Agriculture Business Week

Legumes are the richest and cheapest common source of protein among all foods of plant origin. Protein found in legumes is a cheap substitute for fish, chicken, pork, and other meats. Aside from being an important food in the human diet, legumes are also good supplementary feed for livestock and poultry.

Legumes-soybean, mungbean, peanut, string bean, winged bean, to name a few – are special kinds of plants. They have the ability to hide bacteria in their roots, which form nodules (numerous rounded masses in the roots). The bacteria present in these nodules catch nitrogen from the air and transform it into usable form and supply it to the soil to be used by the next crop.

“Though nitrogen is abundant in nature – cycling between the atmosphere, soil and living organisms-it is only directly available to plants when converted through biological or industrial processes to certain forms, primarily ammonium and nitrate,” explains Lindsay Watkins, seed bank manager of the Florida-based Educational Concerns for Hunger Organization (ECHO).

Some nitrogen is made available to plant through the decay of existing soil organic matter (example: manures and plant residues) or residues of the current crop. A small amount of atmospheric nitrogen is also “fixed” and converted to nitrate through lightning. Generally, these methods are not sufficient to replenish the nitrogen taken up by the crop and removed with the harvest.

“Adequate replacement of plant-available nitrogen in the soil, then, is accomplished by applying fertilizer (expensive inorganic chemicals, manure, etc.) and through biological nitrogen fixation.”

Nitrogen fixation in the soil is primarily accomplished through a symbiotic relationship between plants in the legume family and a soil bacterium called rhizobium. This microorganism interacts with the roots of leguminous plants to produce nitrogen which will naturally fertilize the plant and build soil fertility.

“If the nitrogen-fixing bacteria are not present in the soil, legumes will have to depend much on soil nitrogen. As such, the soil is depleted of its nitrogen,” explains Roy C. Alimoane, director of the Mindanao Baptist Rural Life Center (MBRLC) Foundation, Inc. in Kinuskusan, Bansalan, Davao del Sur. Both ECHO and MBRLC are nonprofit, Christian organizations that help poor people in industrialized countries to grow food using science and technology

According to Watkins, a legume growing in its native habitat is likely to have the appropriate bacteria present in the soil. “If nodules are present on the roots, especially along the taproot near the crown, and if the nodules are pink or red inside, then an appropriate bacterial strain is living in the soil and actively fixing nitrogen in symbiosis with that legume,” she says..

If the nitrogen-fixing bacteria are not present in the soil, then it is necessary to introduce them into the soil where legumes are to be planted. This is made possible through a procedure called inoculation.

There are several benefits a farmer can get when he inoculates the seeds of legumes before- planting. The most obvious is the reduced need for fertilizer application (specifically inorganic nitrogen). Also, nitrogen fixed by bacteria is not as quickly leached from the soil as is applied nitrogen, resulting in a more stable nitrogen pool.

Soil quality is also enhanced by inoculation, which fosters microbe diversity and residual nitrogen buildup over time. Finally, forage quality is improved when legumes are inoculated, since the increase in nitrogen levels promotes an increase in the legume’s protein content.

But when should a farmer need to inoculate the legume seeds before planting? For one, when the legume to be planted has not been grown previously in the area. For another, if the legume grown recently on the land lacked good nodulation. Another is when a legume is to be planted on land currently planted in non-leguminous crop like corn, ampalaya, and tomato, among others. Inoculation is also needed when the legume to be planted is a species widely different from those which were grown previously on the land.

Alimoane says there are two ways of inoculating legume seeds. The first is done this way: Put your seeds in a large container and moisten them with water. Sprinkle with the inoculant and stir to ensure that it evenly sticks to the seeds.

“Inoculation should be done in shade within one hour before planting,” Alimoane instructs. “Do not expose inoculated seeds directly to sunlight to avoid killing the nitrogen-fixing bacteria.”

This is the second method: Well-pulverized soil from a field recently planted to same leguminous plant, which is positively known to have produced plenty of root nodules, should be mixed thoroughly with the seeds to be planted. The seeds are to be planted as soon as possible after they are inoculated.

Inoculants can be bought from the Bureau of Plant Industry office or at the Bureau of Soils and Water Management. They can also be purchased at agricultural stores. “Every type of legume has its own type of inoculant,” reminds Alimoane. “Be sure to buy the right inoculant for the legume you intend to plant.”

Farmers can see the effect of inoculation two to three weeks after planting. “You can pull up some of your plants and see the nodules or `bumps’ attached to the roots,” Alimoane says. “These are where the nitrogen-fixing bacteria live.”

But. there are instances when inoculation may not be successful at all. For one, the inoculant used may not be the right inoculant. As stated earlier, it is important to match the legume species to the appropriate bacteria that can effectively nodulate the plant.

Another reason might be is the poor soil condition. Rhizobialbacteria.grow best at a temperature of 82°F-86°F. If soil temperatures are too high, especially during the establishment, the bacteria will not survive. A pH of 6-7 is optimal for rhizobial growth, while acidic conditions inhibit growth.

It might be that the inoculant you used was already expired. Inoculant is a biological product, meaning it contains living organisms. Consequently it does not have a long shelf life. So check for the expiration date written on the package when buying inoculant. Even if the expiration is still current, poor storage (it should be stored in a cool and dark place) and handling (direct exposure to sunlight) may have killed the bacteria.

By Henrylito D. Tacio