Effects of nitrogen application on manganese nutrition and occurrence of leaf spots of intercropped faba beans

Effects of different nitrogen application ratios (N 0, 45, 90 and 135 kg/ha) on manganese nutrition and leaf spots of faba bean in wheat and faba bean intercropping ecosystem were studied by using the field plot experiments at Yanhe town, Yuxi city, Yunnan Province during the 2005-2006 winter growing seasons. The results indicate that the faba bean yield, NH4OAc-Mn content in rhizosphere soils and manganese concentration in leaves of intercropped faba bean are significantly increased by 49.16%-87.77%, 16.27%-35.25% and 4.98%-27.75% respectively under four different nitrogen application rates compared to those in monocropping. NH4OAc-Mn content in rhizosphere soils at flowering stage and manganese concentration in leaves at branching stage are significantly increased under the nitrogen application rates (N 45, 90 and 135 kg/ha) compared to the no-N application under the intercropping system, and the optimal nitrogen fertilization rate is 90 kg/ha. The incidence and index of leaf spots of intercropped faba bean are reduced by 15.75％ and 1.5% at the maximum occurrence stage compared to those in monocropping. There are significant negative correlations between manganese concentration in leaves, and the incidence and the index of leaf spots (the correlation coefficients: -0.9399 and -0.8751 respectively). The occurrence of leaf spots are increased under higher nitrogen application (N 90 and 135 kg/ha), compared with that under lower nitrogen application (N 45 and 0 kg/ha).