INFLUENCE OF ORGANIC MANURES (BIOFERTILIZERS) ON SOIL MICROBIAL POPULATION IN THE RHIZOSPHERE OF MULBERRY (MORUS INDICA L.)

The effect of different kinds of organic manures on soil microbial population and mulberry production was assessed. A field experiment was carried out at Periyar EVR College, Tamil Nadu, India in basic soil to study the influence of organic manures on soil bacterial population and mulberry production. The 4 groups of mulberry plants of MR2 variety were biofertilized with FYM, Azospirillum, Phosphobacteria and Vermicompost respectively. The biofertilizers lodged bacteria on the rhizosphere of mulberry plants. When the root microorganism are analyzed Farm yard manure biofertilized mulberry plant root tips had Gluconacobacter diazotrophicus, Bacillus pumilus, Pseudomonas putida, Bacillus coagulans, Bacillus sonorensis, Azotobacter chrococcum; Azospirillum biofertilized mulberry plants root tips had Bacillus coaculans, Azotobactor chrococcum, Azotobactor vinelandii, Bacillus subtilis and Azospirillum brasilense. Phosphobacteria biofertilized mulberry plant root tips had Pseudomonas putida, Bacillus stearothermophilus, Brevibacillus borslelansis and Streptomycies thermonitrificans and vermicompost biofertilized mulberry plant root tips had lodged bacterias like Bacillus megaterium, Bacillus subtilis, Gluconacobacter diazotrophicus, Pseudomonas putida, Azotobacter chrococcum, Azotobacter vinelandi, Bacillus stearothermophilus, Brevibacillus borslelansis and Bacillus sonorensis. Microbiology work reveals luxuriant growth of bacteria in all the biofertizer treated rhizosphere in the order FYM < Azospirillum < Phosphobacteria < Vermicompost. Increased availability of NPK and other micronutrients were noticed in T4 treated plants compared to other treatments.


Introduction
Organic agriculture is a production system which avoids largely excludes the use of synthetically compounded fertilizers, pesticide, fungicides, growth regulators and livestock feed activities (Lampkin, 1990). The organic matter of a particular material may be of the beneficial effects of organic matter on improvement of soil properties and productivity (Dahama, 1999). The organic production system aims at largely to utilize the available biomass of the farm to enrich soil fertility, to supply balanced nutrients to the plants and also to reduce the cost production as well as the environmental pollution (Ramakrishna et al., 2002). Organic amendments not only support sustained crop production, but also improve the soil microbial activity (Dagar and Gautam, 2002). The mulberry leaf yield and quality depends on the soil type, plant variety, availability of plant nutrients and agro-ecological conditions, which reflects on the quality of silk production. Mulberry leaf productivity is highly dependent on plant nutrients like NPK and known to respond well to the addition of organic manures. The chemical fertilizers are becoming costlier day by day due to escalating costs and scarce availability of commodities. The highly intensive mulberry cropping system causes depletion of nutrients in soil and excess usage of inorganic fertilizers and pesticides caused deleterious effect on soil health.
In this context, supply of major nutrients to mulberry through organic manures and biofertilizers is highly imperative. Organic manures are bulky in nature which supplement the crop with small amounts of major nutrients like NPK and other minor nutrients required by the crop and encourages the proliferation of soil microflora (Lakshmi, V et al., 1977). Introduction of crop benefiting microbial inoculants in the soil play a significant role in the mobilization of various nutrients needed by the crop (Kumar and John, 1990) reported that, application of microbial inoculants in conjunction with organic manures has significantly increased the productivity of mulberry leaf.
With this background the present investigation was carried out to know the effect of major nutrients supplied through organic sources on soil microflora and fertility status of mulberry garden under irrigated condition.

Materials and Methods
A field experiment was carried out during 2012 -2013 in an established irrigated MR2 Mulberry garden planted at a spacing of 50cm × 50cm. The experiment was laid out with 4 treatment of 3 replications each. After the establishment period of mulberry plantation, biofertilizers were applied at 20 Kg/ha/yr.  Yadav and Nagendra Kumar (1989) also opined better N fixing ability of Azospirillum contributing to nitrogen economy and soil fertility. Goswami (1997) had also reported that 20 to 400 kg/ha of N can be added to the soil by N fixing bio-inoculants. Similar results were also obtained earlier by Rashmi et al. (2007) and Murali et al. (2006) who have asserted increased availability of NPK when biofertilizer were integrated with different types of organics. According to Alemu and Bayu (2005) four years application of FYM at the rate of 10 and 15 kg/ha had increased total N of the soil, organic carbon, available P, K and Mg when compared to the plants lacking FYM application in the 0 -20 cm soil depth. Similarly Sori et al. (2008) found that the mulberry gardens treated with bioinoculants at 20 kg / ha of Azotobacter + 25 kg/ha of A. awamori + 20 kg/ha of T. harzianum + 75% recommended nitrogen and phosphorus each through chemical fertilizer with full recommended dose of FYM and K had recorded maximum available NPK. The application of bacterial inoculants as biofertilizers has been reported to result in improved plant growth and increased yield (Bashan andHolguin, 1998 andVessay, 2003). Gupta et al., (1995) reported that the inoculation with Azospirillum sp., Azotobacter chrococcum and Pseudomonas fluorescence significantly improved seedling emergence rate. A. chrococcum was most effective in increasing the total dry weight of root and shoot length.

