Soil quality under different agricultural land uses as evaluated by chemical, geochemical and ecological indicators in mountains with high rainfall (Darjeeling Himalayas, India)

Abstract

PurposeAgricultural land use associated with intensification in plant growing affects the physicochemical parameters of soils and thus soil quality. The aim of this study was to identify the quality of soils in the Peshok catchment in the Eastern Himalayas under different types of land use (tea, horticulture, rice), under high monsoon rainfall conditions.MethodsPhysical and chemical analysis were used, e.g. bulk density, pH, TOC, major and trace element content (such as Ca, Fe, K, Mg, Mn, Na, P, Ag, As, Ba, Cd, Co, Cr, Cu, Ga, Li, Mo, Ni, Pb, Sr and Zn) based on AntonPaar Multiwave 3000 microwave system and nitrogen and sulphur content using CNS Elementar Vario MAX cube analyser. In addition, ecotoxicological analyses were performed using the Microtox test. Soil quality was assessed on the basis of chemical indicators related to the mobility of trace elements (risk assessment code, individual contamination factor and global contamination factor); geochemical indicators (geoaccumulation index, enrichment factor, contamination factor, contamination degree, modified contamination degree, pollution load index and improved Nemerow pollution index); and ecological indicators (potential ecological risk coefficient and potential ecological risk index). A statistical package of Statistica v13 was used for statistical analysis.ResultsSoils in the analysed catchment are characterised by low contents of macro- and microelements. It was shown that natural factors, such as high precipitation and steep slopes, favour strong leaching of elements from the soil, and farming systems based on natural and chemical fertilisation, terracing and irrigation are not able to balance them fully. The contents of TOC and N as well as pH were determined mainly by the land use. Results of statistical analyses and geochemical indicators revealed the predominantly natural origins of elements. The higher Ga content indicated a relationship with the local geology and the higher Cu content with the use of fertilisers. Indicators showed a low ecological risk related to the presence of trace elements, and soil ecotoxicity to A. fischeri was generally determined by the acidic pH of the tested soils. Low mobility was observed for most elements, and regardless of the land use, the residual fraction predominated.ConclusionThe study showed that use of many indicators can more fully describe soil quality in relation to land use, especially in the case of a low content of trace elements. Moreover, this approach helps to better understand the changes taking place in soil quality under different land uses in mountains with high rainfall.