Effects of N application on faba bean chocolate spot and canopy microclimate in wheat and faba bean intercropping system

A field experiment was conducted to examine the effects of nitrogen application levels, i.e. N₀ (0 kg·hm^-2), N₁ (45 kg·hm^-2), N₂ (90 kg·hm^-2), N₃ (135 kg·hm^-2), on the severity of chocolate spot and canopy microclimate in wheat and faba bean intercropping system, and to explore the relationship of canopy microclimate change and severity of chocolate spot. The results showed that the disease index of chocolate spot increased by 27.2%-58.0% in the peak infection stage, and the area under disease progress curve (AUDPC) increased by 15.0%-101.8% for both monocropped and intercropped faba bean after nitrogen application. The peak value of disease index and AUDPC appeared at N₃ (135 kg·hm^-2) level. After nitrogen application, canopy temperature decreased by 0.2-1.1 ℃ and canopy light transmittance decreased by 1.7%-29.7%, but canopy relative humidity increased by 0.5%-28.7%. Compared with monocropped faba bean, wheat and faba bean intercropped significantly decreased the chocolate spot disease index by 36.3%-48.1% and AUDPC by 44.0%-53.6%. Canopy temperature and light transmittance of intercropped faba bean increased by 2.1%-8.7% and 12.0%-53.8%, respectively. The canopy relative humidity was decreased by 11.6%-31.6%. There were significantly negative correlation between canopy temperature and light transmittance with disease index of faba bean chocolate spot. The canopy humidity was positively correlated with disease index. Our findings showed that high nitrogen application deteriorated canopy microclimate of faba bean that led to occurrence and harm of chocolate spot, and that the improvement of canopy microclimate by intercropping would be helpful for controlling faba bean chocolate spot.