Study On The Mechanism Of Hydraulic Lift Of The Alfalfa And Maize

Study on the Mechanism of Hydraulic Lift of the Alfalfa and MaizeThe hydraulic lift of root system and also named water reverse flow and negative transport, is a phenomenon that the roots in deep wetness soil uptake water from subsoil and carries the water through the transport tissue to the roots in topsoil and released it into the dryness topsoil around them when transpiration is low at night. However, a systematic study and report with regard to occurring mechanism of hydraulic lift is not reported up to now.In this thesis the experimental materials were alfalfa, high-yield maize zhongdan Ns2 and drought-resistant maize 8407. The experimental methods was by a installation separated the roots into the topsoil and subsoil. 503DR-neutron moisture. Soil tensiometer. BAD photosynthesis measure system and infrared ray water detector were used in the experimental. The main results acquired by the systematic determine and studies during more than two years (2000.3^2002.5) are following:l.The hydraulic lift was a kind of physical phenomenon which appearing at a certainty period and condition along with growth of plants. The average apparent quantity was lifted each night each plant in one-year life alfalfa was 8.02g, the two-year life alfalfa was 43.86g. fertility type maize Zhongdan Na2 was 7.52g and drought-tolerant maize 8407 was 4.76g. The difference of hydraulic lift was significant between different types and different categories.2. The transpiration rate of plant in experiment, the water amount of nature evaporation of soil and the water-obstructed layer of the split-root equipment in experiment has evident effect on hydraulic lift. The surface of soil was covered with plastic film lost water 5.20g by nature evaporation during one night (from 20:00 pm to following 5:00 am), the surface of soil was covered with 2 cm rough sand lost water 6.60g by nature evaporation during one night. The average lost water each hole each treatment during one night in one-year life alfalfa was 45.00g,Zhongdan N?2 maize was 6.96g and 8407maize is 5.67g.The quantity of water is lifted by hair canal through the water-obstructed layer which material was 2 cm rough sand was 6.66g, if the bottom of bucket was drilled as water obstructed layer the quantity of water was lifted by hair canal through the water-obstructed layer was 8.64g.3. In fact if the average temperature difference was 4.2 癈 during one night, average humidity difference was 6.0% and the variance range of temperature in topsoil within 8.5癈. which factors effect on the hydraulic lift of the alfalfa and maize was not obvious.4. The correlation analysis shows that intension of hydraulic lift had a positive correlation with air temperature, photosynthesis rate (Pn) and transpiration rate (TR), of the alfalfa and maize. However the correlation was negative with air humidity (RH), water use efficiency (WUE) and stoma resistance (SR) of the alfalfa and maize. Among these correlations the average transpiration rate (TR) of maize zhongdanN?2 and 8407 was distinct positive correlation with hydraulic lift of root systems, ro.05.3= 0.8916. and other of all were not significant.5. The lowest quantity of water was lifted in each treatment during one night that can be measured in one-year life alfalfa were 9.75g. and the highest was 187.68g. The lowest quantity of water was lifted in each treatment during one night that can be measured in Zhongdan N? and 8407 were 0.45g and 2.89g, respectively; the highest were 73.13g and 80.58g respectively. The highest water potential when the hydraulic lift was occurred in one-year life Alfalfa was -0.640MPa, maize 8407 was -0.502MPa and maize Zhongdan N? was -0.359MPa. The lowest water potential when the hydraulic lift was occurred of them were -1.520MPa, -1.429MPa and -1.327MPa respectively. The highest water potential difference of them were 0.914MPa, 0.825MPa and 0.671MPa respectively. The lowest water potential difference of them were 0.326MPa, 0.237MPa and 0.192MPa respectively. So, the degr...