A Study On The Fast-growing And High-yield Mechanism Of Poplar Plantations And The Irrigation System On Subsurface Drip Irrigation On Sandy Soil

The fast-growing and high-yield mechanisms of poplar plantations on subsurface drip irrigation (SDI) on sandy soil in Beijing were studied and the optimized water-saving irrigation system of SDI was also primarily researched in this paper. The results show that: The growth of poplar trees and the plantations productivity were more increased on SDI than on normal irrigation (NI). In 2000 (3 years after planted), the average Di.3, H and volume per tree are 21.18cm, 14.23m and 0.1815 m3 on SDI and were 54.5%, 36.9% and 247.6% more than on NI. The plantations productivity on SDI reached 22.78-25.81m3/ hm2.yr and were 3.9-4.6 times as long as on NI. The further study shows that: The fast-growing and high-yield mechanisms of poplar plantations on SDI were that by the soil moisture content improved sustainably, the amount of absorbing roots on SDI could be increased greatly (fine-roots (<2mm) on SDI sites increased by 88.32%), the N and K absorbed content and activated ability of trees on SDI could be increased greatly (N content of leaves, branches and coarse roots increased by 107.77-199.86%, K content of branches, fine-roots and coarse roots increased by 26.57-69.78%), the water status of trees on SDI could be continually improved (water potential of trees leaves on SDI during a day 12%-42% lower and during an irrigation period 25%-38% lower than on NI), the photosynthetic speed of individual and colony on SDI could be continually improved (the photosynthetic speed of trees leaves on SDI during a day 10.0-21.4% higher and during an irrigation period 9.0-9.9% higher than on NI), the water use efficiency of trees on SDI could be continually improved (the tiptop of increased range reached 18.5%). Based on the three treatments of 4 hours, 8 hours and 12 hours irrigation durations of SDI, the studies of the trees growth, the soil moisture, the leaves water potential, the leaves photosynthetic speedand others showed synthetically that 4 hours of SDI (the irrigated water amount was 80-120 litre/per tree . per time) was the best irrigation duration of SDI in poplar young plantations on sandy soil, the critical soil moisture of irrigation start would be between 7% and 15%, the cycle of SDI would be confirmed by it. At last, extending the underground drip irrigation in developing the fast-growing and high-yield plantations in arid, sub-arid and season arid area according to the local economic condition is suggested. And it is also suggested that a corresponding optimized water-saving irrigation system of SDI must be established on the local condition and make the plantation yields reach the high level of the world.