Canopy light distribution and yield of winter wheat in jujube-wheat strip intercropping system

Aiming at competition for land and light between forestry and agriculture, a jujube (Ziziphus jujuba Mill.) and wheat (Triticum aestivum L.) strip intercropping system in north-south direction with 3 m × 4 m plant and row spacing was used to study light distribution of winter wheat canopy. In the field, two treatments of jujube and winter wheat intercropping (JZ) and monocrop of winter wheat (CK) were investigated during the 2013–2014 growing season. In winter wheat trip, measurement points were set at every 50 cm distance between two jujube trees (reference spacing). Thus seven measurement points were subsequently set as E50 cm, E100 cm and E150 cm, E200 cm (W200 cm) and W150 cm, W100 cm and W50 cm (E and W meant the eastern and western parts of winter wheat trip). In the monocultured winter wheat system, the same measurement pointes were set also. During different growth stages of winter wheat (tillering, jointing, heading, flowering, filling and mature stages), the photosynthetically active radiation (PAR) of winter wheat canopy in different positions was measured. At maturity, the yield of winter wheat was also investigated. The spatial windows of canopy saturated PAR of winter wheat at different growth stages were analyzed using polynomial regression and fixed interval integral so as to determine light distribution of winter wheat canopy in jujube-wheat strip intercropping system. The results showed that under strip intercropping system, canopy light intensity and yield of winter wheat had different spatial and temporal distribution characteristics. There was a certain degree of attenuation compared to winter wheat monocrop system. The space-time windows of canopy saturated PAR, grain number per spike, effective panicle number, 1000-grain weight, yield under monocrop of winter wheat (the control) were respectively 56.1%, 14.7%, 15.9%, 33.5% and 53.0% higher than those under intercropping system. Compared with monocultured winter wheat (control) the space-time windows of canopy saturated PAR of intercropped winter wheat system at E50E100 cm, E100E150 cm and E150E200 cm, and W150W200 cm, W100W150 cm and W50W100 cm suffered serious losses of 92.5%, 45.7% and 7.0%, and 5.4%, 10.9% and 54.0%, respectively. The losses of space-time windows of canopy saturated PAR resulted in a decrease in winter wheat yield, respectively, by 46.2%, 39.6% and 26.3%, 24.7%, 32.4% and 37.6%. The results of the study suggested that the differences in the degree of shading of jujube plants were the causes of the differences in yield reductions of winter wheat. The lighting quality in the west side of winter wheat strip in intercropping system was better than that in the east side during the whole growth period. As a result, jujube could be properly trimmed after winter wheat flowering and the east spacing appropriately increased, not only to control the over growth of new jujube branches, but also to improve winter wheat canopy PAR interception. This could ensure high yield of winter wheat under intercropping system of jujube and winter wheat.