Boron fractions and its availability in soils of the Indo-Gangetic plains

Abstract

We studied relationships between available B and different fractions of B in soils, and how soil properties, climatic parameters, and cropping systems influenced their contents in soils of the Indo-Gangetic Plains (IGP). Available B in soils was assessed by four methods viz., hot-calcium chloride (HCC), mannitol-calcium chloride (MCC), hydrochloric acid (HCl) and salicylic acid (SA). Soil B was also separated into five fractions viz., readily soluble B (RSB), specifically adsorbed B (SAB), organically bound B (OrB), oxides bound B (OxB) and residual B (RB). On average, a higher amount of available B was found in soils of the upper and trans region of IGP dominated by illitic minerals compared with a lower amount in the lower region dominated by kaolinitic one. Among the fractions, RB constituted ∼ 89 % of the total, followed by OxB(6.11 %) > OrgB (5.32 %) ≫ SAB (0.46 %) > RSB (0.26 %). Variations in the amount of available B, and its fractions in soils were explained on the basis of variations in soil properties and climatic parameters. For example, most of the fractions of B (SAB, OrgB and OxB) along with its available amount decreased with increasing soil depth due to declining contents of organic C and amorphous Fe- and Al-oxides. Soil properties explained 51–76 % variability in available B, and 27–65 % in different B fractions. Rice-based cropping systems mobilized RB to available (RSB and SAB) and potentially available (OxB and OrgB) fractions. Among the methods used, HCC and MCC were found suitable for assessing available B status in the soils. The study thus explained variations in B availability in rice and non-rice-based cropping systems, predicted its availability, and also identified suitable method(s) for its estimation in soils of the IGP for a better B management.