REVERSING AGRICULTURE FROM INTENSIVE TO SUSTAINABLE IMPROVES SOIL QUALITY IN ASEMIARID SOUTH ITALIAN SOIL

Intensive agriculture (IA) is widespread in South Italy, although it requires frequent tillage, large amounts of fertilizers and irrigation water. We have assessed theefficacy of reversing IA to sustainable agriculture (SA) in recovering quality of a typical South Italy soil (Lithic Haploxeralf). This reversion, lasting from 2000 to 2007, replaced 75% of nutrients formerly supplied inorganically by farmyard manuring and reduced the tillage frequency.Several chemical and biochemical properties, functionally related to C and N mineralisation–immobilisation processesand to P and S nutrient cycles, were monitored annually from 2005 to 2007 in the spring. Reversing IA to SA decreased soil bulk density, almost doubled the soil organicmatter (SOM) as favoured the immobilisation of C and N, increased most soil microbial indicators but decreased contents of nitrate, mineral N and K2SO4-extractable C.The K2SO4-extractable C/K2SO4-extractable organic N ratio suggested that substrate quality rather than the mass of readily available C and N affected biomass and activity of soil microflora. Also, the largely higher 10-day-evolved CO2–C-to-inorganic N ratio under SA than IA indicatedthat higher C mineralisation, associated with higher microbial biomass N immobilisation, occurred under SAthan IA. Decreases in most soil enzyme activities under IA, compared to SA, were much higher than concomitant decreases in SOM content. Soil salinity and sodicity werealways higher in IA than SA soil, although not critically high, likely due to the intensive inorganic fertilisation asirrigation waters were qualitatively and quantitatively the same between the two soils. Thus, we suggest that thecumulative small but long-term saline (osmotic) and sodic(dispersing) effects in IA soil decreased the microbial variables more than total organic C and increased soil bulk density