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Novel starch grafted zincated nanoclay polymer bio-composites (SZNCPBCs) were synthesized with variable percentages (8%, 10%, and 12%) of clay and nanoclay, acrylic acid, and acrylic amide as monomers, N,N-Methylene bisacrylamide (NNMBA) as crosslinker and ammonium persulfate (APS) as initiator. Clays, as well as SZNCPBCs were characterized viz. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR). Nanocomposite containing 12% nanoclay showed the slowest release rate. However, 8% clay containing nanocomposite recorded higher Olsen-P content and equilibrium water absorbency. SZNCPBCs proved to be an innovative controlled release Zn fertilizer formulation. [ABSTRACT FROM AUTHOR]

Abstract Studies to evaluate the release threshold level of potassium in Vertisols (shrink-swell soils) in different agro-ecological regions of India and how that may help in K fertility interpretations are rare. Thus the objectives of this study were (i) to evaluate the K status of Vertisols through release threshold levels and (ii) to relate the findings with soil K release and fertilizer management. Three established soil series samples were collected from Vertisols of different agro-ecological regions of India. Release threshold level (RTL) was assessed after equilibrating soil with 0.01 M CaCl 2 solution having series of soil: solution ratio, after which the remaining amount of exchangeable K was extracted with 1 N NH 4 OAc (pH 7). Total amount of K extracted (K T = K desorbed in CaCl 2 solution plus K extracted with 1 N NH 4 OAc) remained more or less constant with decreasing K-level up to a certain value (say threshold value) below which K T increased sharply indicating K release from non-labile form. The threshold value in terms of K concentrations (Release Threshold Concentration) of Panjari, Nagpur, Maharashtra (Typic Haplusterts, Sub-humid dry), Teligi, Bellary, Karnataka (Sodic Haplusterts, Semi-arid dry) and Kheri, Jabalpur, Madhya Pradesh (Typic Haplusterts, Sub-humid moist) soils were 0.044–0.049, 0.034–0.062 and 0.043–0.11 mm, respectively. The high release threshold K levels in terms of concentration and activity ratio (AR) were observed in soils of Teligi and Kheri series as compared to soils of Panjari series due to high content of trioctahedral mica in the former two soils. The relationships between clay minerals, release threshold level, exchangeable potassium and non-exchangeable potassium determined by 1 N HNO 3 and sodium tetra-phenyl borate (NaBPh 4) have been discussed. Highlights • Vertisols represent fertile lands and have vast geographical distribution in India. • Optimization of the efficiency of K requirement is a significant contribution to management of K fertilizer. • Knowledge of critical threshold value of K release in Vertisols for imminent loss of K due to fixation from added K. [ABSTRACT FROM AUTHOR]

Series of chitosan grafted zinc containing nanoclay polymer bio-composites (CZNCPBCs) with variable percentage (8%, 10% and 12%) of clay and nanoclay were synthesized by a novel method. Clays as well as CZNCPBCs were characterized through X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR). Release study of Zn 2+ from CZNCPBCs in Zn deficient soils revealed that combination having 12% nanoclay showed slowest release rate. Olsen-P content was found maximum in 8% clay containing composite. However, combination containing 8% clay recorded highest equilibrium water absorbency as well as moisture content at a particular tension. Inoculation with fungal species revealed that Aspergillus spp. was more effective as compared with Trichoderma spp. in evolution of cumulative CO 2 -C, indirectly indicating biodegradability. CZNCPBCs were found to be promising as controlled release (CR) Zn 2+ fertilizer formulation. [ABSTRACT FROM AUTHOR]

