Limited short-term effect of compost and reduced tillage on N dynamics in a vegetable cropping system

Judicious management of organic matter supply and tillage practice is crucial for sustaining soil quality inhorticulture. We have studied whether N fertilization of vegetable crops should be adapted in the shortterm when soil management changes to include compost application and reduced tillage as soil qualityimproving factors. The experimental setup was a multiyear field trial on a sandy loam soil with a vegetablecrop rotation. Soil tillage in spring was either conventional (moldboard plough) or reduced, non-inversiontillage (with a specially designed chisel plough). Starting in 2008, farm compost was applied each autumnat three rates: 0, 15 and 45 Mg per hectare. The three-year crop rotation (2009–2011) consisted of broccoli (Brassica oleracea, var. Italica Group), carrots (Daucus carota) and leek (Allium porrum). Small but significant differences in N dynamics were found between treatments. Broccoli had a higher N uptakeand biomass production under reduced compared to conventional tillage. In accordance with this, the apparent net N mineralization tended to be higher for reduced tillage compared to conventional tillage. In contrast, for leek, N uptake did not differ between tillage practices despite a higher apparent net Nmineralization under conventional tillage. A tendency for a higher biomass production under conventional tillage was in line with a tendency for a higher amount of residual soil mineral N that might haveincreased the risk of N losses. In the carrot crop, a higher amount of mineral N under conventional tillagedid not increase root yield. Compost application maintained soil organic matter content and did not resultin a higher amount of residual soil mineral N. Only in the carrot growing season, compost application increased soil mineral N content to a limited extent. The small short-term changes in overall N availability observed between treatments do not necessitate changes in N fertilization strategy or additional precautions regarding residual soil mineral N.