Imprint of clay mineralogy, sesquioxides, and crop residue addition for evaluation of soil organic carbon stability and associated microbial activity in dominant soil orders of Indian subcontinent.

The full behaviour of natural clay minerals in soil organic carbon (SOC) stabilization in the presence of oxides and external C inputs is yet unknown. Thus, an incubation experiment was conducted in a sand-clay mixture with different soil clay fractions (SCFs) obtained from Alfisol, Inceptisol, Mollisol, and Vertisol in the presence of wheat residues to compare their C stabilization capacity. The C mineralization rates were higher in 1:1 type dominated SCFs (Alfisol and Inceptisol) compared to 2:1 interstratified mineral dominated SCFs (Vertisol). Wheat residues as C source altered SCFs' abilities to stabilize SOC at only moderate dosages of application (3-12 g kg-1). C mineralization and microbial biomass carbon (MBC) fell by 40% and 30%, respectively, as the amount of clay increased from 7.5 to 40%. However, removing sesquioxides from the SCFs boosted C mineralization and MBC by 22% and 16-32%, respectively, which matched with higher enzymatic activities in the sand-clay mixture. The increased C stabilization capacity of Vertisol-SCF may be attributed to its greater specific surface area (SSA) (506 m2 g-1) and cation exchange capacity (CEC) [meq/100 g]. Regression analysis revealed that SSA, CEC, and enzymatic activity explained approximately 86% of total variations in C mineralization. This study highlighted the critical role of 2:1 expanding clay minerals and sesquioxides in greater stabilization of external C input compared to its 1:1 counterpart. It also implied that the role of mineralogy or texture and sesquioxides levels in different soils (Vertisol, Mollisol, Inceptisol, Alfisol) should be prioritized while adding crop residues to reduce C footprint and enhance sequestration.

Nitrification and urease inhibitors mitigate global warming potential and ammonia volatilization from urea in rice-wheat system in India: A field to lab experiment.

The efficacy of alternative nitrogenous fertilizers for mitigating greenhouse gas and ammonia emissions from a rice-wheat cropping system in northern India was addressed in a laboratory incubation experiment using soil from a 10-year residue management field experiment (crop residue removal, CRR, vs. incorporation, CRI). Neem coated urea (NCU), standard urea (U), urea ammonium sulfate (UAS), and two alternative fertilizers, urea + urease inhibitor NBPT (UUI) and urea + urease inhibitor NBPT + nitrification inhibitor DMPSA (UUINI) were compared to non-fertilized controls for four weeks in incubation under anaerobic condition. Effects of fertilizers on global warming potential (GWP) and ammonia volatilization were dependent on residue treatment. Relative to standard urea, NCU reduced GWP by 11 % in CRI but not significantly in CRR; conversely, UAS reduced GWP by 12 % in CRR but not significantly in CRI. UUI and UUINI reduced GWP in both residue treatments and were more effective in CRI (21 % and 26 %) than CRR (15 % and 14 %). Relative to standard urea, NCU increased ammonia volatilization by 8 % in CRI but not significantly in CRR. Ammonia volatilization was reduced most strongly by UUI (40 % in CRI and 37 % in CRR); it was reduced 28-29 % by UUINI and 12-15 % by UAS. Overall, the urease inhibitor, alone and in combination with the nitrification inhibitor, was more effective in mitigating greenhouse gas and ammonia emissions than NCU. However, these products need to be tested in field settings to validate findings from the controlled laboratory experiment.

Enhancing cation and anion exchange capacity of rice straw biochar by chemical modification for increased plant nutrient retention.

Biochar, a potential alternative of infield crop residue burning, can prevent nutrient leaching from soil and augment soil fertility. However, pristine biochar contains low cation (CEC) and anion (AEC) exchange capacity. This study developed fourteen engineered biochar by treating a rice straw biochar (RBC-W) first separately with different CEC and AEC enhancing chemicals, and then with their combined treatments to increase CEC and AEC in the novel biochar composites. Following a screening experiment, promising engineered biochar, namely RBC-W treated with O3-HCl-FeCl3 (RBC-O-Cl), H2SO4-HNO3-HCl-FeCl3 (RBC-A-Cl), and NaOH-Fe(NO3)3(RBC-OH-Fe), underwent physicochemical characterization and soil leaching-cum nutrient retention studies. RBC-O-Cl, RBC-A-Cl, and RBC-OH-Fe recorded a spectacular rise in CEC and AEC over RBC-W. All the engineered biochar remarkably reduced the leaching of NH4+-N, NO3- -N, PO43--P and K+ from a sandy loam soil and increased retention of these nutrients. RBC-O-Cl at 4.46 g kg-1 dosage emerged as the most effective soil amendment increasing the retention of above ions by 33.7, 27.8, 15.0, and 5.74 % over a comparable dose of RBC-W. The engineered biochar could thus enhance plants' nutrient use efficiency and reduce the use of costly chemical fertilizers that are harmful to environmental quality.

River water irrigation with heavy metal load influences soil biological activities and risk factors.

The Yamuna is one of the most polluted rivers in India and the land adjacent to river flowing through Delhi city is widely irrigated with its water for growing various food crops. Present study was undertaken to assess the heavy metal load in Yamuna water and surrounding soils of the river bank and its impact on soil enzyme activities. Long term impact of irrigation by Yamuna water on the activities of various soil enzymes namely dehydrogenase (DHA), urease (UA), fluroscein diacetate (FDA), aryl sulphatase (ASA), nitrate reductase (NRA), microbial biomass carbon (MBC) and potentially mineralizable nitrogen (PMN) were assessed. The sensitivity of soil enzymes to heavy metals were observed as DHA>UA>ASA>NRS. Total organic carbon, easily oxidisable soil organic carbon, available phosphorus and available potassium in different sites varied significantly. Total heavy metal contents in soils showed a decreasing order: Fe>Mn>Zn>Cr>Ni>Cu>Pb>Co>As>Cd and the DTPA extractable heavy metal contents followed the order: Mn>Cu>Pb>Zn >Fe>Ni>Cd>Cr>Co>As. Potential ecological risk factors (Er) were under low risk and comprehensive potential ecological risk indices (Ri) were found to be under low, moderate and high risk categories. Copper (Cu) is the main pollutant contributing considerable load to Ri. From (Ri) principal component analysis and cluster analysis, it is evident that the Okhla site (S8) is most contaminated. The water from Yamuna river needs to be cautiously used for growing various food crops on land adjacent to the river as its long-term usage might cross the permissible limits of heavy metals in the soil.