Nanoclays, which are active component of soils, play a very important role for enzyme adsorption. To study the effect of nanoclays on enzyme adsorption, these were isolated from three genetically different Indian soils, i.e. black soil (Vertisols), red soil (Alfisols) and recent alluvial soil (Inceptisols). Then X-ray coherent particle sizes of different nanoclays (with and without amorphous aluminosilicates) before and after acid phosphatase adsorption were studied. Result showed that basal spacing of smectite present in nanoclays increased due to intercalation of enzyme molecules, whereas ‘d’ spacing in kaolinite did not change due to enzyme immobilization. Average particle size, calculated by Scherrer equation, increased due to enzyme immobilization for all nanoclays. In case of kaolinite, enzyme molecules acted as linkers and bind more than one particle together, which resulted in increased apparent particle size. Crystallite size of kaolinite was also more than that of mica or smectite. Increased average particle size after enzyme immobilization was confirmed from transmission electron microscopy (TEM) images. [ABSTRACT FROM AUTHOR]

To evaluate different mathematical models for describing cumulative release of phosphorus (P), aluminium (Al) and iron (Fe) by citric acid (CA) from soil, an experiment was conducted in packed soil columns with three contrasting soilsviz.Alfisol, Vertisol and Inceptisol. The soils were saturated with CA at 0, 5, 10, 20, 40 and 100 mg L−1, the leachate were collected by liquid displacement at 15, 30, 45, 60 day intervals, and P, Al and Fe releases were analyzed. The release data were fitted to linear, quadratic, exponential, logarithmic, and power form of equations. The results revealed that the highest cumulative release of P, Al and Fe was observed in the 40 mg L−1CA treatment. In the majority of cases, the relationship between CA concentration and cumulative release of ions fitted well in quadratic equation (y = ax2 + bx + c). The Fe and Al releases with time were fitted well in power-form (y = atb), while the cumulative P release in linear equation (y = mx + c). The study also revealed that a substantial amount of released P could serve as potential source of plant nutrient in fixation prone soils. The study demonstrated that CA can be used as a ‘solubilizer’ of soil P, 40 mg L−1dose released the highest P, 0–20 mg L−1dose was observed to be economical and 5 mg L−1was the most promising dose in Alfisol. [ABSTRACT FROM AUTHOR]

• Arsenic adsorption from water using organically modified smectites was studied. • HDTMA-modified smectite showed the highest arsenic removal efficiency. • Organically modified smectites performed the best at an optimum pH = 6. • Ion exchange, electrostatic attraction and ligand exchange mechanisms were involved. Arsenic (As) poses a tremendous threat to human health due to exposure through arsenic-contaminated drinking water and/or food. We aimed to develop organically modified clay adsorbents for the removal of As from aqueous solution. We modified a smectite sample using three organic agents, namely hexadecyl trimethylammonium (HDTMA), chitosan and citric acid, and characterized the products using X-ray diffraction, infrared spectroscopy, and scanning electron microscopy techniques. The characterization techniques suggested successful organic modifications of the smectite sample. The surfactant-modified smectite was the most efficient (66.9%) As removing adsorbent with a maximum adsorption capacity of 473.2 μg g−1. Kinetic study showed that the adsorbents reached As adsorption equilibrium within 3 h, and the data fitted reasonably well to power function and simple Elovich equations (R2 > 0.89). The adsorption data were explained well by the Freundlich and Sips isothermal models. The surfactant-modified and chitosan-grafted organoclays adsorbed As by electrostatic attraction and anion exchange, whereas the citric acid activated smectite followed ligand exchange and simple anion exchange mechanisms. This study thus demonstrated the potential of surfactant-modified clays in removing As from contaminated waters. [ABSTRACT FROM AUTHOR]

This study assessed the effect of land use systems (rice-fallow, bamboo, mandarin and forest) along an altitude gradient (<500, 500–1000 and > 1000 m asl) and soil depth (0–15, 15–30 and 30–45 cm) on C stability in naturally occurring clay-organic complex (NOCOC) and their relationship with soil properties. The C stability in NOCOC (1/k) was determined from desorption rate constant (k) of humus-C by sequential extraction and was correlated with soil properties across the altitude. The C stability in NOCOC decreased (34%) with increasing soil depth from 0–15 to 30–45 cm. Across the altitudes, highest C stability in NOCOC was at > 1000 m asl (8.37 h) which was 12.7 and 9.4% higher than 500–1000 and < 500 m asl, respectively. Irrespective of soil depth and altitude, forest (5.30 h) showed the greatest C stability in NOCOC followed by mandarin (4.64 h), bamboo (4.20 h) and rice-fallow (3.85 h). Measurable soil properties could explain 90–94% variability of C stability in NOCOC across the altitude. Furthermore, C stability in NOCOC increased macroaggregate formation (0.25 mm) and ensured greater physical, chemical and microbial protection of organic C in soil. [ABSTRACT FROM AUTHOR]

