Heat Balance Stem Flow Gauges Research Articles

Performance assessment of the AquaCrop model for film-mulched maize with full drip irrigation in Northwest China

Research on field water consumption is critical for optimizing crop growth and policy-making, in which the computer models play an increasingly important role. As a water-driven crop model, the AquaCrop model has been used in a large number of studies since its launch in 2009. However, how the model performs in predicting the ecohydrological process of farmland under film-mulched drip irrigation is still unclear, especially its application on partitioning crop evapotranspiration is very rarely reported. To make up for the above insufficiency, maize experiments were conducted under full mulch drip irrigation with observation instruments of eddy covariance systems, heat balance stem-flow gauges, micro-lysimeters and other tools, during seasons of 2014–2018. The AquaCrop model was first calibrated using measured data in 2014, and subsequently validated with data in 2015–2018. Results indicate that the parameterized model could precisely simulate the canopy cover ( $${R}^{2}$$ = 0.97), biomass ( $${R}^{2}$$ = 0.99) and grain yield (standard deviation was 4.13%), as well as reflect the patterns of daily variation in transpiration and evapotranspiration with satisfactory $${R}^{2}$$ of 0.91 and 0.87, respectively. Nevertheless, the $${R}^{2}$$ values of soil water content and evaporation were not good, ranging between 0.23 and 0.45, and 0.26 and 0.75, respectively. The AquaCrop model adopts canopy cover instead of leaf area index to describe the growing process of crops; this is an important innovation for model extension and application but also may lead to some inaccuracies in water balance simulation. Summarizing, this study shows that the AquaCrop model is appropriate for supporting crop production but not for predicting the soil moisture content and evaporation variation for maize under film-mulching drip irrigation.

Relations among Sap Flow, Soil Moisture, Weather, and Soybean Plant Parameters in High Water Demand and Final Growth Stages

The dynamics of sap flow in relation to plant morphology and weather conditions during reproductive growth of soybean (Glycine max. L. Merr.) influence decisions pertaining to efficient irrigation management and other inputs for high yields. Field studies began in 2017 at Marianna, Arkansas to measure moisture dynamics of soybeans during seed fill (R5 to R7) using heat balance stem flow gauges. Sap flow was highly correlated to solar radiation with maximum rates observed during beginning seed fill (R5). A solar radiation efficiency (SRE) value, calculated as hourly sap flow rate per Watt-hour of solar radiation (g/Wh2), is proposed. The SRE relates to crop water demand and hydraulic resistance of the soil-root-stem-leaf-pod-seed pathway. SRE values ranged from 0 - 1.2 g/Wh2. Soil moisture, growth stage, time of day, and weather conditions influenced the SRE, with higher values observed in the morning, late afternoon, and during R5 growth. Peak sap flows of 39 g/h at R5, 25 g/h at R6, and 3 g/h at R7 occurred. The ratio of measured sap flow to estimated crop evapotranspiration was 0.9 to 1.3 during R5 to R6.9 (maximum dry matter), but dropped to 0.2 at R7. Further research is needed to better understand late season reproductive moisture dynamics in soybeans.

Determination of the water use and water use response of canola to solar radiation and temperature by using heat balance stem flow gauges

Sap flow gauges using a heat balance have been reliable for measuring real-time transpiration in a number of crops. However, information on the accuracy of sap flow gauges in canola is lacking. Therefore, a study was conducted to validate the sap flow system in canola and to observe sap flow response to variations in temperature and solar radiation. There were strong relationships between sap flow measured with sap flow gauges and actual transpiration measured by the gravimetric method over short periods of 1 h (r2 = 0.93 and RMSE = 2.34 g h-1), and over longer periods of 1 d (r2 = 0.83 and RMSE = 48 g d-1), although sap flow slightly overestimated transpiration. In both cases the slope was not significantly different from 1. Water use in canola, estimated with sap flow gauges or from actual transpiration measurement, was dependent upon temperature (r2 = 0.94 to 0.96). Water use increased until daytime temperatures reached 36°C, after which water use decreased. Sap flow followed solar radiation trends in the field. Heat is lost or dissipated from the gauges convectively as the sap flows through the stem, conductively through the solid stem material, and radially into the surrounding air. As the convective proportion of the heat loss from the gauge increased, the accuracy of the water use estimation using the sap flow gauges increased. For sunny days, convective heat loss through sap flow accounted for a major portion of the total heat input to the gauges, while on cloudy days radial heat loss from the gauges accounted for a major portion of the heat input. Thus, at low sap flow rates during cloudy days, the possibility of error in the sap flow system was high. Overall, sap flow in canola was strongly related to daily solar radiation (r2 = 0.92). The sensitive response to weather variations and the possibility of improving the accuracy at high flow rates in the field makes the use of sap flow gauges a viable option for measuring real-time transpiration in canola. Key words: Brassica napus, canola, heat balance, sap flow, transpiration, temperature, solar radiation

