Tillage-induced N mineralization and N uptake in winter wheat on a coarse sandy loam

The potential of adjusting soil N mineralization by soil tillage in the growing season was investigated in winter wheat (Triticum aestivum) on a coarse sandy loam (Typic Hapludult). In two succeeding years, wheat was sown at 25 cm row spacing on plots where four different organic matter (OM) management strategies regarding pig slurry application, straw incorporation and catch crop growing had been applied for the previous 13 years. Soil tillage was carried out in spring with a row cultivator, a PTO-driven row rotovator or a PTO-driven brushweeder. Soil inorganic N content was determined in tilled and undisturbed soil during 4 weeks after tillage. In the first experimental year, gross N transformation rates were measured by 15 N pool dilution techniques in row rotovated soil and in undisturbed soil in two of the four OM levels. The three types of soil tillage caused higher inorganic N levels in both years with an extra 7-9 mu g g(-1) soil in tilled than in undisturbed soil. The N uptake in above-ground wheat biomass harvested in spring did not respond to tillage or to increased inorganic N concentration. There was no effect of tillage on N transformation as measured by 15 N pool dilution. Higher inorganic N concentration in disturbed field soil was therefore assumed to be mainly caused by reduced crop N uptake rather than increased N mineralization. In the first year, grain yield of mature winter wheat was lower after row cultivation than after rotovation and brushweeding, but grain yield after soil tillage was not significantly different from undisturbed soil. The N uptake in grain was 4-5 kg N ha(-1) higher after rotovation and brushweeding compared to undisturbed soil. In the second year, grain yield was highest after brushweeding, whereas there was no difference in yield between two other tillage techniques and undisturbed soil. Soil tillage carried out in the second year did not influence grain N uptake. Grain N concentration was unaffected by soil tillage in both years. No interactions between tillage and OM management were observed. Thus, in regularly ploughed soil as studied here, soil tillage in the growing season does not seem to enhance N availability or improve synchronization between crop demand and N mineralization. (c) 2005 Elsevier B.V. All rights reserved.