Effect of land use patterns on size distributions and aggregates stability in the mountainous areas of north-western Himalayas, India

Abstract

A study was conducted to assess the impact of different land uses and management on soil aggregate stability in sub-mountainous area of Jammu state, India. Soil samples were collected from five different land uses systems viz., forest, horticulture, agriculture, pasture and degraded lands from each of the five locations for surface (0-15cm) and sub-surface (15-30cm) of soil depth. Soil aggregate stability was determined by dry and wet sieving methods. Dry sieving was determined without immersion in water and wet sieving was immersion in water, respectively. Soil properties such as soil organic carbon (SOC), bulk density (BD) and soil pH were also determined. Average soil organic carbon (SOC) content was observed to be higher in pasture (6.65 g kg-1) followed by forest (6.50 g kg-1), horticulture (5.76 g kg-1), agriculture (4.88 g kg-1), and degraded land (4.47 g kg-1). Soil BD was observed significantly higher in degraded land than in other land use, which was further increasing in deeper soil profiles. Macro aggregates (>2 mm) were abundant (52.52-91.13%) in pasture soils while micro-aggregates (<0.25 mm) were abundant (23.39-35.51%) in agriculture lands. Mean weight diameter (MWD) decreased significantly with immersion in water for soil depth for various land use indicating that the soils were vulnerable to water erosion. The influence of cultivation was generally expressed by reduced water stability aggregates (WSA) of soil aggregates, hence rendering the soil more vulnerable to crusting and erosion processes. Mean weight diameter (MWD) was dominant in pasture in surface soil whereas subsurface soil was dominant in forest landuse systems. The MWD from dry structure stability (GMDd) and their corresponding wet Mean weight mean diameter (MWDw) were related significantly (r = 0. 0.999**). The difference in the MWD in dry condition and immersion in water reveals that for degraded land was subject to severe degradation compared to cultivated, agriculture and horticulture soil, while for pasture land was more degraded than forest soil. The vegetation grown soils were of better soil structural quality than degraded land or no scanty vegetation. To preserve good structure thereby reducing soil degradation, long term fallows or other farming practices that ensure maintenance of soil organic matter.