Response of wheat yield to light distribution in intercropped Paulownia fortuneii shelterbelt and wheat

Paulownia fortuneii-wheat intercropping system is one of the most important agro-forestry ecosystems in Yellow-Huai-Hai River Flooding Plain in China. In this paper, a P. fortuneii shelterbelt intercropped with wheat was studied in order to determine light distribution and its impact on wheat yield. A total of 24 observation points with different differences to P. fortuneii shelterbelt were set to monitor photosynthetically active radiation (PAR) and 72 quadrats investigated to measure wheat yield, 1000-grain weight and grains per unit area for the period 2013-2015. Correlations between PAR at 3 key stages (including flowering stage, grain-filling stage and whole growth stage) and wheat yield, 1000-grain weight and grains per unit area were then analyzed. The results suggested that PAR and transmittance increased along with increasing distance from Paulownia shelterbelt and there were significant changes within 10 m (approximately 1-fold tree stem height) in the Paulownia shelterbelt. PAR and transmittance changed slightly above the distance of 10 m apart. The transmittance at 2 m apart from the south of the shelterbelt at grain-filling stage was smallest among all the observation points at 3 growth stages. The correlations were significant between wheat yield and PAR for whole growth period (r=0.918, P=0.000), the number of grains and PAR at flowering stage (r=0.926, P=0.000), the 1000-grain weight and PAR at grain-filling stage (r=0.922, P=0.000). The number of grains per unit area and 1000-grain weight were directly affected by shelterbelt overshadow both at flowering stage and grain-filling stage. The spatial difference in wheat yield in the intercropping system was explained by the difference in number of grains per unit area. The linear regression equation for wheat yield (y) and PAR (x) was y=0.121 3 x+95.117 (R²=0.842). The K-W rank test (P=0.609) at equation precision of 91.8% showed no significant difference between predicted yield and actual yield. The equation (in combination with observed PAR) was suitable for predicting wheat yield in the intercropping system. This study provided theoretical basis for establishing predictive model of ecosystem productivity and for designing optimal structure of Paulownia-wheat intercropping system.