| Compared with monoculture, the main advantage of intercropping is improving grain yield on a given piece of land by making more efficient use of the available agricultural resources such as radiation, water, and nitrogen. In recent years, natural resources, such as arable land and water, are becoming more and more limited with quick social development and rapid growth of industry and population, which constitutes a serious threat on food supply security in China. Study on light and water use machinisms in intercropping systems can help to popularize and guide the intercropping practice, saving agricultural wter use and ensure food supply security.In this study, a three- year(2012-2014) field experiment was conducted at Shahaoqu experimental station in Hetao irrigation district in Inner Mongolia, to investigate the radiation transmission, radiation use efficiency, evapotranspiration, water use efficiency, soil water dynamics and root distribution in wheat/maize strip intercropping system. The main results are as following:(1) A semi-empirical model was developed to estimate radiation interception by strip intercrops. Taking into account the heterogeneity of leaf distribution in both horizontal and vertical direction in intercropped canopy, a semi-empirical model(Extended row crop radiation transmission model, ERCRT model) was developed to estimate radiation interception by strip intercrops based on radiation transmission theory for row crop. Measured photosynthetic active radiation(PAR) interception in wheat/maize intercropping system was used to validate the model. Compared with traditional radiation transmission model for intercropping, the ERCRT model is more powerful when the intercropping strip is relatively wide, or/and the plant density in intercropping is relatively low. The ERCRT model not only can be used to estimate the radiation interception, it also can be applied to partition radiation among different crops and soil. The inputs of the ERCRT model is very simple, only incident radiation, leaf area index and data concering canopy structure are needed. The model may also be applicable in other intercrops where the canopy of each crops could be assumed to be strip shaped. Based on the ERCRT model, it was found that 6 rows of wheat(row distance 15 cm) intercropped with 2 rows of maize(row distance 40 cm) was the best planting pattern from the perspective of radiation interception.(2) PAR interception and use efficiency of intercropped canopy was analysed. The amount of PAR intercepted by I62(6 rows of wheat intercropped with 2 rows of maize) intercepted 1034.3, 912.9, and 1051.6 MJ m-2,respectively, in 2012, 2013, and 2014, which were 4%, 5%, and 4% larger than I124, 38%, 26%, and 29% higher than sole wheat, and 13%, 15%, and 11% higher than sole maize. The radiation caption ratio of intercropping relative to sole crops was larger than 1.0 through out the whole growing season, which was the largest during later season after the harvest of wheat while the least during wheat/maize co-growth. In 2012, I62 and I124 captured 25% and 20% more radiation, respectively, than sole crops. In 2013, the values were 20% and 15%. The values in 2014 was almost the same as that in 2013. The averaged radiation use efficiency(RUE) values were 3.08 and 3.15 g MJ-1 for maize in I62 and I124, respectively, which were 10% and 8% lower than that for sole maize(3.43 g MJ-1). No significant difference was found between the RUE of intercropped wheat and sole wheat. For wheat, the net photosynthesis rate(Pn) and stomatal conductance(Gs) of the third leaf in intercropped border row were significantly higher than those in intercropped inner row and sole crops, the quantum yield of photosynthesis system II(ΦPSII) and electron transport rate(ETR) of leaves in border row were also significantly higher than those in inner row and sole crops. For maize, the Pn, Gs, ΦPSII and ETR of leaves in superstratum had no significant differences between intercropping and sole cropping, while those values for leaves in substratum was much lower in sole plots than in intercropping plots. These results indicating that photosynthesis potential of wheat and maize leaves in substratum could be enhanced by intercropping.(3) Soil evaporation and evapotranspiration of wheat/maize intercropping system were analysed and the Shuttle-Wallace model were validated. When full irrigated, wheat/maize intercropping consumed larger amount of water than sole cropping systems, while the sole wheat consumed the least. The ratio of soil evaporation to evapotranspiration was almost 0.4 in wheat/maize strip intercropping, which was less than 0.25 for sole plots. The changes in water use of wheat/maize strip intercropping relative to sole crops(ΔWU) varied between 0.24 and 0.26, and the changes in water use efficiency(ΔWUE) were nearly zero, which means that the water consumption of wheat/maize intercropping was far more than sole crops while the water use efficiency of wheat/maize intercropping was as the same as sole crops. The Shuttle-Wallace dual source model and extended multi-source model were applied to simulate evapotranspiration in wheat/maize strip intercropping system.Results showed that applying dual-source model in wheat/maize strip intercropping will cause overestimation of evapotranspiration. The simulating results was reliable when calculating evapotranspiration of wheat and maize strips separately using the Shuttle-Wallace model. The Shuttle-Wallace model could be used to analyse evapotranspiration partitioning in wheat/maize intercropping system.(4) Effects of water limitation on yield and water use of wheat/maize intercropping system were tested with field experiment. The interspecific competition in wheat/maize intercropping was intensified by water stress. For water limitation applied during the wheat booting/maize V5 stage(2012), the yield advantage of intercropped wheat(IW) over sole wheat was enhanced, whereas that of intercropped maize(IM) over sole maize was reduced compared with full irrigated treatments; for water limitation applied during the wheat grain filling/maize V9 stage(2014), the yield advantage of IW slightly improved, whereas that of IM was also reduced; for water limitation applied during the wheat jointing/maize V2 stage(2013), the yield advantages of both IW and IM were greatly reduced. The total yield of wheat/maize intercropping was 13.3, 11.4, and 14.8 t ha-1 in 2012, 2013, and 2014, respectively, which was reduced by 8%, 28%, and 15% by water limitation. The yield advantage of intercropping under limited irrigation was 25%, 3%, and 18% in 2012, 2013 and 2014, respectively, whereas that under full irrigation ranged between 22-24% over the three seasons. Root system of intercropped wheat extended to the center of maize strip while that of intercropped maize only extended to the position under wheat border row. Water limitation during wheat heading and filling stages would accelerate the compensation in water use between intercropped wheat and maize. After the application of water limitation, the ΔWU of intercropping was reduced to 18-24%; the ΔWUE of intercropping stayed at nearly zero in 2012 and 2014 but decreased to a value of-13% in 2013. |
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