The intercropping of wheat and fava bean is widespread in Yunnan province. Strip rust is the main wheat disease in that region. In order to assess wheat nitrogen nutrition and strip rust occurrence, two field experiments were conducted simultaneously at Yuxi and Luliang spots in Yunnan. Three nitrogen (N) fertilization rates, 0 (N0), 150 (N150) and 300 (N300) kgN ha^-1 were set for wheat as experimental treatments in three cropping patterns: wheat monoculture (Wm), wheat-fava bean intercropping (Wi) and wheat-fava bean intercropping with plastic film separation between the wheat and fava roots (Wp). Leaves nitrogen concentration (LNC) and strip rust disease index (SRDI) of wheat were surveyed during the period of disease occurrence.

The results were as follows. 1) For the three treatments, LNC under N150 and N300 treatments increased significantly compared with N0. There was no significant difference between N150 and N300. However, arranging the three treatments in different patterns, the wheat LNC markedly increased with increasing N rates (P < 0.0001). For instance, wheat LNC under N300 increased by 14.0% compared with N150. 2) For the same N rate, only under N0 at Yuxi spot, the wheat LNC of Wp and Wi increased significantly (by 52.3%) compared with Wm. There were no obvious differences between Wm, Wp and Wi under N150 or N300 at Yuxi or under any N rate at Luliang. 3) The effect of N addition on wheat strip were different between Yuxi and Luliang spots. At Yuxi, N use actually promoted wheat SRDI, and there was a clear positive correlation between wheat LNC and SRDI. However, at Luliang, wheat SRDI under N150 and N300 decreased significantly compared with N0, but there was no substantial difference between N150 and N300. The best-fit regression curve indicated that wheat SRDI first significantly decreased and then presented a rising trend with increasing wheat LNC. 4) Wheat SRDI of Wp and Wi decreased by 10.9% at the intermediate stage f the disease, but only feebly decreased at the vigorous stage compared with Wm.

The results demonstrate that under the current experimental condition, wheat-fava bean intercropping could improve wheat N nutrition only under N deficiency circumstances. Also, intercropping had a certain control effect on wheat strip rust compared with monoculture, but there were no marked effect of roots interaction between wheat and fava bean on wheat N nutrition and SRDI.