Research On Water Use Characteristics And Mechanism Of Alternative Irrigated Intercropping Systems

Intercropping, due to the more effective use of resources and high productivity, is practiced widely in northwestern China. In recent years, however, the shortage of water resources is increasing continually; the application of intercropping has become big challenge. Therefore, water-saving irrigation technologies for intercropping pending further study. Alternative irrigation technology can significantly improve water use efficiency of crops, creates special root system favorable for improving crop water use efficiency and helps to improve water compensate effects. Our works reported here are aiming at investigating yield, water use efficiency and water use mechanism in wheat/maize intercropping and wheat/faba-bean intercropping through field experiment and simulation experiment. The main results were obtained as the following:1. Land utilization rate, crops yield of wheat/maize intercropping were significantly increased under alternate irrigation. Land equivalent ratio (LER) of wheat/maize intercropping under alternate irrigation was varying in the range of 1.22~1.52 during 2006-2009, indicating that wheat/maize intercropping under alternate irrigation can improve land utilization rate. Apart from 2008, LER of alternative irrgated wheat/maize intercropping at medium irrigation level was increased by 2.33%~17.83% than conventional irrigation during consecutive four years. Yield of wheat/maize intercropping under alternate irrigation was increased by 51.12%~99.44% than sole wheat, and increased by 2.01%~31.74% than sole maize.2. Water consumptionn of wheat and maize was not significantly influenced by alternative irrigated wheat/maize intercropping. Compared to weighted average water consumption of sole cropping, water consumption of alternative irrigated wheat/maize intercropping was increased by 0.28%~0.92%, 4.29%~5.94%, 14.36%~19.19%, 12.72%~18.13% in 2006-2009 growing seasons, and water consumption of alternative irrigated wheat/maize intercropping was increased by 0.44%, 4.43%, 3.59%, -19.28% than wheat/maize under conventional irrigation at the same irrigation level. Water use efficiency of alternative irrigated wheat/maize intercropping was increased by 32.70%~47.10%, 31.16%~34.39%, 7.84%~20.30%, 14.42%~22.52% than weighted average sole cropping, and increased by 17.55%, 0.09%, 0.53%, 27.10% than wheat/maize intercropping under conventional irrigation at the medium irrigation level.3. The changes of water use efficiency in the alternative irrigated wheat/maize intercropping could be attributed to amount of soil evaporation propotion to evapotranspiration (E/ET), leaf area duration (LAID) and root weight density. In 2008 growing seasons, compared to sole wheat, E/ET of wheat/maize intercropping under alternate irrigation was increased by 11.71%, 9.55%, 6.00%, and increased by 5.72%, 6.19%, 6.18% than sole maize at low, medium, high irrigation level, respectively. E/ET of wheat/maize intercropping under alternate irrigation was increased by 7.17%, 4.13% than sole wheat, and 2.01%, 3.50% than sole maize at medium, low irrigation in 2009 growing seasons. LAID of alternative irrigated wheat/maize intercropping was improved by 102.78%, 105.83%, 109.14% and 60.04%, 54.49%, 54.18% than sole wheat at low, medium, high irrigation level respectively in 2007 and 2008 growing seasons. In 2009 growing season, LAID of alternative irrigated wheat/maize intercropping was improved by 76.16%,61.31% than sole wheat at medium, low irrigation level respectively.The niche differentiation in time and space of root distribution is the main mechanism for yield and water use efficiency. Root of intercropped wheat extended maize underground space in the coexistance period of wheat and maize, and root growth reached 80 cm in soil depth. Root weight density with its 0.07 root isoline reaching above 50 cm, and root isoline of 0.04 extend maize rootzone 20-40 cm.4. Increased proline content, SOD activity, POD activity and root activity were the main mechanism for improved yield and water use efficiency in alternative irrigated intercropping system. The proline content of intercropped wheat under alternate irrigation was increased by 38.3%, and sole wheat, sole faba bean averagely increased by 35.31%, 24.07% than conventional irrigation respectively. SOD activity of sole wheat, sole faba bean, intercropped wheat, intercropped faba bean under alternate irrigation was increased by 17.24%~22.62%, 21.53%~41.35%, 7.86%~25.11%, 7.92%~16.14%, POD activity was increased by 3.88%~24.53%, 0.44%~29.76%, 13.73%~35.36%, 8.79%~22.74%, and root activity was increased by 6.41%~29.98%, 5.71%~11.39%, 6.09%~22.65%, 7.62% ~20.08% than conventional irrigation during the growing period, respectively.