Anionic equilibria in major soil types of Kerala
| dc.contributor.advisor | Sureshkumar, P | |
| dc.contributor.author | Reshma M R, M R | |
| dc.contributor.author | KAU | |
| dc.date.accessioned | 2021-08-13T09:39:11Z | |
| dc.date.available | 2021-08-13T09:39:11Z | |
| dc.date.issued | 2020 | |
| dc.description | PhD | en_US |
| dc.description.abstract | Soils formed under tropical humid climate of Kerala are one of the best to study about chemistry of anions. Twenty two representative soil samples were collected from 7 different agro-ecological units of Kerala with wide variation in organic matter content and texture. The study aimed to understand the relative adsorption of selected anions on soil solid phase and to know the competitive interaction of fractions of these anions with respect to their adsorption behavior and bio-availability and the relative intensities of each of these anions. Out of the 22 samples collected, 5 samples were in near neutral pH, all others were acidic. Low lands of Pokkali, Kole and Kuttanad showed high organic carbon status. In general, sandy soils from northern coastal plain and Onattukara sandy plain were low in fertility and low land soils of Pokkali, Kole and Kuttanad were high in fertility. XRD data revealed the dominance of kaolinite mineral in all the representative soils except the soil from Palakkad eastern plain. Fractionation of phosphorous, sulphur, boron and silicon was carried out to know the major fractions and its contribution to the available pool. Dominance of P fractions was different in different types of soil. Saloid - bound phosphorous is contributing least to the total P content. All the S fractions were high in Pokkali soil. The percentage contribution of different fractions of Si to the total Si were in the order; residual Si > amorphous Si > occluded Si ≈ organic Si > adsorbed Si> mobile Si. The percentage contribution of different fractions of B to the total B were in the order; residual B > organically bound B > oxide bound B> readily soluble B > specifically adsorbed B. Among all the fractions, readily soluble and mobile fractions are the major contributor to the available pool. Single anion adsorption experiments were conducted for nitrate, P, S, B, Mo and Si at 250C and 400C. Quantity - intensity relations and thermodynamic parameters were worked out based on the adsorption data. Freundlich, Langmuir and Tempkin isotherms were fitted using the adsorption data. Dominance of desorption was observed in case of Si and S, with added concentration of these elements. Whether it is adsorption or desorption, the process was spontaneous in most of the soil for all anions under study. Q-I curve of these elements showed reduction in desorption after reaching a maximum desorption, indicating the possibility of adsorption on further addition of higher concentration of these elements. Adsorption of B was less because only lower concentration of B was used in adsorption study and the existence of non-ionised forms of B at the acidic equilibrium solution pH. Due to these reasons adsorption of B, S and Si was found less than nitrate adsorption. P and Mo showed very high similarity in adsorption behavior with high affinity of these elements to the adsorption sites, which is due to the inner-sphere complex formation by these elements. Increase in buffer power and maximum quantity adsorbed with added concentration of P and Mo was observed especially in low land soils of Pokkali, Kole and Kuttanad indicating the chemical nature of adsorption. Freundlich adsorption isotherm was the best to explain adsorption of anions in soil followed by Tempkin and Langmuir adsorption isotherm, which implies that the bonding energy of the adsorbate anion on the soil surface decreases with the fractional coverage of the adsorbent surface. Among P and Mo, the constants related to strength of adsorption were high for Mo adsorption than P adsorption. Kaolinite, hematite, goethite, other oxides and hydrous oxides of Fe and Al are the major sites for anion adsorption. Preferential adsorption of phosphorous over boron was observed in all soils in adsorption study conducted with binary system of P and B. Using P, for estimation of AEC can lead to the overestimation due to the specific adsorption behavior of P. A general trend in silicon extractability of different extractants was in the order; Bray I reagent > CBD > 0.5M acetic acid > 0.1M HCl. The possibility of over estimation of P due to the interference of Si in molybdenum blue colorimetric estimation was observed at high concentration of Si. Greater than 10 per cent over estimation was observed if Si:P ratio is greater than 80. | en_US |
| dc.identifier.uri | https://krishikosh.egranth.ac.in/handle/1/5810171876 | |
| dc.keywords | Soil Science and Agricultural Chemistry | en_US |
| dc.language.iso | English | en_US |
| dc.pages | 301p. | en_US |
| dc.publisher | Department of Soil Science and Agricultural Chemistry, College of Horticulture, Vellanikkara | en_US |
| dc.sub | Soil Science and Agriculture Chemistry | en_US |
| dc.theme | major soil types of Kerala | en_US |
| dc.these.type | Ph.D | en_US |
| dc.title | Anionic equilibria in major soil types of Kerala | en_US |
| dc.type | Thesis | en_US |