Abstract:

Trees and crops in an agroforestry system can make the best use of water, nutrients, irradiation and heat. However, competition may occur when the resources are scarce, especially for the water in the semi-arid warm temperate region. Water use of winter wheat ( Triticum aestivum ) in the walnut( Juglans regia )-wheat and the megranate ( Punica granatum )-wheat intercropping systems, and the wheat monoculture field was investigated at seedling establishment, jointing, flowering-filling and maturing growth period of wheat in the rocky hilly area of North China with stable carbon isotope technique. The walnut and megranate were planted in a density of 3 m between plants in the rows and 4 m between rows. The results showed that the δ ¹³C and WUE of wheat in the walnut-wheat and megranate-wheat intercropping as well as the wheat monoculture were －27.151‰, －26.788‰, －27.338‰ and 12.780, 13.285, 12.622 mmol C·mol^-1 H₂O, respectively. The two parameters were the highest in the megranate-wheat intercropping system. The average WUE of wheat in the walnut and megranate intercropping was obviously higher by 13.84% and 10.86% compared with that in the monoculture wheat at jointing period. The grain yield, total biomass and water use of the monoculture wheat were higher than that of intercropping wheat. The total water use of walnut, and megranate tree intercropping wheat were 185.92 mm and 175.27 mm, respectively, and 26.75% and 30.94% less than that of monoculture wheat (253.81 mm), suggesting that the intercropping system dramatically decreased water use of wheat. The grain yield of walnut, and megranate tree intercropping wheat was decreased 26.79% and 32.19% in comparison with monoculture wheat. There was a positive correlation between wheat grain yield and the biomass production, and both variables were positively correlated with water use, but had no obvious correlation with WUE, which reflected the more production of wheat with the more water use. In conclusion, in the 4^th year walnut and megranate-wheat intercropping systems, there was no obvious difference in fruit harvests of walnut and megranate with or without the wheat intercropping. The wheat in the intercropping system used less water, and had sound returns although the harvest was less than the monoculture wheat. Therefore it is recommended to continue the intercropping implementation in order to gain maximum economic benefit.

Key words: agroforestry, wheat, &delta, ¹³ C, WUE, water use, grain yield, biomass