Nitrogen: Plant Growth

Your plants need nitrogen for green, leafy growth and stalk development. Nitrogen exists largely as an element in the atmosphere, but also in the soil and oceans. Converting nitrogen from the atmosphere to a form available to plants requires a microbial process called nitrogen fixation.

When a more immediate source of nitrogen is required, fertilization with organic or synthetic fertilizers provides a source of nitrogen to plants. Understanding the nitrogen cycle, the nitrogen fixing process and soil amendment guidelines will help you maintain a healthy level of nitrogen in the garden.

Nitrogen Cycle

Nitrogen begins as a gas in the atmosphere and is transferred to soil through lightning and microbial processes. Though plentiful, it cannot be used by plants until converted to nitrates through decomposing plant material and the nitrogen fixation process provided by legumes. Once converted to nitrates, plants, especially green leafy plants, use the element nitrogen for vigorous vegetative growth. When plants decompose, they return nitrogen back to the soil.

Nitrogen Fertilization

Amend nitrogen-deficient garden soil with slow-release, organic forms of nitrogen fertilizer. Slow-release nitrogen fertilization provides the element at a rate plants can take up over the course of the growing season. Blood meal, feather meal and composted dairy manure are slow-release fertilizers.

If plants are yellow, light-green or stunted, top-dress with grass clippings or compost.

After the growing season is finished, plow under remaining plant leaves, stalks and vines. Seed the field with alfalfa, field peas, red clover or soybeans for nitrogen fixation while your garden waits to be re-planted. Plow the crop under three weeks prior to the next planting season for maximum benefit.

When applying non-organic, quick-release fertilizers, research the amount of nitrogen and other elements needed for your crop and apply the fertilizer at the rate specified for that crop in the instructions. Do not apply more fertilizer than directed as over-fertilization with nitrogen directs the plant’s energy toward leaf growth at the expense of fruit and vegetable production. Tomatoes, for example, do not require much nitrogen. If excessively fertilized with nitrogen, they will grow tall and bushy, but will not produce many tomatoes. Squash, corn and lettuce are heavy nitrogen feeders, however. For strong vines, stalks and leaves, dig 6 inches of composted cow manure into the soil three weeks before planting these vegetables.

Nitrogen Run-off

Nitrogen is water soluble and easily leaches out of soil. Avoid adding nitrogen to the soil before heavy rains and never add more nitrogen to the soil than is required by the crop you are growing.