A 3-year field experiment was conducted in 1996–98 near Penicuik, Scotland, to investigate the fate of N released after cultivation of previously long-term grass and grass-clover swards. The effects of timing of cultivations (autumn and spring), tillage methods (no tillage, ploughing to 200 mm and ploughing to 300 mm) and fertilizer N for spring (0, 40, 80 and 120 kg N/ha) and winter barley (0, 60, 120, 180 kg N/ha) on yield, N uptake and nitrate leaching were measured.
In 1996, after spring cultivation, on plots previously in grass, spring barley grain yield and N uptake did not respond to N fertilizer, but on plots previously in grass-clover there was a nearly linear response to N. In 1997, the spring barley responded to N fertilizer at all levels. Yields of 1997 winter barley after grass did not show a response above 60 kg N/ha, but increased with fertilizer N up to at least 120 kg N/ha after grass-clover. In 1998, there were strong effects of N fertilizer and cultivation method on grain yield and N uptake of both spring barley and winter barley. Winter barley grain yield was significantly higher in plots previously in grass than in plots previously in grass-clover in 1998, though not in 1997. Winter barley yields were higher than spring barley at the same fertilizer N level.
Throughout the 3 years, the no-tillage plots had consistently lower yields than the ploughed plots, but there was no consistent difference between the ploughed and deep ploughed treatments. There were strong interactive effects between tillage and previous sward in 1997. No-tillage under spring barley generally yielded lower than ploughing due to difficulties in weed control and the frequent anaerobic conditions in the soil.
Annual leaching losses were relatively small (6·4–19·6 kg N/ha). In 1996–97, more N was leached from the plots left in stubble following spring barley than from those planted with winter barley after either spring barley or grass in 1996, but in 1997–98 more N was leached from plots in winter barley than from those in over-winter stubble. Nitrate leaching was least under no-tillage, though the effect was not significant.