The effects of irrigation, nitrogen fertilizer and the control of pests and pathogens on spring-sown field beans (Vicia faba L.) and residual effects on two following winter wheat crops

Experiments started in 1976, 1977 and 1978 on Clay-with-Flints soil at Rothamsted tested the effects of combinations of eight two-level factors on spring-sown field beans. Factors tested, presence v. absence, were irrigation, nitrogen fertilizer, aldicarb, fonofos (dieldrin in 1976), benomyl to the seed bed, permethrin (fenitrothion in 1976), pirimicarb, benomyl foliar spray (not tested in 1976).The main pests and diseases present were nematodes of the genus Pratylenchus, the pea aphid Acyrthosiphon pisum, the pea and bean weevil Sitona lineatus, root blackening associated with the fungal genera Pythium and Fusarium, the foliar diseases chocolate spot, Botrytis spp., rust, Uromyces fabae and bean leaf roll virus.Incidence of these pests and diseases varied between years. Controlling those present increased yield by about 0·7 t grain/ha each year. The difficulty of apportioning this increase to particular pests and diseases is discussed.Irrigation increased total dry-matter production and grain yield in 1976 and 1978 but only total dry-matter production in 1977, when grain yield was lost because of lodging. Nitrogen fertilizer had little or no effect.The most favourable combinations of treatments gave yields of 3·4, 5·0 and 6·4 t grain/ha in the 3 years respectively. Small yields in 1976, despite irrigation, were attributed to premature senescence caused by exceptionally high temperatures. It is suggested that with good control of pests and diseases yields of at least 5 t/ha should be attainable on Clay-with-Flints soil without irrigation in years of average temperature and rainfall and yields in excess of 6 t/ha when the soil-moisture deficit is lessened by either above-average rainfall or irrigation.Treatments applied to the beans had little or no effect on two following crops of winter wheat.