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2.4 APPLICATION OF BIOFERTILIZERS ON DRYLAND LEGUMES
The biofertilizer used for legume crops is rhizobial.
Generally, inoculants should be used according to the specification on the package and when a legume is introduced into a new area or when the legume is known to have a nodulation problem. The main purpose of inoculation is to nodulate the host legume with a selected rhizobial strain. The inoculant should be of good quality at the time of application.
Commonly, two application methods are used in the inoculation of rhizobial biofertilizers to legumes. This is direct inoculation, where the inoculant is placed in direct contact with the seeds (seed-applied inoculant), and indirect inoculation, whereby the inoculant is placed alongside or beneath the seeds (soil-applied inoculant).
Inoculant is applied to seeds in the following ways:
a) Dusting: With this method, the inoculant is mixed with the dry seeds directly. This may lead to poor adherence of rhizobia to the seeds; the method is least effective.
b) Slurry: The inoculant can be mixed with wetted seeds, or diluted with water and some stickers, e.g. 25% solution of molasses or 1% milk powder. In some cases, gum Arabic, sucrose of methyl ethyl cellulose can be used as stickers.
c) Seed coating: The inoculant can be made into slurry and mixed with the seeds. The seeds are then coated with finely ground lime, clay, rock phosphate, charcoal, dolomite, calcium carbonate or talc. The method has several advantages, such as protection of rhizobia against low pH soil, desiccation, acidic fertilizers, fungicides or insecticides.
In the indirect application method, the inoculant is applied to the soil beneath or alongside the seeds. The method is used when seeds are treated with fungicide or insecticide, and when a high amount of inoculant is needed to outcompete the indigenous rhizobial population. The simplest inoculation is to prepare the liquid formulation of the inoculant and spray to the soil or directly over the seeds after placement. In this case, a high amount of inoculant is needed. Some disadvantages of this method include loss of viability of rhizobia, short storage period and difficulty in the distribution of inoculant.