Strong effect of compost and reduced tillage on C dynamics but not on N dynamics in a vegetable cropping system

Organic matter supply by compost and the way it is incorporated are important issues for sustaining soil quality in horticulture. Our research question was how compost application and reduced tillage would affect soil N dynamics and fertilizer N availability. To this end a multiyear field trial on a sandy loam soil with a vegetable crop rotation was set up. Soil tillage in spring was executed either with a moldboard plough or with an Actisol cultivator designed for non-inversion soil tillage. Farm compost was applied each autumn, starting in 2008, at 3 different rates, i.e. 0, 15 and 45 Mg per hectare. In 2011 leek (Allium porrum) was cultivated as test crop. Top mineral N dressing (0, 30 or 60 kg N ha-1) eight weeks after planting was added as a third factor. After three years significant differences between treatments were observed with respect to pH, total organic C and hot water extractable C content in the 0-10 cm soil layer. Only a few significant differences in N dynamics between treatments were registered. Residual N at the end of the growing season only varied due to differences in top mineral N dressing. The resulting higher C stocks did not appear to affect the risk of nitrate leaching.