Soil maturity assessment in indo-gangetic alluvium of bihar using soil inorganic phosphorus fractions based weathering index: A comparative approach

Abstract

Different forms of inorganic soil phosphorus (P) were characterized in relation to soil properties in four pedons belonging to order Inceptisols occurring in sub-tropical agro-climatic zone III of Bihar, falling under Indo-Gangetic alluvium region of Patna district. The soil of the Indo-Gangetic alluvium are clay loam to clayey in texture, neutral to alkaline in reaction (pH 7.3-8.0) having high electrical conductivity (EC) i.e. high amount of soluble salts in soil solution. The available P content in soils of the region was low to medium range (4.13 – 13.6 mg kg-1). The organic carbon (OC) content of the region was medium (0.20 -0.65%). Based upon weighted mean (PWM) values maximum amount of P is in the form of calcium-P (Ca-P) [38.8 mg kg-1] while minimum amount of P is in the form of iron P (Fe-P) [5.16 mg kg-1] contributing 50.4 and 6.7% of total inorganic P content, respectively. The sequential extraction of inorganic soil P fractions reveal that the mean relative abundance follow the order: Ca-P (50.4) > Saloid-P (14.3%) > Occluded-P (11.8%) > Reductant-P (9.4%) > Al-P (8.2%) > Fe-P (6.7%). The PWM total P content suggested that the soils are fairly rich in P reserve ranging from 129.3 – 371.1 mg kg-1 with overall mean of 138.7 mg kg-1. The available P showed positive significant correlation with Fe-P (r = 0.58**), Ca-P (r = 0.58**) and total-P in the soil profile indicating their contribution in P availability in the area. The total P showed positive significant correlation with Al-P (r = 0.74**), Ca-P (r = 0.63**), and organic-P (r = 0.74**), indicating their dominance in contribution of P pool of the area. Maturity sequence derived from weathering index (WI) based upon inorganic soil P fractions is: P1 (most matured) > P2 > P4 > P3 (least matured). Hence, pedon-1 was found to be most matured while pedon-3 was least matured is good agreement with that obtained from soil classification indicating a close relationship between the former and the later. This study emphasized that the active form of P converts into saturated P-fractions in the soil leading to the increase in the availability of various P forms on addition of proper P-fertilizer. The inorganic soil P based weathering index is proved to be a very suitable and extremely useful index for predicting soil maturity of this region. © 2016, IndianJournals.com. All rights reserved.