S. C. Datta

Changes in Nutrient Status During Preparation of Enriched Organomineral Fertilizers Using Rice Straw, Low‐Grade Rock Phosphate, Waste Mica, and Phosphate Solubilizing Microorganism

An experiment was carried out to study the changes in nutrient contents during preparation of enriched organomineral fertilizers using rice straw, low‐grade rock phosphate (RP), waste mica, and phosphate‐solubilizing microorganism (Aspergillus awamori). Composting reduced the total carbon (C) but increased total nitrogen (N) content with the progress of composting. This was reflected in the decrease of the C/N ratio. Significant increases in total phosphorus (P) and potassium (K) were also observed where both RP and waste mica was added along with Aspergillus awamori. Ammonium N (NH4 +‐N) decreased while nitrate N (NO3 −‐N) increased at the end of composting. Olsen P content increased up to 90 days, thereafter decreased up to day 150, whereas ammonium acetate K (NH4OAc‐K) increased gradually with the progress of composting. The study thus revealed that crop residue could be converted into a value‐added product through composting technology using low‐grade rock phosphate and waste mica along with phosphate‐solubilizing microorganisms.

Interrelationship of pH, Organic Acids, and Phosphorus Concentration in Soil Solution of Rhizosphere and Non-rhizosphere of Wheat and Rice Crops

To study the interrelationship of pH, soil solution phosphorus (P) and organic acids concentrations in rhizosphere and non-rhizosphere of wheat and rice, plants were grown in plastic funnels (150 mm diameter) containing 500 g of three types of soils, namely, Alfisol, Vertisol, and Inceptisol under greenhouse conditions. Soil solutions were collected by water displacement methods, 21 and 50 days after sowing. Eight different organic acids, viz., valeric, malic, benzoic, tartaric, citric, oxalic, acetic, and butyric were identified and quantified in rice rhizosphere. On the other hand only five (malic, tartaric, benzoic, citric, and butyric) acids were found in wheat rhizosphere. Organic acids were found to be more in rhizosphere and at initial stages of crop growth (21 DAS). Most of the acids showed negative relationship with solution P concentration, which indicated more secretion of organic acids from roots in P stressed condition in soil. Due to higher dissolution capacity of citric acid from non-labile P from soil constituents showed a positive relationship with soil solution P in both the crops in Vertisol. More occurrence and greater interrelationship of organic acids with P concentration were found in Alfisol having relatively lower pH and less solution P concentration.

Fractionation and colorimetric determination of boron in soils

We attempted to modify and evaluate existing sequential fractionation schemes for B involving the use of chemicals, which subsequently do not interfere with the measurement of B by colorimetry. Also evaluated was the contribution of various soil B fractions to the amount of B extracted by hot CaCl2, CaCl2-mannitol, salicylic acid, ammonium acetate, HCl, and tartaric acid. For this purpose, 17 soils with diverse properties were used. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl2, 0.05 M KH2PO4, 0.175 M NH4-oxalate (pH 3.25), 0.5 M NaOH, and HF + H2SO4 + HClO4. The procedure of elimination of color from extracts of oxide bound, organically bound, and residual B fractions was also evolved. Relationships of individual B fractions with physicochemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme. The relationships of different B fractions with extractable B in soils suggest that hot CaCl2 and salicylic acid may be better extractants for available B in soils. Fraktionierung und colorimetrische Bestimmung von Bor in Boden Ein bestehendes sequenzielles Fraktionierungsverfahren fur Bor in Boden wurde in Anbetracht des Fehlens eines ICP-Gerates modifiziert, um B colorimetrisch mit Azomethin-H und Carmin bestimmen zu konnen. Hierzu mussten auch Verfahren zur Eliminierung der Eigenfarbung der Bodenextrakte entwickelt werden. Das hier vorgestellte Extraktionsschema differenziert in (i) leicht losliches B, (ii) spezifisch adsorbiertes B, (iii) oxid-gebundenes B, (iv) organisch gebundenes B und (v) Residual-B. Insgesamt 17 verschiedene Boden wurden auch jeweils mittels heiser CaCl2, CaCl2 mit Mannitol, Salicylsaure, Ammoniumazetat, HCl und Weinsaure extrahiert und das so extrahierte B den oben genannten B-Fraktionen zuzuordnen versucht. Aufgrund der gefundenen Beziehungen wurden heises CaCl2 und Salicylsaure als die geeigneten Extraktionsmedien fur pflanzenverfugbares B in Boden ermittelt.

Effect of citric acid treatment on release of phosphorus, aluminium and iron from three dissimilar soils of India

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 soils viz. 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−1 CA 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−1 dose released the highest P, 0–20 mg L−1 dose was observed to be economical and 5 mg L−1 was the most promising dose in Alfisol.

Effect of partial removal of adsorbed humus on kinetics of potassium and silica release by tartaric acid from clay–humus complex from two dissimilar soil profiles

The aim of this investigation is to study how adsorbed humus on clay minerals affects kinetics of dissolution of clay mineral by an organic acid in terms of K and Si release. Clay–humus complexes were isolated from soil samples collected from different depths of 2 soil profiles from an Inceptisol of North India under long-term rice–wheat and maize–wheat cropping systems. Clay–humus complexes were subjected to repeat extraction with 100 mg/L of tartaric acid solutions before and after removal of humus with 30% hydrogen peroxide and the resultant release of potassium and silica was measured. Before removal of humus, K release followed Elovich kinetics for the maize–wheat cropping system.For the rice–wheat cropping system, except surface soil, which followed Elovich kinetics, other subsurface soils followed the power form of kinetic equations. But when humus was partially removed, K release increased exponentially, therelease rate increasing with time. This indicated that for humus-depleted clay, initial release triggered further release of K. Silica was released at a constant rate. The dissolution reaction was incongruent, i.e. the amount of constituents released in solution was not proportional to their mole fraction present in the mineral. X-ray diffraction analysis showed that micaceous mineral was partially dissolved and vermiculite was completely dissolved when humus was partially removed from clay before extraction. This observation indicates that humus adsorbed on clay plays an important role in preventing clay dissolution by organic acids.

