An Introduction to Inoculants
Nitrogen fixation is one of the most critical components for producing higher yields in
soybeans, peas, alfalfa, peanuts and other legumes. It is critical for producers to
understand how and why this process occurs so that they may make informed
decisions about the brand and formulation of inoculant they choose. This booklet is
aimed at providing that information.
Inoculant use continues to climb in North America. This is partially driven by new
formulations and production practices that make inoculation more responsive and
beneficial than ever. Research by EMD Crop BioScience has produced new formulations of
inoculants (such as Cell-Tech® and LIFTTM
brand liquids). They provide higher numbers of specially selected strains of Rhizobia
bacteria, plus applications that make inoculation easier and more convenient. In many
areas, nitrogen is the major nutrient limiting yields. Using inoculants is far less
expensive than nitrogen fertilizer applications, and it avoids run-off concerns.
How nitrogen fixation works
Nitrogen fixation is the process of converting atmospheric nitrogen into a usable form
for the plant. Nitrogen-fixing bacteria known as Rhizobia are introduced into the soil
either directly or by applying them to the seed. When the seed germinates, the
bacteria invade the root hairs of the seedling and begin to multiply. Nodules,
which house the bacteria, form on the roots. These first nodules can take about
four weeks to fully develop. The symbiotic relationship occurs as the plant supplies
the Rhizobia with photosynthate - a food source the bacteria uses for energy - and
the bacteria convert nitrogen gas (N2) to ammonia nitrogen (NH3) for the host. This
biochemical conversion process makes unusable atmospheric nitrogen available to the
legume plant in a usable form. The legume is then able to translocate the usable
nitrogen through its vascular system to its leafy tissue and seed. The amount of
nitrogen fixed varies by crop and conditions, but in some instances can go as high as
90 percent of what the plant needs. If the nitrogen cannot be derived from other
sources, yield potential may be decreased.
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1. Rhizobia multiply in root zone and invade root hairs.
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3. Root cells and Rhizobia multiply to form nodule.
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2. Rhizobia follow infection thread, then the infection thread invades cells in root.
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4. Rhizobia in nodule make atmospheric nitrogen available to the plant.
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Discovering the relationship
In 1886 Hellriegel and Wilfarth, two German scientists, discovered that a symbiotic relationship
existed between Rhizobia bacteria and legume plants within the nodules of the legume root system.
The Rhizobia bacteria were isolated, and in 1890 two other German scientists, Nobbe and
Hiltner, demonstrated the advantage of adding pure bacteria with the seed at planting. This led
to the beginnings of the commercial inoculant industry and the establishment of EMD Crop BioScience®
in 1898. EMD Crop BioScience is currently the oldest and largest producer of Rhizobia bacteria
inoculants in the world.
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