Table of Contents

  1. Which Cover Crops Fix Nitrogen?
  2. Ensuring the Nitrogen Incorporates Into Soil

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Cover crops are a great way to fix nitrogen, acting as an input for nitrogen in your garden or farm system.

For a quick refresher on what nitrogen fixation is and how the process works, check out Nitrogen Fixation and then head back here.

The TL;DR is that some specific bacteria can pull nitrogen from the air, and some plants are adapted to provide food and housing for these bacteria on their roots in exchange for this service.

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The end result is that the ecosystem has a natural input from nitrogen, pulling it from the atmosphere and turning it into a usable solid form.

Which Cover Crops Fix Nitrogen?

The following list includes many common cover crops which fix nitrogen. Most are legumes.

Their relative N-fixation amounts per acre are listed for comparison, and assume optimal conditions. Cover crops with the highest nitrogen-fixing potential are listed first.

Many require inoculation with rhizobium bacteria with which they synergize - so be sure your cover crop seed comes pre-inoculated (often labeled "nitro-coated") or that you inoculate it yourself prior to planting.

Cover Crop Avg. N Fixed
(lbs/acre)		 Season Notes
Alfalfa 150-200 Cool/Warm Perennial, drought-tolerant; second year+ for high fixation
Velvet Bean 150 Warm Fast-growing tropical legume
Sunn Hemp 125 Warm Fast N-fixer; not frost-tolerant
Lablab 120 Warm Vigorous warm-season legume; drought-tolerant
Fava Beans 115 Cool Bulky biomass, easy to terminate
Common Vetch 110 Cool Similar to hairy vetch, easier to terminate
Sweet Clover 110 Cool/Warm Deep taproot, breaks hardpan
Hairy Vetch 100-170 Cool Winter-hardy, late maturing; highly variable based on biomass
Cowpeas 100-150 Warm Excellent in hot climates, drought-tolerant
Chickling Vetch 105 Cool Good drought resilience
Tepary Bean 100-120 Warm Extremely drought-tolerant; native to Southwest; short season
Berseem Clover 100 Cool Good regrowth, high biomass
Balansa Clover 100 Cool Tolerates waterlogged soils well
Sainfoin 100 Cool Non-bloating legume for pastures
Arrowleaf Clover 95 Cool Late spring growth; good reseeding
Field Peas 90-150 Cool Great biomass and weed suppression
White Clover 80-200 Cool/Warm Low-growing; great in pastures; highly variable
Persian Clover 80 Cool Tolerates mowing well
Red Clover 75-200 Cool/Warm Biennial/perennial; frost-hardy; high fixation when well-established
Mung Bean 75-80 Warm Short season; drought-tolerant; low N if harvested for grain
Subterranean Clover 75 Cool Self-reseeding annual
Black Medic 75 Cool Low-growing, good for ground cover
Lespedeza 75 Warm Good for degraded land
Desmodium 70 Warm Often intercropped with grasses
Fenugreek 70 Cool/Warm Aromatic legume, drought tolerant, shorter growing season than alfalfa
Sesbania 60-150 Warm Fast-growing annual; reaches 8-12 ft; good biomass producer
Alsike Clover 60-120 Cool Tolerates wet, acidic soils; biennial; cold-hardy
Birdsfoot Trefoil 60 Cool Slow to establish but persistent
Crimson Clover 50-150 Cool/Warm Early maturing; good for rotations; highly variable
Partridge Pea 50 Warm Native pollinator support
Soybean 30-50 Warm Primarily grown for grain; limited N credit for following crops

Ensuring the Nitrogen Incorporates Into Soil

Once you've grow nitrogen-fixing cover crops, the nitrogen will be locked up in the plants. You need to ensure that the plants are incorporated into your soil in order to gain the benefits of the nitrogen.

A few ways to accomplish this:

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That's all for now, thanks for reading!

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