Effect of cropping system on radiation use efficiency in double-cropped wheat–cotton

Wheat–cotton double cropping is the leading cropping system in the Yellow River Valley and the Yangtze River Valley in China. To comprehend the effects of cropping systems on the radiation use efficiency (RUE) in wheat–cotton double cropping, field experiments involved four cropping systems, namely monoculture cotton (MC), wheat/intercropped cotton (W/IC), wheat/transplanted cotton (W/TC) and wheat/direct-seeded cotton (W/DC) and two cotton cultivars were conducted in 2011/2012 and 2012/2013. The results showed that wheat–cotton double cropping improved radiation use by increasing the intercepted photosynthetically active radiation and RUE compared with monoculture cotton. Averaged over two years, the RUE of monoculture cotton was 1.20 g DM MJ−1 for Siza 3 and 1.14 g DM MJ−1 for CCRI 50, while that of double cropped cotton was 1.19–1.93 g DM MJ−1 higher than monoculture cotton, with the RUE of cotton in W/DC was the highest, followed by in W/TC and W/IC. The analysis of cropping systems effects on cotton canopy structure and light distribution indicated that the high RUE was associated with the favorable intra-canopy light distribution. Cotton in W/IC, W/TC and W/DC system intercepted 87.1%, 54.6% and 44.3% as much PAR as the monoculture cotton for Siza 3 and 86.9%, 59.3% and 46.2% as much PAR as the monoculture cotton for CCRI 50, respectively. Double cropping cotton intercepted significantly lower PAR than monoculture cotton, which is the result of the lower fPAR caused by initiation shading for IC, later planting for TC and delayed sowing for DC, respectively. Our results suggest that the key factor that limits cotton production in double cropping systems is their lower PAR interception rather than the RUE. Suggestions for further increasing the productivity of radiation should be based on improved capture of radiation by cotton in wheat–cotton double cropping systems. The early maturity cultivar might be more appropriate to double cropping sequential systems.