacteria that live inside their root systems1. Instead of using fossil fuels to power the creation of fertilizer, pulses use solar energy to power a biological process that provides nearly all the nitrogen required for their growth. Pulses also improve the fertility of the soil, reducing the nitrogen fertilizer requirement of other crops grown in rotation, like wheat2. So pulses not only use half the non-renewable energy of other crops3, they also reduce the use of fossil fuels of an entire crop rotation.

Optimising biological N2 fixation by legumes in farming systems

This 2003 article in the peer-reviewed journal Plant and Soil summarizes research projects conducted by the United Nations Food and Agriculture Organization from 1972 to 1998. Research projects were conducted in both developed and developing countries, focusing on the ways in which the nitrogen contribution of pulses and other legume crops can be maximized.

The reasons why legumes and pulses are central to sustainable farming are explained, and then the methods for measuring the amount of nitrogen they produce are discussed in detail. Methods of enhancing the nitrogen production of legumes are then outlined.

Research has shown that there is enough genetic variation in many different legume crops to allow for plant breeding to improve their nitrogen-producing ability. The symbiotic rhizobia microbes that help pulses produce nitrogen could also be bred to be longer-lasting and more effective. In addition, the methods by which symbiotic rhizobia microbes are applied to pulse crops could be improved. Crop management to enhance soil quality and water availability is also important to allow the nitrogen added by the legume to be used by subsequent crops.

Effects of tillage method and crop rotation on non-renewable energy use efficiency for a thin Black Chernozem in the Canadian Prairies.

This study compared different crop rotations and tillage practices to see how they affect non-renewable energy use. It was published in the peer-reviewed journal Soil and Tillage Research in 2004.

The experiment included three different crop rotations and three different tillage practices. The three crop rotations were: 1) monoculture wheat; 2) wheat and flax; and 3) wheat, flax and peas. Each rotation was grown with conventional, minimum, or zero tillage practices. Energy use was determined by adding all the non-renewable energy used to manufacture, package, transport, maintain, and apply all inputs (such as fertilizer, fuel, and pesticide). Energy use efficiency was measured in three different ways: 1) the amount of grain produced per unit of energy input; 2) the ratio of energy output to energy input; and 3) the net energy produced (i.e. the energy produced in the harvested crop, minus the energy required to produce it).

After 12 years, the study showed that energy use efficiency was highest for the rotation that included peas. Non-renewable energy inputs required by peas were lower than flax or wheat. The addition of both peas and flax to the wheat-based crop rotation reduced total energy use by 13% compared to the rotation that added flax only. Growing wheat after another wheat crop required 8% more energy than if wheat was grown after peas. Improved energy use efficiency was attributed to the nitrogen supplied by the pea crop, reducing the need for added nitrogen fertilizer. Energy use efficiency was also improved when minimum or zero tillage practices were used to produce rotations that included peas or flax; however, tillage practices had no effect on energy use in monoculture wheat rotations.

This study confirms that adding peas to crop rotations can increase the efficiency of energy used in agriculture on the Canadian Prairies.

Decoding your fuel bill: What is your farm’s real energy bill?

This short article by researchers from Agriculture and AgriFood Canada and the University of Saskatchewan was published in 2008 in the peer-reviewed online journal Prairie Soils and Crops. It focuses on energy use in prairie agriculture.

The article first provides the historical background of energy use in prairie agriculture, beginning with the use of horses and oxen for power, followed by the mechanization of farming in the 1930s and 1940s, to the current trend of decreased tillage and increased fertilizer use. The major sources of energy use on prairie farms are reviewed: fertilizer, herbicides, and fuel to power and manufacture farm equipment.

Growing pulses and other legumes is highlighted as a way of reducing the nitrogen fertilizer requirement in agriculture. A pulse crop saves energy by producing nitrogen for itself and reducing the nitrogen requirement for subsequent crops. It also requires less energy to grow because there is no energy used to apply fertilizer. Overall, producing pulses requires only about half the energy of a cereal crop like wheat or barley.

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