This week we will talk about how the planting of legumes helps fix nitrogen to your soil.
Why do I need to fix nitrogen to my soil?
Nitrogen is an essential nutrient that plants need to grow. During a season of growth, plants will be consuming this nutrient so, at the end of the season, you need to replace it ahead of your next crop.
What will fix nitrogen to my soil?
Peas, beans, broad beans, buckwheat, lupins, vetch, and clover all fix nitrogen to the soil and are sometimes grown as cover crops or green manure crops in over-wintering beds.
The legume family contain symbiotic bacteria called rhizobia in the nodes of their root system. These produce nitrogen that helps the plants to grow and also helps them to compete with other plants. When the plant is spent, the fixed nitrogen is then released into the soil making this essential nutrient available to follow-on plantings, along with nearby plants, and in turn helps to fertilise the soil.
We could get really technical here however, sticking true to my principles of keeping it simple, I will explain only the basics to you the average gardener.
How does it work – what do I need to know?
Legumes release organic compounds from their roots which attract rhizobia to them. The rhizobia is attracted to the root hairs of your plants and the hairs curl around the rhizobia which create a pathway for it to travel into the root cells.
Rhizobia is an important bacteria in the soil that has the ability to make the nitrogen that is in our atmosphere available to our plants. In exchange for the nitrogen, the plant provides carbohydrates to the bacteria. They form nodules attached to the roots of your legumes.
The nitrogen fixing bacteria can also help to increase the soil fertility for all plants. This is why it is so good to do your crop rotation with any of the above plants. After harvest, you can leave your roots in the soil and, when they break down, they provide nitrogen to the next crop.
Nitrogen top tip #1: If you pull your plants out, be sure to cut off the roots and dig back in otherwise you will lose all the valuable nitrogen from these plants.
Nitrogen top tip #2: It is always good to interplant with other crops – even in between rows – as this will help keep your soil restored of nitrogen and enable you to have a healthy garden without your plants stressing out.
Nitrogen top tip #3: Please remember that all legumes also like plentiful supplies of phosphorus and calcium, which can be added with the addition of lime, rock phosphate or gypsum. So if your crop didn’t do so well last year, take these factors into account before your late spring / summer sowing.
With the daylight hours getting longer next week, we will talk about preparing your soil for spring/summer. To dig or not to dig…? That is the question!