Effect of row space on population structure and photosynthetic available radiation in winter wheat-white clover intercropping system

Winter wheat (Triticum aestivum L.) planted with several cropping patterns were intercropped with white clover (Trifolium repens L. vs Rivendel) in 2008~2010 cultivation seasons. Population structure, photosynthetic available radiation (PAR) and yield of wheat and intercropping system were investigated. Results of the experiment with six wheat cropping patterns (3 row spaces × 2 sowing rates) indicated that total stems, LAI, biomass and yield of wheat with 25 cm and 30 cm row spaces were significantly higher than those with 40 cm row space. The yield and harvest index of wheat with 30 cm row space and 217.5 kg·hm^-2 sowing rate were 7 857.8 kg·hm^-2 and 0.483, respectively. At heading and anthesis stages, less difference was noted in PAR between 30 cm and 40 cm row space treatments at the height of 20 cm above-ground of wheat plant. PAR values above 50 μmol·m^-2·s^-1 lasted at least 8 h in the 30 cm and 40 cm row space treatments. In white clover sole cropping, however, light compensation point was in the range of 30~50 μmol·m^-2·s^-1. It suggested that winter wheat-white clover intercropping with 30 cm or 40 cm wheat row space could met the requirement of effective light for photosynthesis in white clover. Another experiment with four treatments — two wheat varieties (“Xiaoyan 81” and “Jimai 22”) as sole crops and individual intercropping with white clover at 30 cm row space — were carried out. The results showed that “Xiaoyan 81” biomass was not affected by intercropping with white clover. Its’ LAI and ear density under intercropping were higher than those under monocropping. “Jimai 22” biomass, LAI and ear density under intercropping were lower than those under monocropping. Under intercropping, diurnal PAR variation at the top of white clover canopy exhibited a unimodal curve. Diurnal PAR at bottom of white clover canopy was less than 30 μmol·m^-2·s^-1. Diurnal PAR variation at the bottom of “Xiaoyan 81”-white clover intercropping system was smaller than that in “Jimai 22”-white clover intercropping system. In general, 30 cm row space of winter wheat was the most suitable for winter wheat-white clove intercropping. With respect to wheat variety, “Xiaoyan 81” performed better than “Jimai 22” under intercropping. This study had laid the basis for developing winter wheat-white clover intercropping systems in North China Plain.