Assessing soil properties and chemical quality indices under trees outside forests (TOFs) in temperate Himalayan region

Abstract

Trees outside forests (TOFs) have assumed importance in view of its potential to mitigate CO₂ under different carbon pools with soil as the prominent pool. The ability of any TOF practice to fix soil organic carbon (SOC) efficiently depends on its SOC build up and soil quality that varies across different strata within TOFs. Soil physico-chemical properties under six TOF practices (boundary plantation, roadside plantation, riverside plantation, horticulture, scattered patches with clumpy plantation (SPCP), and woodlot) in central region of Kashmir valley were investigated to assess SOC content and soil quality. Additive soil quality index (ASQI) approach was used to assess soil quality using "lower or higher is better" criteria. Correlation analysis between soil variables was carried out to assess the relationships. The results showed that TOF soils in the region were sandy clay loam in texture with slightly acidic to alkaline pH and electrical conductivity within normal limits. Lowest bulk density (0.94 g cm^-3) was found in SPCP and highest (1.38 g cm^-3) in roadside plantation. Highest SOC %, available nitrogen (N), and available phosphorus (P) values were observed in SPCP and lowest in boundary plantation. Average available potassium (K) was observed highest in SPCP (333.04 kg ha^-1) and lowest in riverside plantation (244.58 kg ha^-1). Soil pH showed significant but negative correlations with SOC and other nutrients (N and P). A significant but perfect positive correlation was observed between SOC and available N. SOC content was found highest in SPCP (60.16 t ha^-1) and lowest in boundary plantation (34.56 t ha^-1). The hypothesis that all soils under different TOF strata have similar quality and same SOC build up rate was observed otherwise with SPCP exhibiting highest CSQI. SPCP was observed to be more qualitative and dynamic growing system among all strata with an enhanced capacity to fix and conserve SOC to help mitigate climate change. Present study demands plantation of more trees outside the forest areas especially in the pattern of SPCP for enrichment of soil and enhancement of carbon sequestration.

Keywords: Additive soil quality index (ASQI); Kashmir Himalayas; Scattered patches with clumpy plantation (SPCP); Soil organic carbon (SOC); Trees outside forests (TOFs).