Nitrogen is one of the key nutrients that plants need to grow. A nitrogen deficiency in the soil in your polytunnel can make it very difficult to get a reasonable yield from the space. Understanding the soil where you live, and taking steps to improve it, is key to making the most of your polytunnel.
Nitrogen is needed by all plants but especially by leafy ones. Leafy plants will appreciate a nitrogen boost. Fortunately, it is very easy to make sure that there is sufficient nitrogen in your soil to allow such plants to thrive.
In a no-dig system, which takes care of the soil ecosystem, mulches added on top of the growing surface will allow the balance of the system to be maintained. Mulches that are high in nitrogen can help boost nitrogen levels in the soil below and increase the amount of nitrogen that is available for the uptake of nearby plants.
Nitrogen rich mulches include grass clippings from a lawn, wilted nettles and a variety of green waste that has been partially composted. Each of these are fantastic when laid as a spring/summer mulch around leafy vegetables and other nitrogen hungry plants.
Another way to add nitrogen to the soil is with nitrogen-fixing plants. Nitrogen fixers are plants that co-operate with nitrogen fixing bacteria on their root nodules to take nitrogen from the air and put it into the soil in a form that is useable by other plants in the vicinity, either at the same time or next time round in a crop rotation system.
The best way to ensure a stable supply of nitrogen in the soil is to find space for these nitrogen fixers in your polytunnel. Beans and legumes, for example, should be regularly rotated around all the annual vegetable growing areas in your polytunnel to ensure they fix nitrogen in all the areas. You can also plant permanent nitrogen fixers in polyculture planting schemes.
Take the measures described above and, all else being well, you should discover that you are never faced with a nitrogen deficiency in your polytunnel. This will mean that the soil remains healthy and fertile and your growing efforts are rewarded with the most satisfying of yields from your polytunnel.