Biofertilizers for Greenhouse Grown Crops
Author: Pravin L. Deshmukh

The farmers all over the world are turning more and more towards biological agriculture as they increasingly encounter the hazardous effects of chemical fertilizers and their prohibitive costs. Biological farming aims at preserving the natural and ecological balance according to the environmental standards. Biofertilizers are the essential soil inputs used in farming that help to develop and sustain soil texture and soil fertility, they are easy to use and can be used for all types of fruits, vegetables, lawns, ornamental plants, home garden and cash crops. For green house grown crops especially for chillies, bell pepper, lady's finger, tomato, beans and flowers of various types.

1. Biofertilizers

Biofertilizers are the microbial preparations containing live cells of bacteria/ cyanobacteria/fungi which efficiently fix atmospheric nitrogen, solubilize insoluble phos­phate in soil or decompose cellulosic organic wastes. The efficient strain of the requisite microbial agent is grown on specific nutrient medium on large scale aseptically, mixed in a suitable carrier and the preparation so formulated is sold as biofertilizer. Biofertilizers are also called as bioinoculants, microbial cultures, bacterial inoculants or bacterial fertilizers.

2. Types of Biofertilizers

Biofertilizers are grouped in three categories depending on kind of beneficial activity carried out by the microbial agent used in their production. These include:

  1. N fixing biofertilizers,
  2. Phosphate solubilizing biofertilizers and
  3. Decomposing cultures.
Besides these, the microbes, which oxidize sulphur, are also known but their commercial preparations as biofertilizers have not been yet developed and popularized. Carrier based inoculum of above three types of microbial preparations have been commercialized on lagre scale. Recently very few private firms have come forward with the manufacture of liquid biofertilizers which have limited use in their applications.

a) Nitrogen Fixing Biofertilizers:

These include the preparations of bacteria/cyanobacteria which convert atmospheric gaseous nitrogen (N2) to ammonia and make it available to the plants. The organisms, which fix atmospheric nitrogen, are called as diazotrophs. Biazotrophs belong to prokaryotic group and none of the members from eukaryotic group is able to fix atmospheric nitrogen. The nitrogen-fixing organisms include species of Rhizobium, Azotobacter, Azospirllum and blue green algae (cyanobacteria). These are used in commercial production of biofertilizers. Recently, Acetobacter diazotrophicalis is reported to be potential N fixer in vegetable crops.

b) Phosphate Solubilizing Biofertilizers:

These are prepared from the microorganisms, which solubilize fixed phosphorus in soil and make it availables to the plants. The most of P in the form of phosphatic fertilizers added to soil becomes unavailable to the plants due to phosphate fixing capacity of soil. To benefit fully from added P fertilizers in soil, new technology has been recommended in the form of use of phosphate solubilizing biofertilizers. The bacterial isolates reported as phosphate solubilzers includePseudomonas striata, Pseudomonas rthonis, Bacillus polymyxa and Bacillus megatherium var. Phosphaticum. The fungal isolates reported to be efficient P solubilizers are Aspergillus awamori and Penicilium digitatum. Phosphatic biofertilizers have been reported more effective when used in combination with N fixing biofertilizers. Lignite based preparations of phosphatic biofertilizers are recommended for use as seed treatment, while sorghum grain based phosphatic biofertilizers are used for addi­tion in compost pit or added along with compost for horticultural crops.

c) Compost Cultures:

Compost cultures (biofertilizers) are prepared from cellulolytic microbes, which decompose organic wastes rapidly and yield good quality compost. The fungi belonging to the genera viz., Trichoderma, Penicillium, Chaetomium, Aspergillums and Aureobasidium and the bacteria belonging to the genera viz.,Bacillus, Pseudomonas, Ceilvibrio, Celiulomonas and Cytophaga are known as efficient organic matter decomposers. These are used for decomposing organic wastes in compost pit. For one metric ton of organic residues 500 g grain based decomposing culture is sufficient. Use of compost cultures enhances the rate of organic matter decomposition and result in good quality compost.

