Effects of permanent grass versus tillage on aggregation and organic matter dynamics in a poorly developed vineyard soil

Vineyard soils are typically characterised by poor development, low organic matter content and steep slopes. Consequently, they have a limited capacity for conservation of organic matter that is weakly bound to the mineral soil phase. Under such conditions, establishment of permanent grass may improve soil quality conservation. The aim of this study was to evaluate the effects of permanent grass v. single autumn tillage on soil structure and organic matter dynamics in a hilly vineyard. During the periods 1994-1996 and 2010-2012, soil samples were collected three times per year, in different seasons. Aggregate stability analyses and organic matter fractionation were performed. The effects of grass cover on soil recovery capacity after tillage disturbance were slow to become apparent. Slight increases in aggregate resistance and organic matter contents were visible after 3 years, and the two plots (permanent grass/previously tilled) showed a large decrease of aggregate losses and increase of organic matter only after long-lasting permanent grass. However, even a single tillage produced an immediate decrease in aggregate resistance, while the organic matter content remained unaffected. Organic matter, however, showed marked seasonal dynamics, which involved not only recently added organic matter fractions but also the mineral-associated pool. Tillage altered organic matter dynamics by preventing the addition of new material into the mineral-associated organic fractions and limiting the stabilisation of aggregates.