Sustainability
Pulses improve the sustainability of cropping systems


Just as pulses provide a number of nutritional benefits that positively impact human health, pulse crops produce a number of different compounds that feed soil microbes and benefit soil health. Pulse crops have a significant impact on soil biology, increasing soil microbial activity even after the pulses are harvested1. Pulses have also been shown to exude greater amounts and different types of amino acids than non-legumes2, 3 and the plant residues left after harvesting pulse crops have a different biochemical composition (e.g. Carbon/Nitrogen ratio) than other crop residues4. The ability of pulses to feed the soil different compounds has the effect of increasing the number and diversity of soil microbes2, 5.

Crops grow better in soils that are more “alive” with a diverse array of soil organisms, as these organisms break down and cycle nutrients more efficiently, feeding the crops as they grow. In addition, a large, diverse population of soil organisms acts to ‘crowd out’ disease-causing bacteria and fungi, making for healthier plants. Growing pulse crops in rotation with other crops enables the soil environment to support these large, diverse populations of soil organisms5.

References

1. Johnston, A.M., Clayton, G.W. and Miller, P.R. 2007. Introduction to “Pulse Crop Ecology in North America: Impacts on Environment, Nitrogen Cycle, Soil Biology, Pulse Adaptation, and Human Nutrition”. Agronomy Journal. 99: 1682-1683.
2. Gan, Y.T., Zentner, R.P., Campbell, C.A., Biederbeck, V.O., Selles, F. and Lemke, R. 2002. Conserving soil and water with sustainable cropping systems: research in the semiarid Canadian Prairies. Presentation to 12th ISCO Conference, Beijing, China.
3. Steen Jensen, E. and Hauggaard-Nielsen, H. 2003. How can increased use of biological N2 fixation in agriculture benefit the environment? Plant and Soil. 252: 177-186.
4. Lupwayi, N.Z. and Kennedy, A.C. 2007. Grain Legumes in Northern Great Plains: Impacts on Selected Biological Soil Processes. Agronomy Journal. 99: 1700-1709.
5. Lupwayi, N.Z., Rice, W.A. and Clayton, G.W. 1998. Soil microbial diversity and community structure under wheat as influenced by tillage and crop rotation. Soil Biology and Biochemistry. 30: 1733-1741.
Introduction to "Pulse Crop Ecology in North America: Impacts on Environment, Nitrogen Cycle, Soil Biology, Pulse Adaptation, and Human Nutrition"

Published in Agronomy Journal in 2007, this is a short article that provides a broad overview of the benefits of pulses as well as key directions for future research. It is the introduction to a symposium about pulse crops held at the annual conference of the American societies for agronomy, crop science, and soil science.

To begin with, the current status of land seeded to pulses in North America is reviewed. In the period from 1991 to 2006, the area seeded to pulses increased more than seven times. The nutritional benefits of pulses are then discussed. In addition to their high protein and fibre contents, pulses also contain compounds called phytochemicals that promote good health. Next, the environmental impact of pulses in terms of reducing greenhouse gas emissions is considered. The article also covers the positive impact pulses have on beneficial soil microbes that enhance plant growth. Finally, the ability of pulses to adapt to changing climate conditions is examined. Overall, pulses are playing an increasingly important role in North American agriculture.

Conserving soil and water with sustainable cropping systems: research in the semiarid Canadian Prairies

This article was prepared for the 2002 International Soil Conservation Organization conference held in Beijing. It was written by several researchers from Agriculture and AgriFood Canada. The paper summarizes two research projects conducted in Saskatchewan that looked at the effect of pulses on water use efficiency and soil quality.

One of the studies was long-term (more than 30 years) and included continuous wheat, wheat/fallow, or wheat/lentil rotations. The other study was short-term (two years) and included oilseeds, wheat, and pulses (lentil, pea, and chickpea).

The two studies found that using pulses reduced the leaching of nitrates, which minimizes the possibility of groundwater pollution. Including pulses also resulted in better soil quality than continuous wheat. In particular, pulses increased soil organic matter and promoted larger, more diverse populations of soil microbes. Rotations that included pulses required less nitrogen fertilizer, particularly when pea was grown. Pulses, especially pea and lentil, also tended to conserve water for the following crop. Overall, rotations that included pulses improved water and nutrient use efficiency, increased yields and raised protein concentrations.

How can increased use of biological N2 fixation in agriculture benefit the environment?

This peer-reviewed article summarizes the benefits that legumes and pulses provide. The article discusses nitrogen production but focuses in particular on the other effects legumes have on the environment. Examples include pulses as well as tree and pasture legumes grown around the world. The article was published in the journal Plant and Soil in 2003.

A major benefit of pulses is to reduce the need for nitrogen fertilizer and the energy used in its manufacture, transportation, and application. But pulses have other effects, too. Pulses and other legumes can increase the acidity of the soil. In many cases, this is beneficial because acidity allows nutrients such as phosphorus to be more available for plant growth. In other cases where the soil is already very acidic, increased acidity could be harmful, so the use of legumes may need to be combined with methods to reduce soil acidity. Legumes can also reduce the loss of nitrogen from the soil. This is important because lost nitrogen can end up as a water pollutant or greenhouse gas. Pulses also stimulate the activity of beneficial soil organisms such as earthworms, and have a positive impact on soil structure. Finally, using pulses in crop rotations can decrease pest levels, resulting in reduced need for pesticides.

Grain Legumes in Northern Great Plains: Impacts on Selected Biological Soil Processes

Published in Agronomy Journal in 2007, this peer-reviewed article summarizes how pulses affect soil biology and identifies some areas for future research. The pulses included in this summary were pea, lentil, bean, and chickpea.

Soil biology is important because microbes in the soil play a role in many of the benefits that pulses provide. Most importantly, soil microbes are responsible for the symbiotic relationship that helps pulses produce nitrogen. Pulses also release substances that affect soil microbes differently than other crops do. Pulses produce different types of amino acids and organic acids that can make soil nutrients more available to other crops. They may also increase the amount of mycorrhizae, which are a type of soil fungi that improve the uptake of water and nutrients by crops. Another type of microbe increased by pulses is endophytic rhizobia. These beneficial microbes can stimulate growth and enhance the resistance of crops to stresses such as diseases and drought.

The authors conclude that in general, pulses have a positive effect on agriculture because they add and recycle nitrogen, improve nutrient uptake, reduce greenhouse gas emissions, and decrease pest problems.

Soil microbial diversity and community structure under wheat as influenced by tillage and crop rotation

This study was published in the peer-reviewed journal, Soil Biology and Biochemistry in 1998. The study, based in northern Alberta, Canada, investigates the impact of legume-based crop rotations (field peas and red clover) and tillage management on the diversity of soil bacteria in a wheat crop.

Soil microbial diversity is important to sustainable agriculture because microbes mediate many processes that support agricultural production, including the cycling of plant nutrients. This study showed that soil microbial diversity was significantly higher when wheat was grown after field peas, compared to when wheat was grown after wheat. Tillage management also affected soil microbial diversity, with conservation (zero) tillage systems having significantly higher soil microbial diversity than conventional tillage systems.

The authors conclude that these results indicate that legume-based crop rotations and conservation tillage support diversity of soil microbial communities and may improve the sustainability of agricultural ecosystems.

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