Soil Quality Assessment Using Principal Component Analysis under Natural and Conventional Farming Systems in the Himalayas, India

Natural farming (NF), which leverages local ecological resources and indigenous livestock, has emerged as a potential alternative to mitigate soil degradation and ecological damage caused by intensified conventional farming (CF) under population pressure and excessive agrochemical use in the Indian Himalayas. To assess the effects of NF and CF systems on soil properties and quality, an investigation was conducted, collecting 300 soil samples (150 from each system), across six blocks in Hamirpur district, Himachal Pradesh. Samples were analysed for soil physical, chemical, and biological properties, as well as the soil quality index was computed using principal component analysis (PCA). Texturally, soils from both farming systems were classified as sandy loam to loamy sand. However, NF exhibited lower bulk density, higher porosity, and a greater maximum water-holding capacity than CF. Soil organic carbon levels were categorised as medium to high in NF, whereas they ranged from low to high in CF. Additionally, bioavailable macronutrients (N, P, K, S) and DTPA-extractable micronutrients were higher in NF. Furthermore, biological activities were generally higher in NF, except for urease activity. PCA identified five soil quality indicators for NF and six for CF, accounting for 84.7 and 89.1% of the total variance, respectively. Microbial biomass carbon, available phosphorus, sand content, and electrical conductivity emerged as novel key soil quality indicators for both systems. Overall, the NF system demonstrated higher SQI values than CF, highlighting NF’s advantages in enhancing long-term sustainability, soil fertility, and quality as well as fostering a resilient soil ecosystem.