Soil salinity is a major environmental hazard which adversely affects plant growth, crop production, soil and water quality and agricultural productivity.Soil salinity is determined by measuring electrical conductivity of soil water suspension. Though saturation paste ECe closely relates with plant growth and development but its measurement is laborious and time-consuming specifically in clayey soils when large number of samples are analyzed. Measurement of EC1:2 (1:2 Soil: water suspension) is very quick and economical. Therefore, a need is felt to develop a relationship between ECe and EC1:2so that the values of EC1:2 could easily be related to ECe. For this, anexperiment was conducted on four soil series representing swell-shrink soils. Soils were artificially salinized with solutions (salt) of 0.2, 0.5, 1 and 2% of chloride salts (NaCl, CaCl2, MgCl2 and their mixture) and replicated three times. The results indicate that a significant relationship (r=0.96) exists between ECe and soil EC1:2and soil ECe can be reliably predicted from EC1:2 in swell-shrink soils.

Soil microbes play an important role in major processes of soil system. Rapid, reliable and cost effective assessment of soil microbiological properties is highly essential for monitoring soil health. Traditional chemical-based soil analysis is laborious, hazardous and time consuming. Visible near-infrared (VIS-NIR) reflectance spectroscopy can be a viable alternative to ensure rapid and environmentally safe soil test results. With this objective, two key soil microbiological parameters microbial biomass carbon (MBC) and dehydrogenase activity (DHA) were examined for their amenability to diffuse reflectance spectroscopy assessment. Geo referenced surface soil (0-15cm) samples (n=170) were collected from different fields for spectral analysis. Partial least square regression (PLSR) technique was employed for developing spectral models. The different model evaluation indices like coefficient of determination (R 2 ), root mean square error of prediction (RMSE) and ratio of performance deviation (RPD) were used to evaluate the predictive performance of model. The RPD values for MBC and DHA were 1.15 and 1.13. Poor predictive performance of our model as opposed to substantial evidence in literature can be ascribed to range of factors like limited variability in spectra, relatively smaller sample size, use of entire spectra instead of selective regions and use of samples collected under natural farm environment as opposed to those generated under controlled conditions. K e y w o r d sDehydrogenase, Land use, Microbial biomass carbon, Reflectance spectroscopy, VIS-NIR models.

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In the present study four representative pedons (viz. Wadhona, Kirnapur, Panjra and Karla)were selected from established shrink-swell soil series in Nagpur district of Maharashtra. The morphological, physical and chemical characteristics of soils were studied and described as per the standard procedure.All the four soil series are, in general, deep to very deep, moderately to poorly drained, rich in shrink-swell clay with the soil colour hue of 10YR and the value varying between 3 and 5 and chroma 1 and 2. The surface soil texture was clayey in all the soil series except Wathena series which was silty clay loam. All the soils are non-saline (EC <0.31 dSm -1 ), surface soil pH (1: 2:: soil: water) varies between 7.8 to 8.7 and organic carbon between 0.56 and 1.12 per cent. Free calcium carbonate found in Panjra and Karla soils varied from 1.29 to 26.72. Soil exchange complex was dominated by Ca 2+ followed by Mg 2+ , Na + and K + with high CEC ranging from 34.7 to 62.6.Taxonomically, the soils of Wadhona series are classified as Typic Haplustepts, Kirnapur and Karla soils as Typic Haplusterts whereas Panjra soils qualify for Calcic Hapluterts.