A field study was conducted during kharif 2012 and 2013 to know the spatial variability in available nutrient content in cultivator’s field for site specific nutrient management with mechanisation in groundnut at the Central Dry Zone of Karnataka under the jurisdiction of University of Agricultural Sciences, GKVK, Bangalore, India. The farmer’s fields have been delineated with each grid size of 50 x 50 m using geospatial technology and also DGPS locations have been used for each grid to map the field variability. After grid making soil samples from 0-15cm were collected and analysed for different major and micro nutrients in all the selected 139 grids. Results indicated that significant variability of essential plant nutrients exists in different operating systems in which each farmers family was assigned to operate several small field plots with the field size ranging from 0.8 ha to 3.2 ha. The large spatial variability of soil nutrients was mainly due to the fertilizer history of individual farmers, diversity of crop types and varieties used. There was a strong correlation between crop yields and available soil nutrient levels at the corresponding sites in the field. Based on the understanding of the nature of spatial variability of soil nutrient availability in Central Dry Zone of Karnataka and with the purpose of increasing profitability and sustainability of crop production a site specific nutrient management strategy was proposed. Related techniques adopted and discussed including soil testing and fertilizer recommendation in farmers plots, state recommendations in comparison with precision farming plots. Assessment, quantification of spatial variability of the field for PH, EC, major and minor nutrients, pest and yield are done through GIS mapping in order to supplement the right quantity of nutrients and pesticides on right time on right quantity and right method. The available nitrogen status of soil revealed that 8, 80, 12 per cent was low, medium and high respectively, while the available phosphorus level remained lower for 96 per cent of samples and 84 per cent of the samples found to be medium in available potassium .The available sulphur and zinc status remained lower. It was also assessed for its variability spread in the field and insecticides were given as per variability by which we saved in the cost on pesticides. The analysis of two years data showed that precision nutrient management with mechanized cultivation recorded 52.1 and 22.0 per cent higher pod yield of groundnut over farmers method and state recommendations respectively.
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