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The influence of 10 years reduced tillage (RT) on the potential carbon mineralization of the 0-5 cm layer of silt loam soils in Belgium under a temperate climate was investigated. Therefore, four fields at three locations under 10 years of RT and fields under conventional tillage (CT) with comparable crop rotation were selected. The higher % soil organic carbon in the upper layer resulted in a higher potential carbon mineralization of the RT fields. The small increase in % soil organic carbon and potential carbon mineralization of RT fields was contributed to the high soil disturbance due to incorporation of manure in the upper layer and the production of sugar beets and potatoes. Simulating ploughing by emptying and refilling the soil cores resulted mostly in a higher potential carbon mineralization. However, the differences were not significant due to the high variability in potential carbon mineralization.

This paper reports on experiences with the use of the PEST (Parameter ESTimation) programme to calibrate the soil physical parameters of a nitrate leaching model (the Burns alpha model) and to determine the N mineralization rate by inverse modelling. Parameter estimation was much more efficient and accurate with the PEST programme than with a built in "trial and error" calibration module. The determination of the N mineralization rate by inverse modelling with PEST using measured nitrate concentrations was not possible, and several reasons for this are given. With more suitable experimental fields (lighter soil texture and/or deeper groundwater level), more replications in the nitrate measurements and a one-step calibration of the alpha parameter and the N mineralization rate, determination of the N mineralization rate may become possible.