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Studies on Water Use and Water-saving Irrigation Schemes of Triploid Clones Populus Tomentosa Pulpwood Plantation

Author: LiGuangDe
Tutor: JiaLiMing;MaLvYi
School: Beijing Forestry University
Course: Forest cultivation
Keywords: hybrid triploids clones of Chinese White Popular pulpwood plantation under subsurface drip irrigation irrigation schemes water use and consumption sustainable management
CLC: S792.11
Type: PhD thesis
Year: 2010
Downloads: 81
Quote: 2
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Abstract


As the important fast-growing and high yield plantation wood species, Popular played a most important part in relieveing the contradiction between wood supply and demand, ensuring wood safety, improveing local economic, increasing farmers income, increaseing carbon dioxide absorption and carbon sequestration, and so on. But the extensive management, low productivity of Popular plantation limited the higher productive potential of Popular plantation to a large extent.In order to improve the intensive and sustainable management of clones Triploid Populus tomentosa fast-growing pulpwood means and ways of thermal dissipation sapflow monitoring technology, automatic weather station, and so on, were used in superior hybrid triploids clones of Chinese White Popular plantation in Gaotang county (36°58’N,116°14’E), Shandong province from May,2008 to November,2009. Water use characteristics and its affecting and regulating mechanism of clones Triploid P. tomentosa were mastered, water-saving irrigation equipments and methods were selected, and scientifical irrigation schedules under subsurface drip irrigation were made. And the main conclusions were introduced as below.(1) The thermal dissipation sap flow velocity probe(TDP-30) was viable to monitor clones Triploid P. tomentosa sap flow and water use with the measured error 6.79 percent. The daily variation of clones Triploid P. tomentosa sap flow velocity was of one-peak pattern whose peak and average values in sunny days were significantly higher than that in cloudy and rainy days. The sap flow velocity diurnal variation was similar at different direction east, south, west, and north. The sap flow velocity of clones Triploid P. tomentosa at four orientations was highly correlated with each other, and the regression equations of sap flow velocity at four orientations were highly significant. There was no obvious difference among the four directions Vsp in sunny and cloudy days, but in rainy day, Vsp in east was significantly higher than that in the south.There were highly significant correlated relationship between Vsp and environmental factors such as solar radiation(Qs), air temperature(Ta) and relative humidity(RH), water vapor pressure deficit(VPD), wind velocity(WS), soil water content(SWC) and temperature(Ts). Path analysis showed that Vsp of triploid P. tomentosa was mainly affected by RH and Ts in sunny day, and RH and VPD in cloudy, and rainy day. The main environmental factors regulated the Vsp daily variation were RH and VPD. (2) The average daily water use of clones Triploid P. tomentosa varied with "low-high-low" tendency from spring to summer to autumn.The water use of clones Triploid P. tomentosa were 340mm and 410mm in 2008 and 2009 respectively. The seasonal change of clones Triploid P. tomentosa water use was positively correlated with stomatal conductance(Cond), leaf area index(LAI), Qs, Ta, RH, VPD, SWC and Ts, but negatively correlated with WS. The main factors regulated seasonal change of clones Triploid P. tomentosa water use were Cond, RH, and VPD.(3) The multivariable linear regression models were made used the Vsp and main environmental factors in sunny days from April to October in 2008. The Vsp was calculated by the models and the environmental factors in 2009. There was no obvious difference between calculated values and measured value by TDP, and there relationship could be described by highly significant liner correlation. The average predicted by the models and measured value of clones Triploid P. tomentosa Vsp was 0.00161 cm·s-1 and 0.00176 cm·s-1 respectively, and the error was 8.3 percent.(4) The diurnal variation of clones Triploid P. tomentosa net photosynthetic rate(Pn) was single-peak in spring and autumn, and double-peak in summer, and the transpiration rate(Tr) was single-peak. The seasonal change of Pn was high-low-high tendency which was contrary to the Tr seasonal change. The water use efficiency(WUE) of clones Triploid P. tomentosa was higher in spring and autumn, and at early morning and nightfall in dailychange. The average Pn, Tr, and WUE of clones Triploid P. tomentosa in growth season were (6.38±1.78)μmolCO2·m-2·s-1, (3.90±0.43) mmol H2O·m-2·s-1, and (1.81±042)μmolCO2·mmol-1H2O respectively.(5) The diurnal variation of clones Triploid P. tomentosa twig and leaf absoluteness water content(AWC), relative water content(RWC), water potential(Ψ), water capacitance(C) was "V" shape. The seasonal change of twig and leaf AWC was low-high-low tendency, and the twig and leaf RWC,Ψ, and C was decreasing gradually from spring to summer to autumn. The average AWC, RWC,Ψ, C of clones Triploid P. tomentosa twig in growth season were 55.89%±1.74%, 83.36%±2.42%, (-1.51±0.24)Mpa, (0.46±0.11)g·cm-3·MPa-1 respectively and the values of leaf were 65.20%±1.64%,73.84%±4.21%, (-1.83±0.24)Mpa, (0.0049±0.0010)g·cm-3·MPa-1 respectively.The diurnal variation of clones Triploid P. tomentosa Vsp and Tr was similar, and they were highly significantly positive correlated. The relationship between Vsp and twig and leaf AWC, RWC,Ψ, C was negatively correlated. C was of more important part in regulating Vsp, especially twig water capacitance, but leaf was more important in regulating Tr than twig.(6) The best subsurface drip irrigation schemes for clones Triploid P. tomentosa pulpwood belt plantation were 50cm between two emitters, and 2 lines of laterals with 2 rows trees or 3 lines of laterals with 2 rows trees, according to the clones Triploid P. tomentosa water use efficiency, stand crown characteristics, distribution of water absorbing roots, and so on.(7) The subsurface drip irrigation system can obviously improve the stand soil and trees water conditions, increase the sap flow velocity, net photosynthetic and transpiration rate of clones Triploid P. tomentosa, and promote the trees growth, improve the paper performance of clones Triploid P. tomentosa wood. It was the best water conditions for clones Triploid P. tomentosa pulp wood plantation when the irrigation amount achieveing 70-80 percent of the soil field capacity. After subsurface drip irrigation, the stand productivity of four treatments were 11.02m3·(ha-2·a-1), 13.43m3·(ha-2·a-1),17.97m3·(ha-2·a-1), and 13.68m3·(ha-2·a-1)respectively.(8) Scientifical irrigation schedules under subsurface drip irrigation system for clones Triploid P. tomentosa pulp wood plantation in poor and enrich rainfall years were formulated respectively according to the water balance equation of planned humidity soil layer depth, ecosystem water use and consumption, effective rainfall, soil water content in growth seasons. The irrigation water requirement was 213mm(about 182 hours) and 97mm(about 83 hours) respectively in poor and enrich rainfall years. The irrigation times was 6 in poor rainfall years, one times every months from June to November, but 5 times in enrich rainfall years, one times every months in March, May and September to November.To save water and increase the irrigation water use efficiency, the best time to irrigate were before sunrise and nightfall, and the irrigation principles of "more times but fewer amount" was recommended.

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CLC: > Agricultural Sciences > Forestry > Forest tree species > Broad-leaved trees > Young
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