Field measurement of net nitrogen mineralization of manured soil cropped to maize

We evaluated the in situ net nitrogen (N) mineralization in a soil cropped to maize and fertilized for 11 years with cattle slurry or farmyard manure, both common on livestock farms of the Po River valley in Northern Italy. The net N mineralization of the tilled soil layer was measured in six consecutive incubation periods after manure application, for a total of 12 weeks, using the polyethylene buried bags technique. Results showed that net N mineralization was followed by N immobilization and finally, by mineralization whose rate increase until maize flowering. On average, net N mineralization was 70.4 kg N ha(-1), with the majority being released during the last measurement period. The time and extent of net N mineralization and plant N uptakes were not affected by fresh manure application. Instead, the effect of past management increased the maximum net N mineralization rate obtained with farmyard manure. The buried bag technique probably underestimates the total amount of mineralized N available for crop growth because it excludes the presence of the plant.