ASSESSMENT OF SOIL QUALITY AND ITS EFFECTS ON PLANT GROWTH AND SOIL FAUNA

Abstract

Soil is a vital, essentially non-renewable resource that supports the production of food and fibre, regulation of water and nutrients, storage of carbon and provides habitat for an enormous diversity of organisms. Soil quality is a composite property inferred from measurable physical, chemical and biological indicators rather than measured directly and refers to the ability of a soil to function within ecosystem and land-use boundaries.  Yet soil quality is under increasing pressure from intensive agriculture, over-fertilization, over-use of pesticides, erosion, heavy metal contamination, salinisation, compaction and climate change. Marginal degradation leads to a 10% reduction of crop yield, moderate degradation to 10–50% and severe degradation to more than 50%. Degradation in the period 1950–2010 is estimated to have reduced soil ecosystem services by 60%.  Soil quality is not directly measurable and therefore is assessed through a minimum data set of physical (structure, bulk density, porosity, water-holding capacity), chemical (pH, EC, organic carbon, N, P, K, CEC) and biological (microbial biomass, enzyme activity, faunal diversity) indicators, which are integrated into a Soil Quality Index.  Soil quality controls plant growth by controlling root penetration, water and nutrient availability and nutrient  mineralisation. Soil fauna, which represent about 23% of all described living organisms, are responsible for organic matter decomposition, nutrient cycling and soil structure formation and are sensitive bioindicators of soil condition.  Thus sustainable soil management including organic amendments, diversified cropping, conservation tillage and integrated nutrient and pest management is essential to preserving long-term soil productivity.