3) Production Technology:

N- fixing biofertilizers are prepared from the bacteria/ cyanobacteria which converts atmospheric gaseous nitrogen (N2) to ammonal and make it available to plant. The nitrogen fixing organisms include species of rhizobium, Azotobacter, Azospirillurn and blue green algae (cyanobactena). For harvesting live cells in large numbers the efficient cultures are inoculated in N free liquid media and using either shake cultures or industrial fermentors within 3 to 4 days the maximum cell population is obtained. The cultures are mixed in sterile carriers and on having curing for two days the packets are prepared. Another technique involves use of compressors and filters the sterile air is allowed to pass in flasks containing broth of inoculated biofertilizers agent.

Phosphate solubilizing biofertilizers are prepared from Phosphate solubilizing bacteria (PSB) or fungi(PSF). Carrier based preparations are manufactured as that of N fixing biofertilizers. Another technology involves production of sorghum or any other cereal grain based phosphatic fertilizers. Cereal grains are soaked in water for 24 hours and after sterilization inoculated with efficient cultures of phosphate solubilizing fungi. On full growth on grains the biofertilizers packets are prepared.

Compost cultures (biofertilizers) are prepared from cellulolytic microbes, which decompose organic wastes rapidly and yield good quality compost. The fungi belonging to the genera viz.,Trichoderma, Penicilium , Chaetomium, Aspergillus andAureobasidium and the bacteria belonging to the genera viz.,Bacillus, Pseudomonas, Cellvibrio, Cellulomonas andCytophaga are known as efficient organic matter decomposers. Cellulolytic microbes are grown on any cereal grains and biofertilizer packets are prepared. These are used for decomposing organic wastes in compost pit.

4. Methods of Application

Lignite based biofertilizers are recommended for use as seed treatment in seed sown crops and in raising seedling and in addition, by seedling root dip method in transplanted crops. The grain based bioinoculant are used for addition in compost pit or added along with compost for horticulture crops. For seed sown green house crops carrier based biofertilizers are treated to the seed by slurry method. Generally for treating 10 kg seeds 200 g of biofertilizer is used. For this two packets of biofertilizers (400g) are sufficient to treat the seedlingfor transplanting one acre area. Considering the cultivated area of greenhouse crops, the the required quantity or biofertililzer is added in sufficient quantity of water @ 1 packet in 500ml and roots of seedlings are dipped in slurry for 3-4 minutes before planting of seedlings.

5. Quality of Biofertilizers

The reasons of poor quality biofertilizers are use of ineffective microbial strain, insufficient number of viable cells, presence of contaminants, production by unskilled staff, poor shelf life and inadequate facilities. The quality control norms are specified only for rhizobium and azotobacter biofertilizers and that too, they are not compulsory for all the producers in India. This is the main constraints, which possess the problem of production of large quantities of poor quality biofertilizers and to authorize government institutions/ agriculture universities to check the quality of biofertilizers produced and to discourage the manufactures from producing substandard biofertilizers.

6. Biofertilizers utility for Green House grown crops:

Biofertilizers agents secretes auxins and hormones thereby increasing germination. Once the biofertilizers are applied, they cannot be leached out, evaporate of lost but increase in number and supply the nutrients throughout the life span of green house crops. Biofertilizers agents also exhibits fungicidal action. Application of biofertilizers does not affect the texture of soil/planting medium for green house crops, but improved the structure and texture. Cost per unit nitrogen is less than chemically fixed nitrogen. Biofertilizers Increase nitrogen fixation, phosphate solubilization, sulphur oxidation and supplies other macro and micro plant nutrients essential for balanced nutrient supply and growth. As well they increase vegetative growth, increasing total dry matter production and increase yield producing quality product. Biofertilizers are useful in maintaining and improving fertility status of planting medium for green house crops.

About Author / Additional Info:
Ph.D. Scholar, Department of Horticulture, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola, Maharashtra-444104.