Ideal Nitrogen Percentage for Soil

Soil Tests

• Nitrogen enters and exits soil as a natural part of the nitrogen cycle. Atmospheric nitrogen enters soils through soil surface gas exchanges and through precipitation. Organic matter -- in the form of bacteria, fungi and insects -- also contribute to soil's nitrogen content. These living organisms transform organic nitrogen into plant-accessible inorganic nitrogen. Compost, manure and fertilizers also increase the amount of nitrogen present in soil. Before adding fertilizers to your soil, submit soil samples to a local university cooperative extension. It is important to determine the baseline amount of nitrogen present in your soil before adding more nitrogen. Too much nitrogen disrupts the existing nitrogen cycle and can damage your soil structure for years.

Humus

• The organic matter present in soil, to include microorganisms, is called humus. Well-balanced humus is made up of 5 percent nitrogen and 45 to 55 percent carbon to form a 12-to-1 ratio of carbon to nitrogen. Soils that contain less organic matter also contain less nitrogen. Incorporating compost into your soil annually is one way to encourage healthy nitrogen percentages. Fertilizers add soluble nitrogen to soil, but soluble nitrogen is easily leached from soil through precipitation and aggressive uptake by root systems and microorganisms. The nitrogen found in humus is slowly released through the decomposition of organic matter.

Growth Cycle

• Plants require different amounts of macronutrients during different stages of their growth cycle. The major nutrients -- potassium, phosphorous and nitrogen -- each offer a maturing plant different growth opportunities. Phosphorous helps protect plants from disease while potassium encourages root development. Both nutrients encourage flowering and fruiting. Nitrogen encourages leafy shoot growth at the expense of flowering and fruiting. High nitrogen fertilizers are often used for lawns or other foliage plants.

Fertilizers

• Soil test results include recommended fertilizer percentages. These recommendations are meant to bring your soil into the best nutrient range possible. Fertilizer recommendations are given using ratios and percentages, and fertilizers are sold using labels listing the ratios of ingredients. The first number in the ratio indicates the percentage of nitrogen present in the fertilizer, the second number is the amount of phosphorous and the last number the amount of potassium. Complete fertilizers include all of these nutrients. Incomplete fertilizers contain only one or two of these nutrients. Balanced fertilizers contain the same amount of each ingredient. By following the recommendations of your soil test and applying the correct amount of supplemental nitrogen, you will bring your soil to its ideal nitrogen percentage.