Chemical and biochemical indicator of manged agricultural soils

Natural events and, to a much greater extent, anthropogenic activities may have a drastic impact on soil quality. In order to maintain increasing levels of production as well as to reduce the impact of adverse effects of environmental pollution, reliable indicators of soil health are necessary. Soil enzymes activities represent the mediators of important soil functions and may provide a useful tool, along with other specific indicators, to assess soil status, its quality and productivity. Soil chemical parameters (organic carbon, total nitrogen, available phosphorus, pH, CEC, electrical conductivity, etc.) are generally related to soil fertility conditions associated with macronutrient cycles. Many of these parameters could be used as indexes to assess soil changes caused by inadequate crop management practices. The aim of this work was to measure a set of chemical and biochemical properties and their suitability as indicators of soil quality. Three soils from different intensively-farmed areas of Italy, with a high risk potential of physical, chemical and biological degradation of soil, were investigated. The three soil profiles with a long history (more than 10 years) of different treatments were as follows: a poorly drained alfisol from the alluvial Po Valley (Cremona), amended with repeated applications of pig farm sewage sludge; a volcanic soil from the piedmont area of the Sarno Valley (Palma Campania) polluted by sewage sediments from an open drain contaminated by municipal effluents; an alfisol from “Terra Rossa” soil (Bari) irrigated with saline water. Enzymatic activities, representative of biogeochemical cycles of principal nutrients, were measured too. Treated soil and control samples from Cremona generally showed similar chemical properties such as neutral pH, low level of both organic carbon and C/N ratio. Similar levels were also found for almost all enzymatic activities . Conversely, treated Naples and Bari soils differed from the corresponding control soils in several chemical parameters, reflecting significant differences in some of the enzymatic activities. For example, the higher organic carbon content in treated Naples soil resulted in a general increase of enzymatic activity levels with the exception of phosphatase, whose activity was probably depressed by the excess of phosphorus. Similarly, the higher electrical conductivity of Bari soil, caused by saline water irrigation, as well as the higher Mn and Cu contents induced a general inhibition of all enzymatic activities and the degree of inhibition varied depending on the type of enzyme.