MATERIALS AND METHODS
The average population density of the district is 2.09 persons per ha (rural) and 2.69 persons per ha (rural + urban). The population density ranges from 1.44 (Bagepalli), 1.69 (Gudibanda), 1.70 (Srinivasapur) to the maximum of 2.55 (Kolar). While, the population density in taluks lies within this range-Bangarpet (2.52), Malur (2.38), Gauribidanur (2.36), Sidlaghatta (2.16), Chintamani (2.10), Mulbagal (2.04), Chikballapur (1.92).
The total forest area of Kolar district is 1039.41 km2 i.e., 12.64 % of the total geographical area. It ranges from 1.71% (Bangarpet), 2.3% (Malur), 2.78% (Kolar) to 15% (Srinivasapur) and 20% (Chikballapur). Taluks are grouped into three (<10%, 10-20% and>20% cover) based on percentage of forest cover. Chikballapur and Bagepalli have forest cover > 20%, Gudibanda and Srinivasapur are in the range of 10-20% while remaining taluks have forest cover < 10%.
Fig. 1: Study area
Livestock is an important component of an agro ecosystem. For instance, livestock provide the critical energy input to the croplands required for ploughing, threshing and other farm operations. Animal dung provides essential nutrients required for soil fertility and crop yields in the form of organic manure. Livestock data was compiled from State Veterinary Department, Government of Karnataka and population density of cattle, buffalo, goat and sheep are found village wise. Data such as livestock (Cattle and Buffalo) population, animal residue and energy demand for domestic purpose data were considered for evaluating biogas potential in a village. Livestock density is evaluated village wise as follows.
Livestock density = Livestock population/Area of the region
Based on this parameter, thematic maps were generated for each taluk, which gives an idea about the livestock in different villages and also helps in comparative analyses.
Biogas is a product of anaerobic fermentation of organic matters and consists of around 60-70% Methane, 30-40% Carbon dioxide. The input material for the biogas materials for biogas digesters are the wastes that are found locally such as animal dung, agricultural residues and leaf litters from forests. The residues are introduced into a closed digester, where without the presence of free oxygen, the responsible microorganisms work successively to convert complex organic matter into CH4, CO2, H2, H2S (Ramachandra, 2003). Quantity of dung yield per cattle varies from place to place. Survey carried out in 1500 households spread across all taulks in the district during January 2005-July 2006 shows that dung available per animal incase of cattle is about 3-7.5 kg/adult animal, buffaloes 12-15 kg, stall fed buffalo about 15-18 kg and hybrid variety is about 15-18 kg. By considering the lower figures (such as 3 kg/cattle/day and 12 kg/buffalo/day), total dung available per day per village is evaluated. With the assumption of 0.036 m3 of biogas yield per kg of cattle/buffaloes dung, the total quantity of gas available (if all is used for biogas) is estimated. It gives the amount of biogas available per village (in low case) (Ramachandra et al., 2005).
Similarly on considering the high figures i.e., (7.5 kg per cattle per day and 15 kg per buffalo per day), total biogas is estimated per day per village and with assumption of 0.042 m3 of biogas yield per kg of cattle/buffaloes dung. It is estimated that per capita requirement of gas for domestic purposes is about 0.34-0.43 m3 per day. Biogas demand is computed by multiplying the adult equivalent of a village population and per capita biogas requirement. Demand of 0.34-0.43 m3 per day was considered for computing low andhigh values ofbiogas demand in a village (Ramachandra et al., 2004). Ratio ofbiogas availability to the demand provides us an idea of the resource status in a region or it gives an idea of the proportion of population's domestic energy requirement could be met by biogas option. Four scenarios were computed depending on resource availability (low and high) and demand (low and high).
Districts map with taluk boundaries and taluk map with village boundaries was digitized to generate base layers using GIS package Maplnfo Professional 6.0 considering Survey of India toposheets (1:50000 scale) and the cadastral map (1:6000 scale) of Kolar. Mapinfo can extract data from an RDBMS (Relational Database Management System). Many thematic maps can be created on the distribution of biogas or bioenergy for a specific year or its predicted values for the future In addition, villagewise livestock density, biogas availability and its demand, biogas status in a village can be illustrated.
The attribute data added to the base layer includes livestock density, area of the village, dung yield and biogas potential. Based on these computations taluk wise biogas availability maps were generated using GIS. The talukwise potential is evaluated using maps of administrative boundaries (taluk boundaries) and statistical data. The theoretical potential is presented as a thematic map of the total amount ofbiogas available in each region considering various scenarios. The information contained in such a map helps to identify regions' biogas status that would help in dissemination and implementation of energy programmes.