Biofertilizers in Kerala
Biofertilizer is a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonizes the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. Biofertilizers add nutrients through the natural processes of nitrogen fixation , solubilizing phosphorus, and stimulating plant growth through the synthesis of growth promoting substances. Biofertilizers can be expected to reduce the use of chemical fertilizers and pesticides. The microorganisms in biofertilizers restore the soil's natural nutrient cycle and build soil organic matter. Through the use of biofertilizers, healthy plants can be grown while enhancing the sustainability and the health of soil. Since they play several roles, a preferred scientific term for such beneficial bacteria is plant-growth promoting rhizobacteria (PGPR). Therefore, they are extremely advantageous in enriching the soil fertility and fulfilling the plant nutrient requirements by supplying the organic nutrients through microorganism and their byproduct. Hence, biofertilizers do not contain any chemicals which are harmful to the living soil. Biofertilizers are eco-friendly organic agro-input and more cost effective than chemical fertilizers.
The use of biofertilizers is quite important while practising the concepts of integrated plant nutrient management and organic farming. Some of the commonly used biofertilizers in Kerala are as follows.
1.Rhizobium (Bradyrhizobium and Azorhizobium): It induces better root nodulation and stem nodulation (Azorhizobium) in inoculated plants and thereby brings down the requirement of nitrogen fertilizer for the cultivation of pulses, oil seeds and legume green manures. Commercially it is available as carrier based inoculums. Method of application is seed treatment.
2. Azotobacter: Suitable only for upland crops like vegetables, tapioca, plantation and orchard crops. It is available as carrier-based inoculum. It fixes nitrogen about 15-20 kg/ha under ideal upland conditions and thereby reduces the requirement of nitrogen fertilizers by 10-20 per cent. Methods of application are seed treatment, seedling dip and direct soil application.
3. Azospirillum: It is suitable for both upland and wetland conditions and is available as carrier-based inoculum. It fixes nitrogen about 20-25 kg per ha under ideal conditions thereby effecting a reduction of 25 per cent in the quantity of nitrogen fertilizers required. Treatment with Azospirillum also induces better root formation in inoculated plants; hence this biofertilizer is also recommended for root induction in polybag-raised seedlings of plantation and orchard crops and also for vegetable crops. The isolates of Azospirillum brasilense strains AZR 15 and AZR 37 from Kuttanad soils are highly effective for rice, vegetables and nursery plants. The strains AZ1 and AZ2 are effective in vegetable and nursery plants. Methods of application are seed treatment and seedling root dip (for transplanted crops).
4. Blue green algae (BGA): Mainly recommended for wetland rice cultivation. However, the use of this biofertilizer is not feasible in acidic soils with pH below 6.0. It is available as carrier-based inoculum and it fixes N about 25-30 kg/ha under ideal conditions. The method of application is the direct spreading in the rice fields one week after transplanting the seedlings.
5. Azolla: It is suitable for wetland rice cultivation. The required quantity of azolla will have to be raised in the farmers' field itself. Fixes nitrogen about 25 to 30 kg / ha. The method of application is applying it before transplanting the rice seedlings at the time of ploughing.
6. Phosphate solubilising bacteria and fungi: Recommended mainly for upland crops raised in neutral and slightly alkaline soils. Available as carrier-based inoculum. Enables the efficient utilization of cheaper sources of phosphatic fertilizers such as rock phosphate by crop plants in neutral and alkaline soils. The method of application are the seed treatment and direct application.
7. Vesicular / arbuscular mycorrhiza (VAM/ AM): Vesicular arbuscular mycorrhiza is mostly recommended for upland especially for raising container and tissue culture plantlets and transplanted crops. It mainly improves the uptake of available phosphorus by inoculated plants. There is also an enhanced absorption of water and other nutrients such as nitrogen and pottasium and certain micronutrients. Mycorrhiza inoculation can improve the survival and establishment of tissue culture plantlets under field conditions. Also induces better resistance against certain soil borne plant pathogens. It is commercially available as granular inoculum consisting of infected roots and soil with mycorrhizal spores. It is given as soil application. VAM fungus Glomus microcarpum var. microcarpum is suitable for tropical tuber crops. Method of application is the rooted infected cutting technique.
Factors Influencing the Efficient use of Biofertilizers in Kerala
1. Use adequate quantity of organic manure (as per the recommendation for each crop) along with biofertilizer application. This is essential to ensure better survival, growth and activity of the introduced microbial inoculum in acidic soils.
2. Liming is essential if the soil pH is below 6.0. In moderately acidic soils, the application of lime @ 250 kg/ha is recommended along with biofertilizer treatment.
3. Irrigation is essential during summer months after biofertilizer application to ensure the survival of the introduced microbial inoculum in the soil.
4. Since nitrogen biofertilizers can supplement only a part of the nitrogen requirement of the inoculated plant, low dose of nitrogen and full doses of phosphorus and potassium as per the recommendation may be applied. This is essential to ensure better plant growth and yield. Similarly, in the case of phosphorus biofertilizers, the full doses of nitrogen and potassium should be applied. However, there should be a gap of at least one week between biofertilizer and chemical fertilizer applications.
5. Use only biofertilizers, which are manufactured as per the quality parameters prescribed by the Bureau of Indian Standards. In the case of bacterial biofertilizers, the prescribed standard is that in the final product, the population of the desired bacterium should not be less than ten million per gram of the carrier material and there should not be any contamination with other microorganisms when examined at 1: 100000 dilution. Further, it should have a shelf life of at least six months.
6. The commercially available biofertilizer should always be used before the expiry date marked on the culture packet.
7. Topdressing with super phosphate 25 kg/ha 10 days after inoculation of BGA will enhance its growth under field conditions.
8. Since the occurrence of green algae in rice field can affect the normal growth and copper sulphate @ 4 kg/ha.
9. In moderately acidic soils of pH around 6.5, root nodulation by Rhizobium and Bradyrhizobium can be improved by pelleting with finely powdered calcium carbonate.
10. Application of P2O5 @ 1 kg/ha is recommended once in 4 days in P2O5 deficient soils to ensure good growth of azolla. The development of a reddish purple colour in azolla is a typical symptom of P2O5 deficiency.
11. Since a floating population of azolla can release its bound nutrients only during decay in the soil, it is essential to incorporate azolla in the soil prior to the transplanting of rice seedlings.