Effects of compost input and tillage intensity on soil microbial biomass and activity under Mediterranean conditions

Soil: Use reduced tillage in arable fields

A replicated, randomized, controlled study in 2000–2009 on a farm in Sicily, Italy, found more organic matter, nitrogen, phosphorus, and soil organisms in soils with reduced tillage, compared to conventional tillage. Organic matter: More organic carbon was found in soils with reduced tillage, compared to conventional tillage (8–16 vs 6–11 g C/kg soil). Nutrients: More nitrogen or phosphorus was found in soils with reduced tillage, compared to conventional tillage, in one of two comparisons (2.2 vs 1.7 g N/kg soil; 20 vs 11 mg phosphorus/kg soil). Soil organisms: More microbial biomass (measured as carbon) was found in soils with reduced tillage, compared to conventional tillage (334–680 vs 241–464 mg C/kg soil), and more microbial biomass (measured as nitrogen) was found in one of two comparisons (102 vs 78 mg N/kg soil). Greenhouse gases: Similar amounts of carbon dioxide were found in soils with reduced tillage, compared to conventional tillage (69–71 vs 109–111 mg C-CO₂/kg soil). Methods: Conventional tillage or reduced tillage was used on eight plots each (20 x 15 m plots), in 2000–2009. A mouldboard plough (20 cm depth) was used for both conventional tillage (6–8 ploughings/year) and reduced tillage (one ploughing/year, plus hoeing to control weeds). Compost was added to all plots (15–30 t/ha/year). Soil samples were collected in May 2009 (five sub-samples/plot, 0–20 cm depth).