IN OUR supermarkets legumes, or pulses, such as peanut butter and baked beans tend to receive little attention while chickpeas, kidney beans and lentils can, at times, be hard to find.
This is a sad fact because world agriculture really needs to get more legumes growing to help stop global soil degradation, increase food production and meet the protein demands of our rapidly-increasing population.
Legumes contain the highest levels of protein among the seeds we eat and perform what is known as nitrogen fixation. As we know plants need nitrogen to help the process of photosynthesis. It is also a building block of DNA and cells in plants.
Most plants receive their nitrogen from the soil but legumes take their nitrogen from the air and any excess finishes up in the soil for other plants to use. For example a crop of wheat takes up nitrogen from the soil but a crop of peas will put it back in.
Traditionally farmers used this to their advantage by rotating their crops, and so recharged the soil with both organic matter and nitrogen. But today farmers tend to rely on petroleum-derived urea, and have taken legumes such as clover out of their pasture plantings.
Blind Freddy can see the huge increases in productivity that synthetic nitrogen fertilisers can produce in crops, but the disadvantages are quite frightening.
It becomes more expensive because, as the overworked soil becomes less fertile, it needs more of this finite petroleum resource.
Runoff from rain and irrigation carries nitrogen into streams where it pollutes and promotes algal blooms.
The breakdown of these nitrogenous fertilisers creates nitrous oxide, a greenhouse gas, which is about 300 times more damaging to the ozone layer than carbon dioxide.
Grain crops such as wheat, maize and barley do not add organic matter to the soil which is one of the reasons the world suffers from serious soil degradation.
To me it makes sense to put legume crops back into the planting cycle to receive free nitrogen and organic matter.
The protein advantage of legumes is shown by the fact that 100gms of wheat has about 14gms of protein whereas the same amount of chickpeas has 19gms.
The world demand for protein is increasing at lightening speed, so we must be prepared to supply protein by much more environmentally-friendly and less resource-heavy production than we do today by aiming towards plant-derived protein.
Suburban gardeners can gain these advantages by growing peas and beans in their vegetable gardens and now is a good time to do it. A rich, well-drained soil in a sunny position is perfect for legumes.
After harvesting the peas and beans, dig the trash into the garden to enrich the soil for the following crop of nitrogen-greedy, leafy vegetables.
- Les Hodge is a gardening columnist for The Advocate.