Relationship between Phosphorus Sorption and Soil Acidity as Affected by Bicarbonate and Silicate Ions

Abstract The aim of this article was to establish a relationship between phosphorus (P) sorption and pH and phosphorus concentration of soil solution in the presence of specifically sorbed anions such as bicarbonate and silicate. Phosphorus sorption isotherms were obtained at different pH values of equilibrated soil solutions for three surface soil samples, namely Typic Haplustept, Calcic Chromustert, and Ultic Paleustalf, in three different systems, namely bicarbonate (0.001 M), silicate (0.001 M), and a system without any bicarbonate and or silicate, all having a common concentration of 0.1 M sodium chloride (NaCl). Phosphate sorption data at different pH values could be fitted very closely to a modified Freundlich equation of the form X/m=K Ha Cb, where, X/m is the amount of phosphate sorbed at solution phosphate concentration C and hydrogen ion concentration H. The values of a and b were positive fractions found to vary with soils and ionic medium. A silicate system more effectively reduced P sorption, particularly at lower pH values. The differences in P sorption in different media gradually decreased in all the soils as pH increased.

Characterization of Soil for Potential Potassium Supplying Capacity and Release of Non‐exchangeable Potassium During Cropping Through Simulation Model

Abstract An attempt has been made to develop a method to characterize soils with respect to potential potassium (K) supply capacity and release of non‐exchangeable K during cropping and its contribution towards K uptake through a simulation model. The model is based on the equation of continuity (a mathematical statement derived on the basis of principle of conservation of mass of solute and water in a soil element) with the assumption that nutrient flux from soil to root proceeds by mass flow and diffusion and influx into root follows Michaelis–Menten kinetics. Potassium fixation or release in soil has been simulated by incorporating a sink and source function, respectively, to the equation of continuity with the hypothesis that K release takes place in soil when labile K level goes below release threshold level (RTL) and fixation takes place when labile K level goes above fixation threshold level (FTL). Different soil and root parameters required for this model have been determined in solution culture and pot culture experiment, and a computer program has been written in visual basic to run the model. The model was run to characterize a soil with respect to its maximum supply of K to wheat crop from different depths and the contribution of non‐exchangeable K, therein, and compared with the data of a field experiment. It has also been shown by simulation that maximum response towards applied K occurs at a particular value of available K, which shifts towards higher value as RTL increases.

Threshold levels of release and fixation of phosphorus: Their nature and method of determination

Methods have been developed to show that two different levels of phosphorus (P) concentration in soil solution exist, termed Threshold Level of P Release (RTL) and Threshold Level of P Fixation (FTL). While labile P content of the soil increased sharply below RTL, it decreased sharply when P concentration increased beyond FTL. In the case of Ustochrept FTL was stable but in that of Chromustert and Plinthaqualf, FTL was found to be metastable. It was observed that once fixation starts beyond FTL, it continues even after P concentration drops below FTL, which has been explained on the basis of supersaturation and precipitation of solution P. The values of RTL and FTL were found to be dependent on bicarbonate concentration of soil solution.

Interrelationship of Organic Acids and Aluminum Concentrations in Rhizosphere and Nonrhizosphere Soil Solution of Rice in Acidic Soil

To study the interrelationship of organic acids and aluminum concentrations in rhizosphere and nonrhizosphere soil solution of rice (var. Satabdi and IR 64) in acidic soil, plants were grown in plastic pots containing 500 g soil. Three organic acids (viz., tartaric, oxalic, and citric acids) were identified and quantified in rice rhizosphere and nonrhizosphere soils. Organic acids were found more in the rhizosphere soil and at early stages of crop growth, decreased sharply after 30 days of germination, and found in negligible quantity after 45 days of germination. Regression analysis revealed a significant and negative relationship between solution aluminum and organic acid. Satabdi showed greater organic acid concentration in rhizosphere soil, leading to significantly lower root and shoot aluminum concentrations and consequently significantly greater dry-matter production as well as root volume, compared to IR 64. The findings established that organic acids can effectively reduce aluminum concentration in soil solution.

Assessing Stability of Humus in Soils from Continuous Rice-Wheat and Maize-Wheat Cropping Systems using Kinetics of Humus Desorption

To assess soil quality with respect to carbon sequestration, one should know not only the amount of carbon present in soil but also the strength with which the carbon is held to the mineral surfaces. A chemical method based on batch desorption of adsorbed humus on clay humus complex by sodium hydroxide–sodium pyrophosphate solution was used to assess the stability of humus carbon using soils from two systems of continuous cropping such as rice-wheat and maize-wheat. Humus desorption data were found to be very closely fitted to a linear combination of three first-order equations indicating three different pools of carbon. Humus retention was found to be related to poorly crystalline smectites. Rice-wheat system showed greater contrasting difference in humus stability than maize-wheat system along the depth of the soil profile.