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Subject: Soil Sciences × Author: Borah, Supriya × End date: 2018 × Start date: 2018 × Type: Thesis ×
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    ThesisItemOpen Access
    ALUMINIUM AND PHOSPHATE POTENTIAL IN ACID SOILS OF ASSAM
    (AAU, Jorhat, 2018) Borah, Supriya; Bhattacharyya, Devajit
    The study was carried out to investigate the “Aluminium and Phosphate Potential in Acid soils of Assam”, with the objectives 1) Determine different form of aluminium and phosphorus in Upper Brahmaputra Valley Zone (UBVZ) of Assam and 2) Determine aluminium and phosphate potential in soils of UBVZ of Assam. For this study twenty (20) surface (0-15 cm) soil samples were collected from Sivasagar, Golaghat and Majuli district of Assam. The soils were analyzed for different parameters pertaining to this investigation following standard procedures and laboratory protocols. The soils were varied widely in texture (sandy clay loam to clay), clay content (13 - 40%), pH (H2O) (4.02-7.49), pH (KCl) (3.10 to 6.89), OC (0.59-2.85%), CEC (6.75 to 12 cmol (p+) kg-1), free oxides of iron (3.78 to 1.09%) and aluminium (1.17 to 0.32%), lime potential (3.04 -5.85). The results on forms of acidity revealed that TPA (7.05 cmol (p+) kg-1) was the most dominant form of acidity in soils UBVZ of Assam followed by PDA (5.13 cmol (p+) kg-1), Ext.A (3.16 cmol (p+) kg-1), TA (1.92 cmol (p+) kg-1) = Ex.A (1.92 cmol (p+) kg-1) and Non Ex.A (1.22 cmol (p+) kg-1). Among the forms of Al, the CBD extractable aluminium (Ald) was found to be the most dominant followed by oxalate extractable Al (Alo), weakly organically bound Al (Alw), totally organically bound Al (Alp) and exchangeable Al (AlKCl), with mean values 0.38,0.22, 0.09, 0.02 and 0.01per cent, respectively. The amorphous form of aluminium showed dominance over the crystalline form of aluminium. The Organic phosphorus of the soils ranged from 164.68 to 345.62 mg kg-1. Different inorganic P fractions of the soils were found in the order: Fe-P (68.2-20.4 mg kg-1) > Al-P (42.9-19.7 mg kg-1) > Occl-P (20-11 mg kg-1)>Ca-P (10.2-17.6 mg kg-1) > Re-P (15.6-9.2 mg kg-1)> Sal-P (2.3-10.2 mg kg-1). The percent release Al (%RelAl) decrease with increase in added Al irrespective of the soil studied. The highest and lowest %RelAl was observed in soil S4 of Sivasagar district and soil M3 of Majuli district, respectively. The decrease in %AdsP was ranged from 97.6 to 7.00 per cent in soils of UBVZ of Assam when addition of P was ranged from 1 to 5 mg l-1. The highest % AdsP was found in soil S1 of Sibsagar district, with a mean value of 97.11 per cent. The lowest mean % AdsP (15.98 %) was found in soil UM6 of Majuli. P released was observed at equilibrium solution of soil S8 of Sivsagar district and soil M3 of Majuli district at the lowest concentration of add P i.e. 1 mg l-1. In soil UM5 and UM6 of Majuli district % RelP was observed from 1 to 3 mg l-1 of add P. In all these soils % RelP was decreased with increased in addition of P. The mean value of % RelP in soils of UBVZ ranged from 20.64 to 30.89 per cent. The soil UM5 (24.32) of Majuli district had the highest aluminium potential and the same was the lowest in soil S4 (16.08) of Sivsagar district. Equilibrium aluminium potential (EAP) of the soils showed very high significant positive correlation with pH (H2O) and pH (KCl) (r=0.865** and r=0.735**) and very significant negative correlation with oxides of iron and aluminium (r=-0.819** and r=-0.850**). EAP of the soils also had negative correlation with all forms of acidity and exchangeable aluminium. The highest phosphate potential was observed in soil S1 (5.30) of Sivsagar district while lowest was observed in soil UM5 (0.70) of Majuli district. In these soils equilibrium phosphate potential (EPP) had a significant negative correlation with soil pH (H2O) (r=-0.956**) and pH (KCl) (r=-0.858**), and significant positive correlation with oxides of iron (r=0.938**) and oxides of aluminium (r=0.963**). Significant positive relationship of EPP was also observed with all forms of acidity except non exchangeable acidity. While a significant positive correlation was observed with Fe-P (r=0.791**), Al-P (r=0.733**), Occl-P (r=0.930**) and RS-P (r=0.500*). However, EPP of the soils had significant negative relationship with Org-P (r=-0.560**), Ca-P (r=-0.849**) and Sal-P (r=0.857**). The correlation of EPP with EAP and lime potential (LP) of the soils was significant and negative (r=-0.969** and r=-0.872**), respectively. In soils of UBVZ of Assam if EAP and LP were high the equilibrium phosphate potential will be low indicating higher availability of phosphorus, as increase of LP and EAP also increase the pH of the soils. Therefore, liming and addition of organic matter might be considered good management practices for these acid soils to increase the pH as well as to increase the Phosphorus availability.