Water use patterns of eastern black nightshade (Solanum ptycanthum) and hairy nightshade (Solanum sarrachoides) in response to shading and water stress

Greenhouse and growth room experiments were conducted to determine the effects of shading and water stress on transpiration of eastern black nightshade (Solanum ptycanthum) and hairy nightshade (S. sarrachoides). Transpiration rates were estimated using heat balance stem flow gauges. Eastern black nightshade transpired significantly more water than hairy nightshade given ample water and light. Eastern black nightshade also transpired more water than hairy nightshade when shaded. Transpiration of both species increased with light intensity and was relatively insensitive to changes in soil volumetric water content above 0.10 m3 m−3, but declined sharply below that level. Eastern black nightshade had significantly more stomata than hairy nightshade, particularly on the lower leaf surface. Key words: Sap flow, stomata

Effects of heat balance stem-flow gauges and associated silicone compound on ash trees

Stem-flow gauges were used to estimate water use by young ash trees ( Fraxinus excelsior L.) growing in the field at the University of Nottingham, Sutton Bonington Campus, Loughborough. In 1992 and 1993 the trees were exposed to episodes of elevated ozone concentration or to clean air in open-top chambers. Trunk constriction was observed on trees fitted with gauges in 1992, resulting in impaired flushing and growth in the spring of 1993. Despite precautions, constriction was again observed in 1993. Also in 1993 an experiment was conducted to assess the effect on ash trees of the silicone compound used with gauges to enhance performance and aid fitting to the trunks. Trunk constriction was observed when the compound was applied to the trunks without the use of gauges or any other physical restriction to radial growth. Data which demonstrate the degree of constriction are presented.

Determination of the water use of two pairs of soybean isolines differing in stomatal frequency using a heat balance stem flow gauge

Using heat-balance stem flow gauges, we were able to measure directly and continuously the sap flow rates in two pairs of soybean [Glycine max (L.) Merr.] isolines differing in stomatal frequency. Plants with high stomatal frequency transpired significantly more water than the low stomatal frequency plants at high soil moisture levels. Under low soil moisture levels, the water use rate decreased greatly for the high stomatal frequency plants. Plants with low stomatal frequency were able to maintain greater sap flow rates than those with high stomatal frequency. Higher leaf temperatures associated with the low stomatal frequency plants were likely due to lower transpiration rates which reduced evaporative cooling especially under well-watered conditions. Key words:Glycine max (L.) Merr., transpiration, water deficits

Water use by Geraldton wax (Chamelaucium uncinatumSchauer) as measured by heat balance stem flow gauges

Abstract Calibrated heat balance stem flow gauges were used to study the daily water use by Geraldton wax (Chamelaucium uncinatum Schauer), a plant endemic to the coastal sand plains north of Perth, Western Australia. Sap flow was recorded for the trunk, primary and secondary branches, and partially shaded lower east and sun‐lit upper west branches in order to assess the influence of climatic variables, stem development, and exposure. Irradiance and leaf area strongly influenced diurnal sap flow. Sap flow in primary and secondary branches was comparable when expressed on a unit leaf area basis. Defoliation reduced water use of the secondary branch. Shedding of leaves under water stress, a common phenomenon in Geraldton wax, probably has similar effects. The level of internal shading influenced water use in the crown (1.2 and 1.5 kg/day per m2 leaf area for branches with east and west exposure respectively). The difference in water use was prominent during the afternoon when the east branch was shaded. The results demonstrate the value of the heat balance stem flow gauges in measuring shrub water use directly.

826 PB 301 WATER USE OF LANDSCAPE SHRUBS SURROUNDED BY 4 DIFFERENT MULCHES

A study was conducted to explore how different mulches affect water use of landscape plants. Plots 4.9 m × 7.3 m, were covered with 5cm pine bark, cypress, white rock, or clay aggregate. 3 potted plants of Ligustrum japonicum (wax-leaf ligustrum) and Photinia × fraseri (red tip photinia) were placed in each plot so that the top of each pot was at ground level. 1 plant of each species was planted directly into each plot. Water loss was measured on a daily basis, both gravimetrically and using heat balance stem flow gauges, during both the 1992 and 1993 growing seasons. Stomatal conductance was measured periodically during each growing season. Surface, air, and soil temperatures at two depths were recorded. During 1992, pine bark mulched plants consistently used more water than the other treatments, as opposed to summer 1993 when the most water was used by plants over white rock. Surface temperatures of pine bark, cypress and clay aggregates were higher than those of white rock both years, by as much as 20C, while temperatures under the mulch varied as much as 5C between pine bark and white rock.

