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Jeffrey G. Williamson, Luis Mejia, Bradley Ferguson, Paul Miller and Dorota Z. Haman

containing ‘Emerald’ and ‘Jewel’ plants using only the ‘Emerald’ plants. The in-row plant sequence alternated between three consecutive plants of each cultivar. Twelve nonweighing, drainage lysimeters were installed during Nov. 2009 through Dec. 2009. In each

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David R. Bryla, Thomas J. Trout and James E. Ayars

is with precision weighing lysimeters, which has generally been regarded as the standard against which other measures of ET have been compared. Weighing lysimeters determine ET directly by measuring changes in mass of a soil container with plants

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Will Wheeler, Reagan Wytsalucy, Brent Black, Grant Cardon and Bruce Bugbee

drought tolerance of modern orchards, requiring less irrigation. Weighing lysimeters provide a reliable method of applying drought stress because the transpiration rate of an entire tree can be determined over short intervals, summed over a day and

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Lance V. Stott, Brent Black and Bruce Bugbee

with no leaching is due to the uptake and transpiration of water from the root zone. Weighing lysimeters, thus, provide a way to determine whole-tree transpiration rates over hours, days, and weeks ( Ben-Gal et al., 2010 ). The precision offered by

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A. Richard Renquist, Horst W. Caspari and David J. Chalmers

Nashi pear (Pyrus serotina Rehder, cv. Hosui) trees were planted in 12 computerized 1m-wide drainage lysimeters in September 1987. During the 1990 season tree water use was monitored via lysimeter and neutron probe readings. Diurnal leaf water relations were studied using a pressure chamber for water potential (ψ) and a porometer for leaf conductance (gs). Xylem sap trunk flow velocities were measured with an experimental heat pulse device and converted to xylem flux. Close agreement existed between 24 hr xylem flux and lysimeter water use when comparing trees with different soil water content. Xylem flux also was very sensitive to changes in evaporative demand. During 9–13 day drying cycles pre-dawn ψ became progressively lower, morning decline more rapid, and afternoon recovery slower. The diurnal gs pattern also shifted during drying cycles, such that gs of water stressed trees always decreased from time of first measurement of sunlit leaves rather than increasing during the morning as on non-stressed trees. Late afternoon was the best time to distinguish between fully irrigated and stressed trees using gs measurements.

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Larry E. Williams

A weighing lysimeter (with a soil container 2 m wide, 4 m long and 2 m deep) was installed at the University of California's Kearney Ag Center in 1987. Diurnal, daily and seasonal vine water use has been measured yearly since then. Vine water use was 350, 400 and 580 mm the first, second and third years after planting. respectively. Vine water use (from budbreak to October 31) the subsequent four years averaged 815 mm per year. Reference crop ET (ETo) averaged 1172 mm (from budbreak to October 31) over the course of the study. Diurnal vine water use was highly correlated with the diurnal course of solar radiation. Maximum ET averaged 50 L vine-1 day-1 during the middle part of the growing season. Experimental vines surrounding the lysimeter were irrigated at various fractions (from 0 to 140% in increments of 20%) of vine water was measured with the weighing lysimeter. Maximum yields were obtained with the 80% irrigation treatment This study demonstrated the deleterious effects of both over and under irrigation on yield of grapevines.

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Craig A. Storlie and Paul Eck

Inexpensive weighing lysimeters ($1475/unit) were constructed for measuring evapotranspiration of young highbush blueberries (Vaccinium corymbosum L.). The use of a single load cell and other design characteristics decreased lysimeter measurement accuracy but minimized lysimeter construction costs. Measurement error was within ±3%. Crop coefficient (CC) curves for 5- and 6-year-old `Bluecrop' highbush blueberry plants in their third and fourth year of production were generated using reference evapotranspiration and crop water use data from the 1991 and 1992 growing seasons. The CC increased during leaf expansion and flowering in the spring to its maximum value of about 0.19 in 1991 and 0.27 in 1992 and remained near these values until leaves began senescing in the fall. Water use on sunny days during June, July, and August ranged from (liters/bush each day) 3.5 to 4.0 in 1991 and 4.0 to 4.5 in 1992. During the second year of the study, plants had an average height of 0.9 m, an average diameter of 0.9 m, and covered 18% of the total cultivated area. The maximum calculated CC was equal to 1.5 times the measured canopy cover percentage.

