BIOFERTILIZERS
• Microrganism – Function
Rhizobium spp. – Nodulation and nitrogen fixation
Arbuscular Mycorrhizae – Nutrient mobilization
Phanerochaete chrysosporium – Composting
Azolla – Improve nitrogen availability in rice
Bacillus megaterium – Silicate/Phosphate solubilization
• Biofertilizers can be applied as seed coating, soil application or seedling dip.
• Dry formulations of microbial inoculants can be in the form of dusts, wettable powders, granules, pellets, capsules and briquettes.
• Commonly used carriers for biofertilizers are peat, lignite, soil, charcoal, vermiculite, talc, vermicompost, sawdust and pressmud.
• Biofertilizer – specific crop
Azospirillum – Cereals, particularly grasses
Blue green algae – Rice
Frankia – Casuarina
Azotobacter – cotton
• Frankia fixes nitrogen.
• Rhizobium establishes efficient symbiotic associations with pulses, leguminous oil-seeds and fodder crops.
• For seed treatment, Rhizobium inoculum @ 1.5kg/ha is mixed in the jaggery solution and sprinkled over the seeds.
RHIZOBIUM SPECIES SUITABLE FOR DIFFERENT CROPS
| Rhizobium sp. | Crops |
| R.leguminosarum | Peas (Pisum), lathyrus, Vicia, Lentil (Lens) |
| R. trifoli | Berseem (Trifolium) |
| R. phaseoli | Kidney bean (Phaseolus) |
| R. lupini | Lupinus |
| R.japonicum | Soybean (Glycine) |
| R. meliloti | Melilotus, Lucerne (Medicago), Fenugreek (Trigonella) |
| Cowpea miscellany | Cowpea, cluster bean, greengram, blackgram, redgram, groundnut, moth bean, dhaincha, sunhemp, Glyricidia, Acacia, Prosophis, Dalbergia, Albizzia, Indigofera, Tephrosia, Atylosia, Stylo |
| Separate group | Bengalgram (gram) |
• Free living organisms that can fix atmospheric nitrogen are blue green algae (BGA), Azolla, Azotobacter and Rhizospirillum.
• BGA and Azolla can survive only in lowland conditions.
• Important species of BGA that fix atmospheric nitrogen are Anabaena and Nostoc.
• Amount of nitrogen fixed by BGA ranges from 15-45 kg N/ha.
• BGA can grow at a temperature of 25 to 45 oC.
• Bright sunshine increases the growth rate of BGA while rains and cloudiness slows growth rate.
• BGA grows well in a pH range of 7 to 8 and in soils with high organic matter.
• BGA inoculum is applied after transplantation of rice crop in the main field.
• Amount of BGA inoculums required is 10 kg/ha.
• Azolla is a free-floating water fern which forms symbiotic association with blue-green algae species Anabaena azollae present in the lobes of Azolla leaves and provides nitrogen to rice crop.
• Azolla pinnata is the most common species occurring in India.
• A thick mat of Azolla supplies 30-40 kg N/ha.
• Unlike blue-green algae, azolla thrives well at low temperature.
• Normal growth of Azolla occurs in the temperature range of 20 to 30 oC.
• Azolla grows better under monsoon season with frequent rains and cloudiness.
• For Azolla suitable soil pH is 5.5-7.0.
• Amount of Azolla inoculum required is 0.1 to 0.5 kg/m2.
• As green manure crop, Azolla is allowed to grow on the flooded fields for 2 to 3 weeks before transplanting, later water is drained and Azolla is incorporated by ploughing in.
• Advantages of Azotobacter to crops are Biological nitrogen fixation, release of growth promoting substances, suppression of plant diseases.
• Azotobacter chroococcum is capable of fixing 20 to 30 kg N/ha.
• Amount of Azotobacter inoculums required is 3-5 kg/ha.
• Azotobacter can be used for rice, cotton and sugarcane.
• Acetobacter is commercially utilized for Sugarcane.
• Azospirillum inoculants are recommended in several crops such as jowar, bajra, ragi and other millets.
• Cell number or colony forming units at the time of manufacture should not be less than 108 and 107 per gram of carrier material, respectively for Rhizobium and Azotobacter.
• Pseudomonas striata, Aspergillus awamorii and Bacillus polymyxa are capable of solubilising phosphates.
• Liquid inoculants and biofilmed inoculants are new generation biofertilizers.
• Shelf life of liquid biofertilizers is 12-24 months.
• Gross quantity of crop residues annually available in India is 686 million tonnes.
• Crop – residue to economic yield ratio
Rice – 1.4
Wheat – 1.3
Maize – 2.0
Barley – 1.5
• Out of the total residue produced in India, cereal crops contribute the highest amount followed by sugarcane.
• The silica content in rice straw is 12-16% and wheat straw is 35%.
• Wheat straw contains approximately 0.53% N.
• C:N ratio of wheat straw is more than rice straw.
• The rice straw contains 50-100% higher concentration of K than in wheat straw.
• Machines used for zero-till planting of crops under surface residue conditions is turbo happy seeder, rotary disc drill and double disc drill.
• Hydraulic conductivity and infiltration rate are higher in no-till with residue retention compared to conventional till with residue incorporation.
• Gas – Qty released by burning 1 tonne of rice residue
CO2 – 1515 kg
CO – 92 kg
NOx – 3.83 kg
CH4- 2.7 kg
Non-methane volatile organic compounds – 15.7 kg
SO2 – 0.4 kg
• Nutrient – Content in 1 tonne rice straw
N – 5-8 kg
P – 0.7 -1.2 kg
K – 15-25 kg
S– 0.5 -1 kg
Ca – 3-4 kg
• Cellulose content in crop residues on dryweight basis is 15-60%.
Hemicellulose-10-30%
Lignin-5-30%
Protein– 2-15%
• The potential of no-till can be fully realized only when it is practiced continuously and the soil surface is covered at least 30% by crop residues or other organic materials.
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