| Suitable land areas for food production in China remain fixed and may even be decreasing, and it is becoming more important to raise crop productivity in order to meet the increasing food requirements of an increasing population all over the world. Intercropping, through more effectively using of water, nutrients and solar energy, can significantly enhance crop productivity compared to the growth of sole crops and thus occupies an important position of agricultural production in our country and the world. A two-year experiment(in 2012 and 2013) under three N levels and three cropping systems(monocultured wheat, monocultured maize, and intercropped wheat and maize) was carried out in the Hetao Irrigation District of the Inner Mongolia Autonomous Region. The objectives of this study were to:(1) characterize the biomass, yield, growth, photosynthetic parameters, fluorescence parameters and SPAD values of both two crops;(2) explore increasing potential of wheat and maize intercropping, providing the theoretical basis for optimizing configuration of wheat and maize intercropping;(3) analyze and evaluate the resource capture and use of nutrients, light and heat, providing scientific and theoretical basis for realizing continuously high yield and high efficiency of wheat and maize intercropping. Preliminary results from this study are as follows:1, Effects of wheat and maize intercropping on growth and development of both two cropsIntercropping promoted the growth of wheat. The plant height, LAI, biomass in border wheat plants was significantly higher than in inner and monocultured wheat plants. The vegetative growth of intercropped maize was strongly depressed. The agronomic trait and LAI in intercropped maize were significantly lower than in monoculture maize. By using the expolinear model, the growth was delayed 2.39~8.24 days in intercropped maize relative to monocultured maize.Intercropping improved the dry matter allocation proportion of spike in wheat, and reduced dry matter allocating to the vegetative organs. For maize, intercropping reduced the dry matter allocation proportion of vegetative organs(stems and leafs).2, Yield and land production advantage of intercropping wheat and maizeThe grain yields were significantly higher in the intercropped wheat than in monoculture. Border effects were obvious in the intercropping but no inner effects exist. The spikelet number and kernels per spike in border plants were more than inner and monocultured wheat. The thousand seed weight in rows of intercropped wheat was lower than in monocultured wheat. The ear row number, kernels per spike, ear width in monocultured maize were higher than in intercropped maize. The kernels per row and ear length in intercropped maize were higher than monocultured maize.The LER varied from 1.01 to 1.11, indicating wheat/maize intercropping improved the land use efficiency. The LER tended to increase at higher N levels.3, Effects on nitrogen uptake and use in wheat/maize intercropping systemThe grain N content, grain N uptake, plant N uptake in intercropped wheat were higher than in monocultured wheat. The grain N content and NHI were higher in intercropped maize than in monocultured maize. During co-growth stage, the nitrogen competitive ability in wheat was stronger than in maize. And the competition intensified with N fertilization reducing. The biomass and nitrogen uptake of intercropped maize recovered under adequate nutrient; the final biomass and plant N uptake exceeded monocultured maize. Intercropping had no significant effect on nitrogen allocation proportion of various organs. Intercropping reduced the nitrogen allocation proportion of vegetative organs(stems and leafs) in maize; improving the nitrogen allocation proportion of grains.At plant level, the average IEs were 25.26~35.7 kg kg-1 for wheat; 51.94~61.66 kg kg-1 for maize. The IE of monocultured wheat was higher than that of intercropped wheat(26.42~30.12 kg kg-1), and the IE of intercropped maize was higher than that of monocultured maize(51.94~59.11 kg kg-1). At system level, the NER was higher than LER, indicating the wheat/maize intercropping used N less efficiently than the monocultures.4, Effect of wheat/maize intercropping on photosynthetic ecophysiological characteristicsAt jointing stage and filling stage, border wheat had a higher Pn and Tr relative to inner and monocultured wheat. During co-growth stage, the Pn and Tr in intercropped maize was lower than in monocultured maize. After wheat harvest, the photosynthesis of intercropped maize was recovered.Nitrogen fertilization increased the Fm, Fv, Fv/Fo of wheat, but had no significant effect on Fv/Fm at filling stage. During co-growth stage, the Fm, Fv, Fv/Fm, Fv/Fo of intercropped maize was reduced. After wheat harvest, the Fv/Fm, Fv/Fo of intercropped maize were higher than monocultured maize at N2 and N1 levels.Intercropping improved the SPAD values of wheat and lowered the SPAD values of maize.5, Effect of wheat/maize intercropping on resource capture and use of light and heatAt early co-growth stage, the solar radiation receiving in intercropped maize was reduced; the fraction of light transmitted in intercropped maize was 3.9%~6.3% lower than the monoculture maize, and the solar radiation receiving in intercropped wheat was increased. At late co-growth stage, intercropped maize gradually got rid of the stress condition of weak light; the fraction of light transmitted in intercropped maize was 19.3% higher than monoculture maize, intercropped wheat also received more solar radiation. At early co-growth stage, the soil temperature was higher in monocultured maize than in intercropped maize(2.42~2.63℃ d-1);after wheat harvest,the soil temperature was higher in intercropped maize than in monocultured maize(2.14~2.37℃ d-1).The light use efficiency of monocultured wheat reached the highest value at booting and flowering stage. The light use efficiency of monocultured maize reached the two highest values at jointing stage and middle filling stage. The light use efficiency of wheat/maize intercropping reached the two highest values at booting stage of wheat and middle filling stage of maize. For average values, the light use efficiency of intercropping(0.44~0.70%) was lower than monocultured maize but higher than monocultured wheat.The PN in the wheat/maize intercropping system was higher than monocultured wheat and monocultured maize, indicating wheat/maize intercropping had higher heat resource utilization efficiency.6, The feasibility and mechanism of improving the potential of wheat/maize intercropping systemBased on the results above, wheat/maize intercropping had higher land use efficiency. However, it had no advantage in improving nitrogen use efficiency; wheat/maize intercropping reduced the nitrogen use efficiency as a whole. Hence, improving the nitrogen use efficiency of wheat/maize intercropping system further is still challenging.Wheat/maize intercropping can improve light use efficiency and heat use efficiency. However, temporal and spatial distribution of light and heat had a markedly different effect on wheat and maize: intercropped wheat obtained more light and heat, promoting the growth; intercropped maize performed a recovery effect after wheat harvest, even so, due to less heat and light for a long time during co-growth stage, intercropped maize still performed suppressed status, delaying growth and development.Therefore, during co-growth stage, cultivating the high photosynthetic efficiency maize varieties and covers of plastic film or planting on ridges may increase the potential of this intercropping system. |
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