The effect of inoculants on the growth and yield of legume crops depends on the quality of inoculant, soil properties and application techniques. 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.
Application of biofertilizers from associative nitrogen-fixing bacteria
Benefits of Biofertilizers
In general, biofertilizers from associative nitrogen-fixing bacteria could be used especially for cereal crops such as rice and wheat, but also for cash crops such as vegetables, fruits, flowers, tobacco, cotton, oilseed, tea and medicinal or herbal crops. BIO-N in the Philippines is a microbial-based fertilizer for rice, corn and other agricultural crops like tomatoes, pepper, aubergine, okra, lettuce, peach and ampalaya. It is a breakthrough technology that promises very significant impact on the country’s farmers in terms of increasing farm productivity and income as well as saving the country’s dollar reserve due to decreased importation of inorganic nitrogenous fertilizers. It is mainly composed of microorganisms that can convert the nitrogen gas into available form to sustain the nitrogen requirement of host plants. The active organisms (bacteria) were isolated from the roots of Talahib, a grass relative of sugar cane. These bacteria, once associated with the roots of rice, corn, sugar cane and some vegetable plants, can enhance their root development, growth and yield.
In China and other FNCA countries, associative nitrogen-fixing bacteria biofertilizers have increased the yields by 10–30% and reduced the use of chemical N fertilizer by 15–25%. It is reported that application of biofertilizer with associative nitrogen-fixing bacteria could enhance the maturation of crops, shorten the vegetation period by 5–10 days and improve the soil quality and soil fertility.
The benefits of biofertilizers with associative nitrogen-fixing bacteria can be seen as follows:
The liquid form is good for rice. At transplanting, immerse rice roots into liquid biofertilizer for 10–15 min before transplanting and spread on paddy soil at the regreening stage at a rate of 1.5–3.0 L per ha. For wheat, immerse the seeds into liquid biofertilizer overnight before sowing, and spread onto wheat leaves at a rate of 1.5–3.0 L per ha with water.
Solid biofertilizer is spread, band-spread and hole-applied as basal or top dressing. For leaf vegetables such as celery, spinach and cabbage, apply at a rate of 3.75–15.0 kg per ha. For fruit vegetables such as cucumber, aubergine, tomato and melon apply at a rate of 7.5 kg per ha. For root vegetables such as sweet potato, potato, ginger and garlic, apply at a rate of 3.75–15.0 kg per ha.
For fruit trees, 10–20 g, 20–30 g or 30–50 g per plant will be applied to those, respectively, with plant yield less than 50 kg, 50–100 kg and over 100 kg.
Rates of 6.25 kg per ha are applied. For those where biofertilizer with associative nitrogen-fixing bacteria is applied, the N-fertilizer should be reduced by 20–25%. Mixed application with organic manure should be encouraged because organic manure will benefit microbes.
The basal application of organic fertilizer is highly recommended to provide a whole array of other nutrients for a balancing effect. Split application of the recommended inorganic macro-elements has been found effective, e.g. second application of 14-14-14 NPK is done before tasseling.
As solid inoculant for direct-seeded rice:
As liquid inoculant for dapog bed:
Suspend the required amount of Bio-N in sufficient volume of clean water (e.g. 1 packet Bio-N to 1 gallon water) and evenly drench the seed/seedling-lined dapog bed.
As slurry for transplant seedling:
Procedures for Growing Corn using Biofertilizer Inoculated Seeds
B) Land Preparation
C) Seeds Inoculation
G) Pest Management
Generally biofertilizers in powder form are applied like organic matter onto the soil. This type is very convenient for users in the management of biofertilizers. Some biofertilizers are costly products for farmers, so their use would be restricted by the specific conditions of agronomy. Microorganisms are generally supplied by producers of biofertilizers, so it is only necessary for the users or farmers to follow the application method recommended by the manufacturers. However, the popular application method is regarded as the next procedure.
Figure 8.1: Vultivation of Phosphate Solubilizers
Two weeks before spore inoculation, the desired seedlings (e.g. oil palm, vegetable, pasture grass) are prepared in suitable containers filled with sandy loam soil.
Improvement of phosphate solubilizers:
An alternative approach for the use of phosphate-solubilizing bacteria as microbial inoculants is the use of mixed cultures or co-inoculation with other microorganisms. Evidence points to the advantage of the mixed inoculations of PGPR strains comprising phosphate-solubilizing bacteria. The effect of combined inoculation of Rhizobium, a phosphate-solubilizing Bacillus megaterium ssp. phospaticum strain-PB and a biocontrol fungus Trichoderma spp. on the growth, nutrient uptake and yield of chickpea were studied under glasshouse and field conditions. Combined inoculation of these three organisms showed increased germination, nutrient uptake, plant height, number of branches, nodulation, pea yield and total biomass of chickpea compared to either individual inoculations or an inoculated control.
On the other hand, it has been postulated that some phosphate-solubilizing bacteria behave as mycorrhiza helper bacteria. It is likely that the phosphate solubilized by the bacteria could be more efficiently taken up by the plants through a mycorrhizal pipeline between roots and surrounding soil that allows nutrient translocation from soil to plant. Considerable evidence supports the specific role of phosphate solubilization in the enhancement of plant growth by phosphate-solubilizing microorganisms. However, not all laboratory or field trials have offered positive results. Therefore, the efficiency of the inoculation varies with the soil type, specific cultivars and other parameters.
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