For: Saturday, Jan.17, 2004
By: Daniel E. Mullins
Extension Horticulture Agent
Inoculate Legume Seed for Best Results
Most gardeners grow legumes and these are special plants. There are over six hundred genera and twelve hundred species within the Leguminosae family. Some commonly grown vegetables and ornamentals are found here including bean, pea, clover, peanut, Lespedeza, Cassia, Redbud, Mimosa, Wisteria, Lupine and Parkinsonia.
Members of this large plant family have the unusual ability to “make” their own nitrogen. Actually, rather than making nitrogen, they have a symbiotic relationship with a nitrogen fixing bacteria that lives on their roots.
The specialized bacteria, after invading the roots, form nodules which are small warty appearing growths. The bacteria, once established, utilize atmospheric nitrogen in their metabolism, while converting it into a form that the plant can use. It is possible for as much as 150 to 250 pounds of nitrogen per acre to be fixed in the nodules of some legumes during a single season.
Sounds great doesn’t it! So, if you are waiting for the other spade to drop, here it is. In order for this nitrogen fixation to take place, certain bacteria must be present in your soil.
Inoculation is the only way to be certain that these specialized bacteria are present. Commercial inoculants are sometimes available and can be bought at the same time as seed. Make certain that a particular product is for that species of plant. Some species require a certain inoculant, while others work on a wide range of legumes. Follow label directions when mixing inoculants with seed.
Some small-seeded legume seeds are sold that were pre-inoculated. These have been coated with a substance that contains the appropriate bacteria. Though this might appear to be an easy way to be certain of inoculation, the microorganisms don’t generally live for very long when used as part of the seed coating. In this case, it is very important that the product be fresh.
In many cases, the nitrogen fixing bacteria are already in your soil. It is just a matter of making sure. Check the root system of several plants. Nodules located on the major roots indicate the presence of the desired bacteria. Healthy nodules will be red or pink inside.
Soils that have successfully grown legumes may harbor enough nodule bacteria. However, on land where legumes have not been grown before or where crops have been rotated, inoculation of the seed is always good insurance.
Question of the Week: I have recently planted some trees and plan to mulch around them. Can pine straw be used for mulch?
Answer: Pine straw or pine needles make excellent mulch. Be sure to use enough that, when it settles, there is a 2 to 3 inch layer on the soil surface. Once the job is complete, pull the mulch back a couple of inches from the base of each tree. If left piled in contact with the trunk, mulch can hold too much moisture on the bark surface and lead to crown rot.