How To Inoculate Legume Cover Crops For Better Nitrogen In Backyard Soil

Legumes such as peas and beans act as natural nitrogen fixers by creating a symbiotic relationship with bacteria found in their roots. Rhizobia-containing bacteria create nodules on legume roots that have pinkish or red interiors to indicate they’re effectively fixing atmospheric nitrogen.

To maximize nitrogen fixing, legume cover crops must be inoculated with appropriate rhizobia strains. Commercial preparations of live rhizobia come as powders or peat or humus mixes that coat legume seeds.

Inoculation

Legumes have the unique capability of “fixing” atmospheric nitrogen gas, turning it into forms plants can uptake. They do this by working in concert with specific bacteria known as Rhizobacteria in root nodules to provide food for these bacteria that in turn provide nitrogen for plants’ uptake – turning nitrogen into a renewable resource compared with non-renewable sources like phosphorus, potassium and calcium which cannot regenerate as easily.

As well as adding nitrogen to a garden, legume cover crops also help prevent erosion, build soil organic matter levels and attract beneficial insects, while supporting soil microbiology activity. Varieties include sweet clover, crimson clover and hairy vetch for legume cover crop varieties.

To maximize nitrogen fixation, for optimal legume cover crop seeds at planting time use an inoculant such as Rhizobium which can be found at most local nurseries and comes as a powder that you sprinkle onto each seed before sowing. Each variety of legume is specifically tailored to work with this inoculant.

Sowing

Cover crops offer numerous advantages to any farm system, but selecting the correct species or mix can bring particular advantages. When considering cover crop options for your farm system, be sure to set realistic goals before choosing species such as winter hardy grasses (like cereal rye, wheat or barley) or nitrogen fixing legumes such as crimson clover, Austrian winter pea or hairy vetch that fix nitrogen.

Legumes form an intimate partnership with Rhizobia bacteria that help them capture and make available nitrogen to their host plant. Their roots produce nodules which enclose these Rhizobia colonies while providing shelter. Once in turn, these Rhizobia supply nitrogen directly back to the legume.

Start small when beginning to cover your fields – begin with areas or field segments most at risk of erosion and nitrogen leaching – paying close attention to weed control, tillage practices and any herbicide seed treatments necessary. Cover crops should ideally be planted during autumn for adequate biomass growth and overwintering.

Fertilization

Under ideal conditions, legume cover crops can fix up to 80 percent of the nitrogen they take in from their soil environment, yet still remove organic N from it – especially when ploughed under or disced aggressively (especially in warmer climates) the remaining N is vulnerable to gaseous loss as ammonia or nitrate emissions occur.

Legumes use their own rhizobial bacteria to fix nitrogen, but many factors can interfere with this natural process. To maximize efficiency of symbiosis between legumes and bacteria, make sure that an appropriate inoculant for each legume species being grown is used, with soil pH between 6.0 to 7.0 ideal.

Cool-season legumes like field peas and fava beans, as well as summer annuals like buckwheat, provide an effective means of balancing fixed nitrogen releases with quick cash crop development. Tillage or roller crimping the crop can speed decomposition and mineralization while plowing or incorporating during wet conditions can prevent loss of nitrogen-fixing organisms such as bacteria. For enhanced results, combine legumes with grasses like rye or oats for further benefits.

Harvest

Legumes capture nitrogen from the atmosphere and make it available to plants through natural means, significantly reducing chemical fertilizer needs. They do this through an association with rhizobia bacteria that form nodules on legume roots that fix nitrogen for carbon nutrients from plants in exchange.

Most gardeners employ both legume and nonlegume cover crops in their gardens, with legumes such as crimson clover, field peas, and hairy vetch being prominent examples of legume cover crops. These cover crops can be planted either fall or winter before being tilled into the soil in early spring; full bloom should be terminated to optimize nitrogen-fixation.

Nonlegume cover crops include annual grasses like oats, barley and rye which scavenge nutrients from the soil while at the same time acting to break up erosion. When cultivating nonlegume cover crops for recycling of nutrients it’s essential to take note of their regrowth habits and any potential interference they could pose to future cash crops.