Dinesh Kumar Benbi

Prevention and control of water pollution for maintaining and restoring the wholesomeness of rivers are unavoidable. The current water quality approach of designated best use has some limitations such as it is non-integrative and inflexible with regard to the consideration of variables and does not provide a separate rating scale for a given designated use. We thus used water quality index approach proposed by the Canadian Council of Ministers of the Environment (CCME WQI) to evaluate and develop a separate rating system for drinking and irrigation purposes of rivers Beas, Satluj and their confluence water of the Indian Punjab using information collected over 4 years (2016 to 2019). River Beas exhibited better water quality compared to river Satluj for irrigation as well as for drinking. The overall drinking water quality index (DWQI) for Beas was marginal (45.5), whereas it was poor for Satluj (37.7) and confluence waters (40.1). The spatial variation in DWQI was greater for Satluj compared to Beas and confluence waters reflecting the effect of dumping of untreated industrial and domestic waste waters. Variables such as Total coliform (T. coli), dissolved oxygen (DO), turbidity and biological oxygen demand (BOD) contributed to the deterioration of DWQI. The irrigation water quality index (IWQI) was good for Beas (86), marginal for Satluj (60.1) and fair for confluence waters (71.2). Faecal coliform (F. coli), Kelly ratio (KR) and %Na contributed to the deterioration of IWQI. Calcium-magnesium-bicarbonate (Ca-Mg-HCO₃) was the dominant water type in Beas and confluence waters, whereas for Satluj, in addition to Ca-Mg-HCO₃, sodium-potassium-chloride-sulphate and mixed water types were also prevalent. The river waters witnessed salinity hazard but did not pose sodicity hazard except at a few locations of Satluj. The study indicates the need to take location specific measures for improving river water quality for drinking as well as irrigation purposes. The current status of water quality calls for an urgent need to formulate stringent policy regulations to maintain the surface water quality.

Open field burning of rice straw besides causing environmental pollution and human health problems results in loss of organic carbon and essential nutrients. Urgent solution is required for management of rice straw in an eco-friendly and sustainable manner. The aim of the present study was to examine the efficiency of direct return of rice straw into the soil versus biochar generated from rice straw, and compare it with wood derived biochar in influencing soil biological processes and potential to accumulate soil organic C (SOC). We studied the effect of pyrogenic conversion of rice straw and wood chips to biochar on changes in chemical composition of feedstock by Fourier Transform Infrared (FTIR) spectroscopy and C and N mineralization kinetics, microbial metabolism, carbon use efficiency (CUE) and soil enzyme activities in a series of laboratory incubation experiments conducted at 25 °C temperature and field capacity moisture. Pyrogenic conversion of feedstock to biochar resulted in increase in C (39.6% to 69.2%) and N (0.4% to 1.65%) contents and lowering of C/N (99 to 28.4) and H/C (1.94 to 0.60) ratios. Charring resulted in decrease in aliphatic and increase in aromatic components. Decomposition of organic substrates was governed by aromaticity and C/N ratio; in 127 days, only 12% of rice straw biochar embodied C was mineralized as against 76% from rice straw. The addition of biochars resulted in soil N priming (120 ± 24 mg N kg⁻¹) whereas straw application resulted in net N immobilization (−13 mg N kg⁻¹). Compared to unpyrogenic straw, the rice straw biochar led to greater microbial growth, lower metabolic quotient, higher CUE (3.3 times) and decreased microbial respiration, with potential to promote SOC accumulation. It was concluded that addition of rice residue generated biochar into soil is more beneficial for soil biological processes and SOC stabilization to stymie climate change than direct return of plant residue into the soil. The results are significant for devising eco-friendly rice residue management practices in the Indo-Gangetic plains.

Soil respiration (Rs) measurements in relation to agricultural management and environmental variables are necessary to improve our understanding of net ecosystem carbon balance (NECB) and to predict soil’s feedback to climate change. The objectives of this study were to analyse the seasonal dynamics of Rs in maize-wheat and cotton-wheat crop rotations and to quantify the effects of temperature, moisture and management on Rs and NECB. Soil respiration was measured in situ by open chambers over two years. In-season Rs varied with crop growth and peak rates coincided with maximum growth stage of a crop. Soil respiration rate was higher in maize than in cotton. Mean Rs in winter wheat was about 1/3^rd of that in preceding maize or cotton. Root respiration comprised 13-29% of Rs in different crops. The NECB suggested that soil could be losing organic C at 381 to 643 g C m⁻² y⁻¹. Application of organic amendments along with inorganic fertilizers improved NECB underpinning their role in converting a cropping sequence from potential source to sink of carbon. Temperature sensitivity of Rs was strongly modulated by soil moisture suggesting that increased Rs due to warming coupled with high moisture could provide a positive feedback to climate change.