The use of modified clay minerals for adsorbing arsenic (As) in contaminated soils is an underexplored area of research. The adsorption behavior of As onto inorganically modified smectite and kaolinite both in aqueous and soil media was studied. X-ray diffraction, infra-red spectroscopy, scanning and transmission electron microscopy studies confirmed successful modification of smectite through Fe-exchange and Ti-pillaring, and kaolinite through phosphate binding. The modified smectites were more efficient than phosphate-bound kaolinite in adsorbing As both in water and soil systems. Kinetic study revealed that the clay products reached adsorption equilibrium within 3 h, and the data well fitted to the power function and simple Elovich equation (R 2 > 0.90). The Freundlich isotherm model best described the As adsorption data (R 2 > 0.86) of the modified clay products in both the systems. The Ti-pillared smectite exhibited the highest As adsorption capacity (156.54 μg g − 1 ) in the aqueous medium, while the Fe-exchanged smectite was the best material in the soil system (115.63 μg g − 1 ). The partition coefficient (K d ) and adsorption efficiency (%) data also maintained the similar trend. Precipitation of As and binuclear complex formation also took place in the soil system which made the metalloid non-labile as the time passed. The inorganically modified clay products reported here hold a great potential to adsorb As in contaminated groundwater, drinking water as well as soil. [ABSTRACT FROM AUTHOR]

In order to enhance the efficiency of metal immobilisation, bentonite clay was pillared with polyhydroxy aluminium complexes. The pillared bentonite was systematically characterised by multiple techniques including x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The clay product was assessed for its metal removal efficiency from aqueous systems through batch experiments with variables in pH, amount of adsorbent and initial metal concentration. The adsorption data were fitted with Langmuir and Freundlich isotherm models. The maximum monolayer adsorption capacity of pillared bentonite was 61.4, 32.3 and 50.3 mg g − 1 for Cu (II), Zn (II) and Ni (II), respectively. The immobilisation efficiency of pillared bentonite was assessed by greenhouse pot culture experiment with amaranth as the test crop. Amendment of soil with pillared bentonite at 2.5% significantly improved the plant growth as well as reduced the bioavailable metals in the metal spiked soils. The study demonstrated that pillared bentonite could potentially be used for addressing heavy metal pollutions by immobilising the metals in the contaminated soil. [ABSTRACT FROM AUTHOR]

Due to rising health concern, the idea of Good Agricultural Practices (GAPs) has emerged, especially for growing crops organically. In this context, several innovative technologies have been developed by agricultural scientists, such as the particle film technology (PFT). They are basically aqueous formulations made from chemically inert clay or mineral particles, which are specifically formulated for coating to reduce the damage caused by insects, diseases, solar injury, freeze injury and to improve fruit finish, color, carbon assimilation rate, yield and postharvest fruit quality. The development of the first such kaolin-based formulation, named Surround®, for commercial use was by Engelhard Corporation, Iselin, New Jersey (U.S.A.) in 1999. During the last two decades, a significant amount of research work has been conducted on the development of several such films (Surround® CF, Surround® WP, Raynox®, Cocoon™, Purshade™, Parasol®, Screen®, Snow®, Eclipse™, etc.) and their effects on various agricultural and horticultural crops. Considering the usefulness of these films, we attempted to compile the scattered information on the developed particle films, their modes of action and effects on various horticultural crops, in the form of a review. The review is particularly focused on history, modes of action, application and a variety of effects of particle films on horticultural crops. [ABSTRACT FROM AUTHOR]

