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, a ll following winter or spring wheat, tested the effects of six differe nt 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 tr eatments on overwinter changes in soil mineral nitrogen (SMN) and plan t 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. Diff erences in net overwinter changes in SMN plus plant N between set-asid e treatments were variable and dependent on rainfall. During a wet win ter, SMN plus plant N losses were large under fallow and natural regen eration, intermediate under winter wheat and small under Italian ryegr ass (Lolium multiflorum). Ryegrass restricted the growth of the follow ing wheat but yields were unaffected where fertilizer N was applied. R yegrass proved difficult to control in the subsequent wheat test crops . Forage rape (Brassica napus) took up large amounts of N but after to pping did not compete well with weeds. Yields of the first wheat test crops after winter wheat were smaller than after the set-aside treatme nts, take-all was probably the cause of this yield depression. No cons istent yield differences were recorded in the second wheat test crops.