Stem flow and porometer measurements of transpiration from honey mesquite (Prosopis glandulosa)

The objective of this study was to compare stem flow and porometer methods of measuring transpiration of honey mesquite (Prosopis glandulosa) trees on a semiarid site. Stem flow was measured using heat balance stem flow gauges. Porometer measurements of leaf stomatal conductance (g s ) were made within foliage layers of each stem and scaled to transpiration values for the entire stem (E stem ) using stem leaf area. Simultaneous measurements using both methods were made diurnally and under artificially imposed stem shading or defoliation in June and October 1990. Stem flow and E stem had similar diurnal patterns except on 2 d in June when E stem increased during the afternoon while stem flow declined relative to midday values

Interaction of Cotton (Gossypium hirsutum) and Velvetleaf (Abutilon theophrasti) Plants for Water is Affected by Their Interaction for Light

Transpirations of cotton and velvetleaf plants competing for water and light were estimated with heat balance stem flow gauges in a controlled environment. Cotton and velvetleaf plants were grown together in pots and monitored during fluctuations in soil water, irradiance, air temperature, and humidity. Shading from other plants imposed light competition on velvetleaf or cotton. Velvetleaf used significantly more water than cotton given ample water and light. Transpiration by both species was reduced in dry soil, but velvetleaf transpiration was reduced primarily by leaf abscision, while cotton leaves did not abscise. Both cotton and velvetleaf plants transpired significantly less when shaded. Leaf water potentials indicated that shaded plants experienced reduced evaporative demand suggesting that shading reduced plant stress in dry soil. Competition for water was strongly influenced by competition for light.

Transpiration by Crape Myrtle Cultivars Surrounded by Mulch, Soil, and Turfgrass Surfaces

A study was conducted to explore how surface materials, including pine bark mulch, bare soil, and turfgrass, affect water use of diverse cultivars (dwarf weeping, dwarf upright, standard weeping, and standard upright) of crape myrtle (Lagerstroemia indica L.). Daily water use was measured gravimetrically, and instantaneous rates of sap flow were measured using heat balance stem flow gauges. Plants of all cultivars surrounded by the mulched surface lost 0.63 to 1.25 kg·m-2·day-1 more water than plants on the soil surface and 0.83 to 1.09 kg·m-2·day-1 more than plants surrounded by turf. The surface temperature of the mulch was higher than that of the other surfaces, resulting in greater fluxes of longwave radiation from the surface. Because of the greater energy load, plants on the mulched surface had higher leaf temperatures and higher leaf-air vapor pressure deficits (VPD) throughout the day. Plants on the mulched area also had higher stomata1 conductances during most of the day compared with those on bare soil and turfgrass surfaces.

Dynamics of a Heat Balance Stem Flow Gauge during High Flow

AbstractThe heat balance technique shows promise as a method for determining mass flow of sap in stems of intact plants. Previous work has been limited to plants with stems diameters near 10 mm transpiring at low rates. We evaluated the performance of several heat balance stem flow gauges during periods of high transpiration in sunflower (Helianthus annuus L.) with stems approximately 16 mm in diameter. Measurements in a controlled environment were used to compare gauge measurements to gravimetric estimates of transpiration. Gauges having heater widths of 10 mm severely overestimated flow as transpiration approached 200 g/h. Dynamics of the heat balance and temperature profiles suggested that failure of the gauge was due to a lack of thermal equilibrium between the xylem fluid and sensors on the stem surface. Increasing the heat applied to the stem did not improve gauge performance. A gauge with a heater width of 20 mm was constructed and evaluated under similar conditions. Increasing the heater width greatly improved gauge performance and the sensitivity of the measurement during high flow. Additionally, the gauge had the ability to react to large changes in flow over short time intervals. The gauge with the wide heater measured cumulative water loss over a 15‐h period to within 5% of that determined gravimetrically. The study indicates that the relationship between stem diameter and heater width is a crucial component of gauge design, and should be rigorously evaluated when applying the technique to stems with previously untested characteristics. Results suggest that heater width should be enlarged as stem diameter increases.