The Potassium Speciation and Bioavailabilityin Agricultural Soil and Plant
| Autor: | Chakkrit Poonpakdee, 彭查禮 |
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| Rok vydání: | 2018 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 Potassium (K) is a macro-nutrient for plant growth. The bioavailability of K depends on its speciation distribution in the soil. Wet chemical extractions are commonly used to estimate K speciation including traditional single leaching (TSL) and sequential extraction process (SEP). In wet chemical extraction, the soil requires pretreatment, chemical preparation, and the experiment needs to be conducted using specific methods and under specific conditions. The synchrotron light sources technique (X-ray absorption spectroscopy, XAS) has a number of advantages: It is non-destructive to the sample and gives a direct estimation of the component in the sample. Potassium speciations in soil exist in dynamic equilibrium. Moreover, clay mineral in soil is a factor that influences soil fertility. The change of the microstructure of clay minerals in various environmental conditions (such as swelling or shrinking) was characterized using Transmission X-Ray Microscopy (TXM). The objectives of this study were to 1) estimate K speciations 2) estimate soil K buffering power, and 3) investigate K transformation and translocation between soil K and plant K. The results showed that for the various SEP schemes, K speciation was found to be greatest in the residual fraction, with only 3% observed in the carbonate, exchangeable, metal organic complex, or amorphous hydroxides of Fe or Mn. After following the first two steps of the SEP schemes, the available K was similar to that of the TSL method. Distribution of non-exchangeable K using the TSL method was comparable with the five combined SEP extraction steps which were all affected by environmental conditions. Direct method demonstrated that soil samples showed potassium K-edge XANES peak at 3615.2 eV. This peak represented excitation of 1s electrons as the K orbital. Five types of soil samples fitted well with an illite-smectite standard that related to the soil component. Furthermore, the 2 and 3-dimensions of soil flocculation structure were successfully deconstructed and showed variations in structure. Soil available K (exchangeable, and carbonate fraction) is the K bioavailability fraction in soil. Soil cation exchange capacity (CEC) and K desorption rate had a positive correlation with the amount of K translocation to plant and water leaching K. The ration between K transformation to plant and water leaching K found that K loss was at 1 A.U. per 5-15 A.U. to plant in soil applied K fertilizer and 9-44 A.U. in soil that was not treated with K fertilizer. Exchangeable K (24-30%), carbonate K (20-75%), and easily reducible metal oxide K (1.70%) were the sources for K translocation from soil to plant K and water leaching K. Plant growth in soil applied with K fertilizer was higher than that grown in soil that had no K fertilizer applied (shoot height 1.28-1.31 folds; dried weight 1.29-1.35 folds; total plant K 1.52-2.39 folds). Wet chemical extraction from SEP is highly advantageous to classify the soil K speciation that is correlated with K bioavailability as total plant dried weight (r2 = 0.71), plant shoot height (r2 = 0.65), and shoot dried weight (r2 = 0.71). Therefore, a combination of direct and indirect methods for measuring K speciation in soil is the most effective method to provide more information and the relationship between soil K speciation information in large and atomic scale. |
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