A comparison of management regimes for one-year rotational set-aside within a sequence of winter wheat crops, and of growing wheat without interruption. 1. Effects on soil mineral nitrogen, grain yield and quality

A series of three experiments on loam to sandy learn soil at Woburn, all following winter or spring wheat, tested the effects of six different 1-year set-aside treatments and crops of winter wheat in 1989, 1990 and 1991 on two following winter wheat test crops. !Effects of the treatments on overwinter changes in soil mineral nitrogen (SMN) and plant N in the:jet-aside years and in the first test crops were measured, as were the grain yields of both the first and second test crops. Differences in net overwinter changes in SMN plus plant N between set-aside treatments were variable and dependent on rainfall. During a wet winter, SMN plus plant N losses were large under fallow and natural regeneration, intermediate under winter wheat and small under Italian ryegrass (Lolium multiflorum). Ryegrass restricted the growth of the following wheat but yields were unaffected where fertilizer N was applied. Ryegrass proved difficult to control in the subsequent wheat test crops. Forage rape (Brassica napus) took up large amounts of N but after topping did not compete well with weeds. Yields of the first wheat test crops after winter wheat were smaller than after the set-aside treatments, take-all was probably the cause of this yield depression. No consistent yield differences were recorded in the second wheat test crops.