This guide explains how to correct nitrogen deficiency in Soil using natural sources of nitrogen for plants. Scroll to the bottom for two simple homemade organic nitrogen fertilizer recipes.
Nitrogen is the mineral that a plant needs in the greatest amounts. It is the principal constituent of amino acids and a healthy plant will contain 3-4 percent nitrogen in non-root tissues.
Long before the scientific discovery of the element nitrogen and its role in plant nutrition, farmers noticed that planting legume crops like clover made soil fertile. Uniquely among plants, legumes produce their own nitrogen and replenish the nitrogen content of the soil they grow in. This is thanks to a bacteria (Rhizobiaceae, α-Proteobacteria) that resides in their roots.
Some plants can 'fix' nitrogen from the air through microbes that exist on their roots.
Although nitrogen gas is 80 percent of Earth's atmosphere, man-made nitrogen was rare before the beginning of the 19th century. This was until the invention of the Haber-Bosch process in the early 20th century - a method to obtain nitrogen from the air.
Cheap synthetic nitrogen fueled the 20th century revolution in global food production. Yet this created a huge ecological crisis. Synthetic nitrogen run-off from agricultural land into the wider environment constitutes a major pollution problem.
Rather than buying synthetic brands of nitrogen fertilizer, made your own organic version at home. Obtaining nitrogen from organic sources means that you won't be introducing surplus nitrogen into the ecosystem.
What is in fertilizers?
All plant fertilizers contain nitrogen, phosphorus, and potassium. These are the macronutrients, the elements found in the largest quantities in plants. Different types of fertilizer contain these macronutrients in different amounts and ratios.
Nitrogen (N) is critical in chlorophyll and amino acid building. It aids leaf production. A nitrogen deficient plant will send the nutrient to young shoots first and then to mature leaves. Dying mature leaves can be a sign that your plant needs nitrogen.
Phosphorus (P) is involved in energy transfers for cell metabolism. It comprises the structure of cell membranes and nucleic acids. Stunting, purple leaves, and lesions are signs of deficiency.
Potassium (K) regulates stomata (small pores on the leaves that allow gases to move in and out of plant cells), maintains turgor (water pressure in the plant that keeps it upright), and osmotic equilibrium (the transfer of nutrients in the plant from areas of high to low density). Leaf lesions are a sign of potassium deficiency, with mature leaves dying first. Potassium is particularly crucial in fruit growth.
While plants also require thirteen other elements in smaller quantities, these micronutrients are usually found in sufficient quantities within the soil. Plants need all three macronutrients and thirteen micronutrients to carry out essential physiological maintenance and achieve growth.
How do plants eat?
All nutrients are taken up from the soil by the root and transported through the plant.
Nutrients are moved through the plant through three mechanisms: transpiration, root pressure that pushes water and nutrient ions upwards, and the source-sink phenomenon, which draws water and ions from less active parts of the plant to places that are actively growing, such as shoots or fruit.
What are nitrogen-rich fertilizers?
Nitrogen-rich fertilizers contain a higher ratio of nitrogen compared to the two other macronutrients (phosphorus and potassium). You can identify commercial brands of nitrogen-rich fertilizer by looking for nutrient percentages like 10-5-5, which means that the macronutrient content is 10 % nitrogen, 5 % phosphorus, and 5 % potassium.
The ratio figures you find on commercial fertilizer brands are called ‘NPK’ ratios. Each number indicates the percentage of nitrogen, phosphorus, and potassium respectively in the fertilizer. The rest of the product is filler material that does not impact the plant.
A 5-5-5, 10-10-10, or 12-12-12 fertilizer contains nutrients in a 1:1:1 ratio to one another. All three of these NPK ratios indicate a balanced fertilizer, containing equal amounts of each macronutrient. The only difference between a 12-12-12 fertilizer and a 5-5-5 fertilizer would be that you need to use less of a 12-12-12 product than a 5-5-5 product since the first contains 7 percent more nitrogen, phosphorus, and potassium.
Fertilizers with lower macronutrient percentage figures should be used on smaller plants and those with higher macronutrient percentage figures should be used on larger ones.
Homemade, organic fertilizer recipes tend to contain less concentrated amounts of the target nutrients than commercial, chemically synthesized ones. This lessens the chance of killing plants with over-fertilizing. It is also more environmentally sound, as there is less chance of releasing excess fertilizer into the wild.
When to use nitrogen fertilizer
Because nitrogen builds amino acids, they are important in developing cell membranes and chlorophyll, which is essential for photosynthesis. Nitrogen is great for leafy vegetables like kale, lettuce, and spinach in their growth season. Beets, brussels sprouts, broccoli, cabbage, and cauliflower also need high levels of nitrogen. Cucumber, carrots, fava beans, peas, radish, parsnip, and turnip do not.
Like all fertilizers, nitrogen-rich fertilizers should only be used in the immediate lead-up to and during a plant's growth season.
Signs of nitrogen deficiencies are yellow and withering leaves. If your Basil leaves are turning black, it may indicate a nitrogen deficiency in the soil.
Homemade nitrogen fertilizer recipes
The following recipes will produce fertilizers are high in nitrogen with little of the two other macronutrients - phosphorus and potassium. They should be used when the soil is deficient only in nitrogen.
Recipe for homemade nitrogen fertilizer #1: Urea and grass
This is the easiest fertilizer to make at home - both key ingredients are readily available: grass and urine! Urine is an overlooked nutrient source that is too often wasted.
Don't waste your grass clippings either - they are a good source of nitrogen, with an NPK ratio of 4:2:1 (4 % nitrogen, 2 % potassium, 1 % phosphorus).
Fill a 5 gallon bucket with grass clippings. Fill the bucket with water and leave for 3 days.
Mix 1/4 cup of Epsom salt with two cups of urine. Add this to the grass clippings steeped in water.
Strain the liquid and dilute it by half with water. Pour into a bottle ready to apply to the soil.
Recipe for homemade nitrogen fertilizer #2
Add two cups of used coffee grounds to 5 gallons of water. Leave overnight, strain the liquid into a bottle and add to the soil or spray onto your plant's leaves. For plants that like a lower acid content, used decaffeinated coffee grounds.