A series of bentonite polymer-composites (BPCs) loaded with metribuzin were studied for their controlled release in aqueous medium. The release of active ingredient from BPCs was significantly lower as compared to commercial metribuzin formulation. The results revealed that the cumulative metribuzin release was highest (81%) from the BPCs containing 8% clay (commercial bentonite) and 2% metribuzin which correspond to the lowest (14 days) half-life values i.e., time required for 50% release of active ingredient (t1/2). The metribuzin release from the BPCs decreased with increased concentration of clays in polymer matrix and the release was further decreased with BPCs prepared with pure nano-bentonite. BPCs containing 12% clay and 2% metribuzin showed maximumt1/2values i.e.,25 and 51 days for commercial bentonite and pure nano-bentonite as clay sources, respectively. The differential behaviour in the metribuzin release rates from BPCs was ascribed due to variations in crosslinking of metribuzin in the composites. As metribuzin release was found to be slower in BPCs compared to commercial formulation, it could be used for control of weeds tailored to different crops. [ABSTRACT FROM AUTHOR]

Majority of organic matter is bound to clay minerals to form stable colloidal organo-mineral fraction (COMF) in soil. Stability of carbon (C) in COMF is crucial for long-term C sequestration in soil. However, information on the effect of long-term fertilization and manuring with various organic sources on C stability in such fraction in soils with varying clay mineralogy is scarce. The present study was, therefore, carried out to assess the effect of thirty-one years of continuous fertilization and manuring with different organics on C-stability in COMF extracted from an Inceptisol, a Vertisol, a Mollisol, and an Alfisol. The treatments comprised of control (no fertilization), 100% NPK (100% of recommended N, P and K through fertilizer), 50% NPK+ 50% of recommended N supplied through either farm yard manure (FYM) or cereal residue (CR) or green manure (GM). The stability of C (1/ k) in COMF was determined from desorption rate constant (k) of humus-C by sequential extraction and correlated with extractable amorphous Fe-Al-Si-oxides, and crystallite size of illite minerals. Long-term fertilization and manuring with the above sources of organic altered the contents of amorphous Fe-Al-Si-oxides, and decreased the crystallite size of illite in all the soil orders. Fifty percent substitution of fertilizer N by various organics significantly increased C-stability in COMF by 27–221% (mean 111%) over full dose of NPK (100% NPK). Smectite dominating Vertisol exhibited highest stability of C followed by the Mollisol, the Inceptisol and the Alfisol. Stability of such C in soil was correlated positively with the amount of amorphous Fe and Al oxides but negatively with crystallite size of illite (r = −0.46, P < 0.01). Application of NPK + GM or NPK + FYM in Inceptisol, Vertisol and Mollisol and NPK + GM or NPK + CR in Alfisol emerged as the best management practices for higher stabilization of C in COMF for long-term C sequestration. Unlabelled Image • Long-term fertilization and manuring altered the C stability in COMF. • Amorphous Fe, Al oxides positively influenced the C stability in COMF. • Fertilization and manuring decreased the average crystallite size of illite. • NPK + GM was most effective in increasing C stability in COMF. [ABSTRACT FROM AUTHOR]

