INFLUENCE OF DIRECTION AND DISTANCE FROM TREES ON WHEAT YIELD AND PHOTOSYNTHETIC PHOTON FLUX-DENSITY (Q(P)) IN A PAULOWNIA AND WHEAT INTERCROPPING SYSTEM

A Paulownia-winter wheat intercropping experiment with the object of q uantifying photosynthetically active radiation (PAR) and its effect on wheat yield was conducted 60 km south of Zhengzhou (35 degrees N 113 degrees E), Henan Province, PR China, from September 1991 to July 1992 using a tree and crop interface approach. The middle row of three 240 m long rows of 11-year-old trees was studied for its effects on the y ield of irrigated and fertilized winter wheat. Photosynthetic photon f lux density (Q(p)) was quantified using a split-plot design with four blocks. There were four distance (subplot) treatments (2.5 m, 5 m, 10 m and 20 m) and two direction (main plot) treatments laid out to the e ast and west of a north-south tree line. Results showed no difference in direction effects but Q(p) did affect total grain weight (P = 0.004 7) between 2.5 m and 20 m. A regression equation was fit using the mea n for each distance treatment: Y = 391.7 + 4.57X with r(2) = 0.9310 in dicating a yield increase of 4.57 g m(-2) (45.7 kg ha(-1)) over a dist ance of 2.5 m to 20 m from the trees.