“MID-INFRARED SPECTROSCOPY AS A TOOL FOR ASSESSMENT OF SOIL QUALITY IN CALCAREOUS SOILS
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Date
2021
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Dr.RPCAU, Pusa
Abstract
A study entitled “MID-INFRARED SPECTROSCOPY AS A TOOL FOR ASSESSMENT OF SOIL QUALITY IN CALCAREOUS SOILS” was carried out at Department of Soil Science, Dr, Rajendra Prasad Central Agricultural University, Pusa with the objective to evaluate the variability in soil quality parameters, soil quality index and feasibility of mid-infrared (MIR) spectroscopy for prediction of soil quality indicators under rice-wheat system in 275 soil samples collected from West Champaran, East Champaran, Muzaffarpur and Samastipur districts of Bihar which are calcareous in nature. Soil samples were analyzed in the laboratory for different physical, chemical and biological properties by Cornell Soil Health Laboratory Comprehensive Assessment of Soil Health (CASH) standard operating procedures. Soil textural class of the samples varied from clay to sand with most frequent textural class of silt loam. A wide variation was observed for soil quality parameters which included Wet Aggregate Stability (WAS) (0.24-88.93 %) with mean 24.78 %; pH (5.76-9.67) with mean 8.39 (±0.53); electrical conductivity (EC) (0.11-2.77 dSm-1) with mean 0.41 dSm-1 (±0.27); free calcium carbonate (CaCO3) (0.04-54.1%) with mean 18.78 % (±12.64) and soil organic carbon (SOC) (0.14-1.26 %) with mean 0.63 % (±0.20). Among the soil major nutrients, the variation of available N was between
120.35-315.30 kg ha-1 with mean 204.5 kg ha-1 (±34.24); available P2O5 was between 0.90- 422.62 kg ha-1 with mean 103.73 kg ha-1 (±91.77); available K2O was between 31.05-1471.01 kg ha-1 with mean 204.98 kg ha-1 (±146.35) and available S was between 0.37-538.44 ppm with mean 39.3 ppm (±61.41). The variation in available soil micronutrients were as follows: Zn between 0.04-3.30 ppm with mean 0.77 ppm (±0.66); Cu between 0.00-5.18 ppm with mean 1.45 ppm (±0.75); Fe between 2.42-31.65 ppm with mean 10.5 ppm (±5.13); Mn between 0.00-13.82 ppm with mean 4.14 ppm (±2.74); and B between 0.00-7.6 ppm with mean 0.52 ppm (±0.67). Among the soil biological properties, active C, autoclaved citrate extractable protein (ACE), and respiration varied between 6.96-731.38 mg kg-1, 0.32-4.26 g kg-1 and 0.05-4.25 mg CO2 g-1 respectively and their mean values were 256.46 mg kg-1 (±193.4), 1.72 g kg-1 (±0.80) and 0.54 mg CO2 g-1 (±0.34) respectively. The first seven principal components (PCs) factors obtained with principal component analysis (PCA) of twenty soil quality parameters with eigenvalues >1 explained that CaCO3, pH, sand, protein, Fe, S, EC, silt, SOC, N, clay, B and K2O contributed 67.86 % of the soil variability in calcareous soil of Bihar. The soil quality index (SQI) values of all the 275 samples of calcareous soils of Bihar lied between 0.29-0.64 with a mean 0.47, which belongs to a low class of SQ. In the MIR spectroscopy study, principal component regression (PCR) and partial least square regression (PLSR) algorithm in OPUS software were used for understanding the quality of prediction level of the soil studies. Best models for residual prediction deviation (RPD) values with ―MIR-PLSR‖ were obtained for SOC, available N, free CaCO3, sand, silt and clay. Prediction for pH, EC, micronutrients (except B), WAS, active C, protein and respiration were observed as fair models. This indicated that MIR spectroscopy has great potential for simultaneous estimation of a number of soil properties in larger soil sample size and is useful for the prediction of soil quality parameters.