Effects Of Wheat-Cotton Cropping Systems On Cotton Yield Formation And Resource Use Efficiency

Wheat-cotton double cropping practiced at a large scale in the Yellow River valley and the Yangtze River valley in China, since wheat-cotton double cropping can increase multiple-crop index, and alleviate the competition for arable land between food crops and cotton. Little information was available on the productivity and resources use efficiencies of 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 (Siza 3, mid-later maturing; CCRI50, early maturing) were conducted in 2011/2012 and 2012/2013 growing seasons at the Pailou experimental station of Nanjing Agricultural University (118°50’E,32°02’N)5 Nanjing City and the cotton experimental station of Nanjing Agricultural University (33°20’N,120°46’E), Dafeng City, Jiangsu Province, China.The objectives of this study were (1) to explore the physiological mechnism of cotton yiled formation in double-cropped wheat-cotton though investaging cotton growth and development, and (2) to evalute the effects of cropping system on radiation use efficiency in double-cropped wheat-cotton via determing cotton canopy structure and the distribution of the intercepted PAR, and (3) to clarify the effects of cropping system on cotton nitrogen use nitrogen equilibrium in double-cropped wheat-cotton by examining the dynamic accumulation of nitrogen in cotton, and (4) to elucidate the effects of cropping system on soil physical and chemical properities in wheat-cotton double cropping system, and provide the valuable reference for scientific fertilization. The main results were as follows:1. Diminished source and sink capacity were the main determinants limiting lint yield in wheat-cotton double cropping systemsThe lint yield of cotton in double cropping systems was markedly lower than that of monoculture cotton. Analysis of the yield components revealed that fewer bolls per unit area, particular the upper fruit branches, was largely contributed to the reduction in cotton yield followed by the decreased boll weight. Cotton in double cropping systems showed a pronounced delay in reproductive development and reproductive growth period, which was caused by wheat shading for W/IC system, and delayed sowing for W/TC and W/DC systems. The later formation of fruits thus results in a reduction in fruit sites and boll number and also in a reduction in boll weight and pro-frost lint yield, limiting their growth and the sink capacity of the plant as a whole. The main determinant of cotton yield in W/IC and W/TC systems was the diminished source capacity, whereas the reduced sink capacity is the main determinant of cotton yield in W/DC systems. Early maturing cotton cultivar is at an advantage in wheat-cotton double cropping systems. Cropping system had significantly effect on cotton biomass and its distribution. The findings suggest that the key factor that limitied cotton yields in W/IC and W/TC systems was inadequate production of biomass, while the key determinant limiting the yield in W/DC system was the inadequate biomass and reduced partitioning to reproductive organs.2. Canopy meteorological differences affects cotton radiation use efficiency in wheat-cotton double cropping systemsThe present study indicated that the cropping systems had significant effects on the season temperature and light environment of the seedling as well the flowering and boll-formatting period of cotton. Temperature at the cotton canopy was increased, and humidity and light interception was decreased in double-cropped cotton. 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 CCRI50, while that of double cropped cotton was 1.19-1.93 g DM MJ-1 higher than monoculture cotton. The RUE of cotton was the highest in W/DC system, followed by in W/TC and W/IC systems. 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. Double cropping cotton intercepted significantly lower PAR than monoculture cotton, which is the result of the lower/PAR 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.3. Double-cropping reduced cotton nitrogen use efficiencyThe results showed that cotton N yield in double cropping systems were significantly lower than that in monoculture. Compared with MC for Siza 3, N yield of IC, TC and DC was decreased by 12.0%,20.5% and 23.4%, respectively, and 7.3%,10.7% and 17.6% for CCRI 50, respectively. The reductions of N yield in double cropping systems were largely ascribed to reduced N accumulation speed and duration of the nitrogen fast accumulation period. Double-cropped have a lower NHI as a consequence of a weaker sink caused by the delayed fruiting and boll formation in double cropping systems. Wheat-cotton double cropping systems did not use N efficiency relative to monoculture cotton. Compared with monoculture cotton, all the indices of N use efficiency (N agronomic efficiency (NAE), N apparent recovery efficiency (NRE), N physiological efficiency (NPE) and N Partial factor productivity (NPFP)) of double-cropped cotton were consistently lower, particularly for DC. Relative to mid-late maturity, early maturity cultivar of CCRI 50 took up similar quantities of N, but yielded considerably efficiency than Siza 3. The analysis of relationships between lint yield, N uptake and use efficiency showed that higher N uptake, NRE and NPFP values were favorable for enhancing cotton yield. An analysis of the crop N balance showed that conventional N-management in double cropping systems results in high N surpluses that pose an environmental risk compared to monoculture cotton. Our results suggest that the N management of cotton in double cropping systems should be improved by means of proper timing and demand-oriented dosing of N fertilization.4. Double-cropping enriched the field soil nutrientsSignificant differences were observed in the soil temperature, the contents of soil organic matter, total N, available N, P, and K under different cropping systems. On the other hand, soil bulk density was less affected by the cropping systems, indicating lager effects of cropping systems on soil chemical properties than soil physical properties. The effects were higher on soil chemical properties than on soil physical properties. The content of soil organic matter and total N increased with the growing process of cotton. There were no significant differences in soil total P content and pH value. Temporal and spatial heterogeneity of available N, P, and K contents in soil was observed in diverse cropping system cotton farm. The findings in this study with cotton-wheat double cropping system showed that soil available N, P, K in double-cropped cotton field had the similar changing trends to those in mono-cultured cotton field, but the values were significantly higher in double-cropped than in mono-cultured cotton at late growth stages of cotton, especially for DC. The main reasons for this were the straw-returning of wheat and cotton, the high rate application of nitrogen fertilizers, and the fewer uptakes of double crops.The results indicated that W/TC and W/DC should be extended in the Yangtze River Valley and that there is the potential for further enhancement in resource productivity and yield through the use of scientific agricultural practices. The early maturing cultivar appeared to be superior to the late maturing cultivar in the double cropping system. This finding has important instruct for crop management, as it suggests that there are several ways for further enhancement in double cropped cotton yield through the use of scientific agricultural practices.