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Susan L. Steinberg, Marshall J. McFarland and Josiah W. Worthington

The potential for reducing water use of peach [Prunus persica (L.) Batsch] trees with antitranspirants following fruit harvest was investigated using matched peach trees planted in an outdoor twin weighing lysimeter facility. A 10% solution of the antitranspirant Wilt Pruf NCF was applied to one of the two trees on 7 July 1986. Immediately after application, water use of the treated tree was reduced by 40%. One month after treatment, the water use was reduced 30% and, by the termination of the experiment (85 days after treatment), water use was reduced 12% as compared to control. The average reduction in tree water use for the entire period was 30%. Fully expanded, sunlit leaves (nodes 10 to 20 from the terminal end) from the treated tree exhibited the greatest reduction in water loss compared with immature or inner canopy, shaded leaves. Use of the antitranspirant did not prevent the development of water stress once a critical level of soil moisture was reached. The change in tree water use induced by the antitranspirant did not significantly reduce shoot length, new leaf production, or individual leaf size on actively growing, current-season branches. Fruit and leaf bud initiation, as measured the following spring, were not affected: however. flower bud maturation could not be evaluated due to freeze damage. Chemical name used: di-1-p-menthene (Wilt Pruf NCF).

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Aparna Gazula, Eric Simonne, Michael Dukes, George Hochmuth, Bob Hochmuth and David Studstill

Collecting leachate from lysimeters installed in the field below vegetable fields may be used to quantify the amount of nitrogen released into the environment. Because limited information exists on the optimal design type and on the effect of design components on lysimeter performance, the objective of this study were to identify existing designs and their limits, assess cost of design, and test selected designs. Ideally, lysimeters should be wide enough to collect all the water draining, long enough to reflect the plant-to-plant variability, durable enough to resist degradation, deep enough to allow for cultural practices and prevent root intrusion, have a simple design, be made of widely available materials, and be cost-effective. Also, lysimeters should not restrict gravity flow thereby resulting in a perched water table. Previous study done with a group of free-drainage lysimeters (1-m-long, 45-cm-wide, installed 45-cm-deep) under a tomato-pumpkin-rye cropping sequence resulted in variable frequency of collection and volume of leachate collected (CV of load = 170%). Improving existing design may be done by increasing the length of collection, lining the lysimeter with gravel, limiting the depth of installation, and/or breaking water tension with a fiberglass wick. Individual lysimeter cost was estimated between $56 to $84 and required 9 to 14 manhours. for construction and installation. Costs on labor may be reduced when large numbers of lysimeters are built. Labor needed for sampling 24 lysimeters was 8 man-hr/sampling date. Because load may occur after a crop, lysimeter monitoring and sampling should be done year round.

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C. D. Stanley, G. A. Clark, E. E. Albregts and F. S Zazueta

Sixteen field-located drainage lysimeters (each 60 cm wide, 2.44 m long, 60 cm deep) designed specifically for determination of water requirements for fruiting strawberry production (season - Oct to April) were installed in 1986. Each lysimeter was equipped with individual micro-irrigation and drainage collection systems automated for minimal management input. Initially, computer control (using a low-cost microcomputer) was used to continuously check switching-tensiometers located in each lysimeter and apply irrigation water as needed, A drainage suction (-10 MPa) was applied continuously to simulate field drainage conditions. Manually-installed lysimeter covers were used to protect the plots from interference from rainfall when needed, Initial irrigation application treatments were set at four levels of soil moisture tension controlled by tensiometers and were measured using flow meters for each lysimeter. This paper will discuss problems that were experienced with the initial setup (difficulty in measuring actual application amounts, tensiometer and computer control, elimination of rainfall interference, uniformity of irrigation application, and salinity in the rooting zone) and the modifications (pressurized reservoir tanks, construction of motorized rain-out shelter, micro-irrigation emitters used, and fertilization program) which have been made to overcome them,