Nitrogen is the mineral that plants need to grow tall and green. It is one of the three primary minerals in fertilizer. As plants grow, they strip nitrogen from the soil. Although synthetic fertilizers containing nitrogen are available for purchase at many garden centers, organic farmers say these fertilizers can run off into the water supply and pollute the environment. Nitrogen runoff can create algae bloom in major waterways. But there are several organic methods to increase nitrogen in soil.
Rotate your garden plants with a crop of alfalfa, soybeans, pole beans or other legumes. Legume plants such as soy beans pull atmospheric nitrogen from the air and place it back into the soil. At the end of the year, the leftover plant material may be mulched into the garden or used to create compost to add even more nitrogen to the soil.
Plant a cover crop of clover during cooler months. Clover will prevent invasive weed plants from establishing a foothold. In spring, plow these crops into your garden soil with a rototiller. Once the crop is plowed into your soil, it will decompose and add more nitrogen to the soil.
Create compost by layering green organic materials that are filled with nitrogen such as peat moss, manure, grass clippings, clover, green plant wastes such as legume stalks and kitchen wastes with brown, carbon-filled compost material such as dead leaves, dead plant stalks and straw. The compost pile should be at least 3-foot square and the brown layers should be twice as thick as the green layers. All waste particles should be cut to 1 inch in size. Wet the compost pile so it is as damp as a wrung-out sponge all the way through. Turn the compost pile weekly to help it decompose until all particles of the pile are the consistency of fine loam.
Spread a 4-inch layer of compost and peat moss over your plowed soil. Compost and peat moss are nitrogen-rich organic soil amendments that are good alternatives to chemical fertilizer. Mix these amendments into the soil to a depth of 12 inches with a rototiller to improve the nutrient content, aeration and soil structure of soils.