Abstract Fertilizer use in Indian agriculture is skewed towards nitrogen (N) and phosphorus (P), and farmers generally neglect potassium (K) input ignoring K requirement of crops. We, therefore, studied the long-term effect of imbalanced fertilization (i.e. without K) on K supplying capacity of a kaolinitic red soil (Typic Haplustalf) after 42 years of intensive cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 42 cropping cycles from an on-going long-term fertilizer experiment located at Birsa Agricultural University, Ranchi, India, from six treatments, viz. control (unfertilized), fertilizer N, NP, NPK, 150% NPK (1.5 times of NPK) and NPK + FYM (NPK + farmyard manure), along with adjacent uncultivated land. Soil K pools, clay minerals, quantity-intensity relationship and K release kinetics along with grain yield and K uptake of soybean and wheat were studied. Among the treatments, NP treated soils showed the lowest amounts of labile (K L) and non-exchangeable K (K nex). Equilibrium activity ratio (AR e K) and non-specifically held K (−ΔK 0) were also lowest under NP treatment. The gap between equilibrium exchangeable K (EK 0) and minimum exchangeable K (EK min) was minimum under NP. Cropping and fertilization-induced transformation in clay minerals was noticed wherein continuous neglect of K fertilizer led to a decrease in illite content with a concomitant increase in interstratified minerals. On the other hand, noticeably lower alteration in clay minerals and comparatively less depletion in overall K-supplying capacity of soil were recorded under K addition as compared to imbalanced fertilization (i.e. without K). Soybean showed a significant positive response to K application. The study thus underlined the necessity of adequate K input for the sustenance of soil health, inherent K-supplying capacity and crop productivity. Highlights • We studied long-term effect of cropping with or without K input on soil K-fertility. • Imbalanced fertilization with respect to K caused depletion of soil K pools. • Imbalanced fertilization adversely affected quantity, intensity and K release rate. • Continuous neglect of K addition led to distortion in clay minerals. • Cropping with K addition maintained much better K-supplying capacity of soil. [ABSTRACT FROM AUTHOR]

• Effect of long-term cropping on K supplying capacity of Inceptisol and Vertisol was studied. • K omission depleted K ex in both soils and NEK reserve in Inceptisol. • Cultivation without K adversely affected quantity, intensity and K release rate. • Cultivation with K input maintained relatively better K-supplying capacity of soils. • Existing K fertilizer recommendations appeared inadequate in both soils. Despite removal of potassium (K) by crops in large quantities, often exceeding that of nitrogen (N), K fertilization has long been neglected compared with N and phosphorus (P) in Indian agriculture leading to mining of soil K. We, therefore, studied the effect of long-term fertilization (with or without K) on K supplying ability of two major soil orders of India, viz. Inceptisol and Vertisol after more than four decades of cultivation. Soil samples (0–15 and 15–30 cm) were collected after the completion of 43 (Inceptisol) or 42 (Vertisol) cropping cycles from on-going long-term experiments located at New Delhi (Inceptisol) and Jabalpur (Vertisol), India, from six treatments, viz. no-fertilization (control), recommended N (N), N and P (NP), N, P and K (NPK), 150% NPK and NPK + farmyard manure (NPK + FYM), along with adjacent uncultivated land. Ammonium acetate extractable K (K ex), non-exchangeable K (NEK), quantity-intensity relationship and K release kinetics along with grain yields and K uptake by crops were studied. The K ex and K-saturation of exchange complex in both soils and NEK in the Inceptisol were the lowest under NP followed by N. Cropping without K input resulted in lower quantity (non-specifically and specifically held K i.e. –ΔK 0 and K s) and intensity (equilibrium activity ratio i.e. AR e K) of K in both soils. More negative values of standard free energy of exchange (ΔG0) under cultivation without K in both soils indicated increased affinity of soil solids for K+ owing to K omission. The gap between equilibrium exchangeable K (EK 0) and minimum exchangeable K (EK min) was significantly lower under cropping without K than with K in the Vertisol. Imbalanced fertilization (N or NP) also showed noticeably smaller cumulative K releases and slower rates of replenishment of solution K by solid phase K in both soils. Interestingly, even under cropping with K fertilization at either experimental site, several K supply parameters showed decline compared with adjacent uncultivated soil. Grain yields of wheat and total K uptake by all crops (maize and wheat in Inceptisol; soybean and wheat in Vertisol) showed significant and positive response to K application. The study showed variable effect of long-term intensive cropping with or without K input on the K supplying ability of an Inceptisol and a Vertisol. The findings underlined inadequacy of the existing K fertilizer recommendations, and the need for their refinement to minimize native K mining and sustain K supplying ability of soils. [ABSTRACT FROM AUTHOR]