Soil microbes in the rhizosphere of mulberry
Gluconacetobacter diazotrophicus is a variety of diazotrophic bacteria have been isolated from rhizosphere and roots of sugarcane plants. In 1998, Cavalcante and Dobereiner reported an acid-tolerant N-fixing bacterium Acetobacter diazotrophicus, associated with sugarcane which contributed abundant N to sugarcane crop with a capability to excrete almost half of the fixed N in a form that is potentially available in plants, G. diazotrophicus is a gram-negative, acid-tolerant, obligate aerobe and the cells are straight rods with rounded ends (0.7 -0.9 μm by 1 -2 μm). The cells can be seen under 48 microscope as single, pair or chain like structures without endospores. Recent studies on association of G. diazotrophicus with rice seedlings seem to be encouraging, where a substantial increase in growth of rice plants (ponni) was recorded. With the increasing cost of chemical fertilizers and concern about environmental pollution, the role of biological nitrogen fixation (BNF) in supplying plants with needed N, which can make agriculture more productive and sustainable without harming the environment has to be harnessed efficiently. As BNF is not restricted to legumes only, for sustainable agriculture it becomes necessary to increase the amount of biologically fixed N in non-legume crops also. Significant nitrogen input into the global nitrogen cycle, has been reported through the Azolla-Anabaena symbiosis (Plazinski, 1989), nitrogen fixation by free living cyanobacteria, Azotobacter, Azospirillum and Pseudomonas species (Krotzky et al., 1987;Cavalcante et al., 1998).
Studies indicate that rhizosphere, roots, stems and leaves of even healthy plants harbour diverse microbial communities that include N fixing bacteria (Boddey et al., 1991) and part of the N accumulated by non-leguminous plants was proved to have been fixed by the root-zone bacteria (Loganathan et al., 1999). A special term diazotrophic associative symbiosis, was suggested to describe the process of N fixation in the plant root zone (Vose and Ruschel, 1982).
Psuedomonas putida is a rod shaped, flagellated, gram negative bacterium that is found in most soil and water habitats where there is oxygen. The surface of the root, rhizosphere, allows the bacteria to thrive from the root nutrients. In turn, the Pseudomonas putida induces plant growth and protects the plants from pathogens because P. putida assist in promoting plant development, researchers use it in bioengineering research to develop biopesticides and to improve plant health (Espinosa-Urgel et al., 2000).
Azotobacter vinelandii is a diazotroph that can fix nitrogen while grown aerobically. It is a free living N2 fixer which is known to produce many phytochromes and vitamins in the soil.
Azotobacter chrococcum, was discovered and described in 1901 by the Dutch Microbiologist and Botanist, Martinus Beijerinck. They are found in neutral and alkaline soils (Gandora et al., 1998). Azotobacter synthesize some biologically active substances, including some phytohormones such as auxins (Ahmad et al., 2005). They also facilitate the mobility of heavy metals in the soil and thus enhance bioremediation of soil form heavy metals, such as cadmium, mercury and lead (Chen et al., 1995). Similar results were also obtained earlier by Rashmi et al., (2007) and Murali et al., (2006) who have established the increased availability of NPK when biofertilizers were integrated with different types of organics.

Soil nutrient status of different biofertilizer treated mulberry plots
The results of the present investigation revealed that the pH of FYM soil was 7.06 and pH of biofertilized mulberry plots ranged between 6.89-7.59. This may be due to interaction of biofertilizers in the rhizosphere of soil. Significant variations in mineral nutrients were found. They were found to be highest in vermicompost biofertilized soil, higher in phosphobacteria biofertilized soil, high in azospirillum biofertilized soils and low in FYM biofertilized soils. Available nitrogen ranged 87.6 -118.5 kg/ac, available phosphorus 3.56 -6.39 kg/ac and potassium105 -178 kg/ac. Available manganese ranged 2.63 -3.45 ppm, available iron ranged 4.58 -6.25 ppm (Table 2), available zinc ranged 0.96 -1.36 ppm, available copper ranged 0.56 -1.09 ppm ( Table 2). The data revealed that the microbial inoculants in the biofertilizers influenced the available nutrients status in the rihzosphere of soil. Similar results were reported by Sharma et al., (2002).
According to Alemu and Bayu (2005), four years application of FYM at the rates of 10 and 15 t ha-1 increased the soil total N, organic carbon, available P, K and Mg compared to the plot lacking FYM application in the 0 -20 cm soil depth. Similarly, according to Sori et al., (2008) the mulberry gardens treated with bio-inoculants at 20 kg/ha of Azotobacter + 25 kg/ha of A. awamori + 20 kg/ha of T. harzianum + 75 percent recommended nitrogen and phosphorus each through chemical fertilizer with full recommended dose of FYM and K has recorded maximum available NPK. The increased availability of NPK in soil may be attributed to better nitrogen fixing capacity of Azotobacter, solubilisation and mobilization by A. awamori and T. harzianum in the presence of FYM and Inorganic Fertilizer (IF).

Conclusion
From the above findings it is concluded that application of different biofertilizers plays a significant role in enhancing the soil fertility in terms of macro-nutrients, secondary nutrients and microbial population. The microbial population helped in enriching the soil with major nutrients like N and P which are mainly essential for luxuriant growth of plants.