Estimating water fluxes in Douglas-fir plantations

1985 ◽  
Vol 15 (4) ◽  
pp. 701-707 ◽  
Author(s):  
Susan J. Riha ◽  
Gaylon S. Campbell
Keyword(s):  
Soil Water ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Field Measurements ◽  
Douglas Fir ◽  
Root Uptake ◽  
Richards Equation ◽  
Water Fluxes ◽  
Air Temperatures ◽  
Dimensional Finite Element

A model was developed to estimate water fluxes in Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) plantations using daily measurements of precipitation and maximum and minimum air temperatures. Soil water flow was modeled using a one-dimensional finite element solution to the Richards equation, with precipitation and root uptake of water included as source and sink terms. Soil hydraulic properties varied as a function of depth. Root uptake of water was based on an analog water uptake model modified to include root resistance and cylindrical flow of water. Potential evapotranspiration was calculated assuming leaf and air temperature did not differ and assuming stomatal conductance was dependent on the vapor density deficit of the air. Model validity was tested by comparing predictions with field measurements of soil water content made in the summer of 1978 at two locations in western Washington. In general, the model predicted the observed drying of the soil. Aspects of the simulated water budget for these Douglas-fir stands considered most significant were (i) the use of soil-stored water for transpiration in the summer, (ii) the net flux of water into the root zone from deeper in the soil during the summer, (iii) the dependence of water reaching the soil in the summer on the intensity of rainfall, (iv) the large percentage of the total transpiration that occurred in spring and fall, and (v) the large amount of water moving out of the soil profile in the winter.

scholarly journals A MODEL FOR ESTIMATING ACTUAL EVAPOTRANSPIRATION FROM POTENTIAL EVAPOTRANSPIRATION

1975 ◽  
Vol 6 (3) ◽  
pp. 170-188 ◽  
Author(s):  
K. J. KRISTENSEN ◽  
S. E. JENSEN
Keyword(s):  
Water Content ◽  
Soil Water ◽  
Soil Water Content ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Actual Evapotranspiration ◽  
Vegetation Density ◽  
Rainfall Distribution ◽  
Sugar Beets

A model for calculating the daily actual evapotranspiration based on the potential one is presented. The potential evapotranspiration is reduced according to vegetation density, water content in the root zone, and the rainfall distribution. The model is tested by comparing measured (EAm) and calculated (EAc) evapotranspirations from barley, fodder sugar beets, and grass over a four year period. The measured and calculated values agree within 10 %. The model also yields information on soil water content and runoff from the root zone.

Water balance and irrigation planning in a forest tree nursery

1989 ◽  
Vol 19 (5) ◽  
pp. 575-579
Author(s):  
Marcel Prévost ◽  
Jean Stein ◽  
André P. Plamondon
Keyword(s):  
Soil Water ◽  
Water Loss ◽  
Soil Profile ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Forest Tree ◽  
Irrigation Planning ◽  
Tree Nursery ◽  
Soil Water Tension ◽  
Water Tension

A soil water budget was established to estimate the water loss from the 0- to 60-cm layer as a result of evapotranspiration in a forest tree nursery. Estimated evapotranspiration totaled 69% of potential evapotranspiration (as estimated by the Penman equation) for 36 selected periods from May 15 to July 30, 1975. The root zone (0- to 15-cm layer) supplied 58% of the total evapotranspired water from the soil profile. Evapotranspiration from this layer was found to be a good predictor of total water loss. Evapotranspiration from the root zone, expressed as a percentage of potential evapotranspiration, was related to soil water tension at 3 cm depth. This relationship, combined with a knowledge of soil hydrodynamic properties, can be used to estimate evapotranspiration from the 0- to 60-cm soil profile, which in turn can be used to predict irrigation needs. For practical purposes, a relationship using net radiation instead of potential evapotranspiration can also be used. Depending on the available information, either of these two relationships may be used for irrigation planning.

scholarly journals Using StorAge Selection functions to quantify ecohydrological controls on the time-variant age of evapotranspiration, soil water, and recharge

2018 ◽  
Author(s):  
Aaron A. Smith ◽  
Doerthe Tetzlaff ◽  
Chris Soulsby
Keyword(s):  
Soil Moisture ◽  
Surface Water ◽  
Soil Water ◽  
Water Uptake ◽  
Root Water Uptake ◽  
Soil Evaporation ◽  
Root Uptake ◽  
Water Fluxes ◽  
Near Surface ◽  
Moisture Conditions

Abstract. Quantifying ecohydrological controls on soil water availability is essential to understand temporal variations in catchment storage. Soil water is subject to numerous time-variable fluxes (evaporation, root-uptake, and recharge), each with different water ages which in turn affect the age of water in storage. Here, we adapt StorAge Selection (SAS) function theory to investigate water flow in soils and identify soil evaporation and root-water uptake sources from depth. We use this to quantify the effects of soil-vegetation interactions on the inter-relationships between water fluxes, storage, and age. The novel modification of the SAS function framework is tested against empirical data from two contrasting soil-vegetation units in the Scottish Highlands; these are characterised by significant preferential flow, transporting younger water through the soil during high soil moisture conditions. Dominant young water fluxes, along with relatively low rainfall intensities, explain relatively stable soil water ages through time and with depth. Soil evaporation sources were more time-invariant with high preference for near-surface water, independent of soil moisture conditions, and resulting in soil evaporation water ages similar to near-surface soil waters (mean age: 50–65 days). Sources of root-water uptake were more variable: preferential near-surface water uptake occurred in wet conditions, with a deeper root-uptake source during dry soil conditions, which resulted in more variable water ages of transpiration (mean age: 56–79 days). The simple model structure provides a parsimonious means of constraining the water age of multiple fluxes from the upper part of the critical zone during time-varying conditions improving our understanding of vegetation influences on catchment scale water fluxes.

scholarly journals Nitrate leaching through climatologic water balance in a fertigated coffee plantation

Revista CERES ◽  
2013 ◽  
Vol 60 (6) ◽  
pp. 785-792 ◽  
Author(s):  
Rafael Pivotto Bortolotto ◽  
Isabeli Pereira Bruno ◽  
Durval Dourado-Neto ◽  
Luís Carlos Timm ◽  
Adilson Nunes da Silva ◽  
...  
Keyword(s):  
Water Balance ◽  
Soil Solution ◽  
Nitrate Leaching ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Cost Benefit ◽  
Water Fluxes ◽  
Rainfall Events ◽  
Nitrate Losses ◽  
Nitrogen Rates

Nitrate losses from soil profiles by leaching should preferentially be monitored during high rainfall events and during irrigation when fertilizer nitrogen applications are elevated. Using a climatologic water balance, based on the models of Thornthwaite and Penman Monteith for potential evapotranspiration, drainage soil water fluxes below the root zone were estimated in a fertigated coffee crop. Soil solution extraction at the depth of 1 m allowed the calculation of nitrate leaching. The average nitrate concentration in soil solution for plots that received nitrogen by fertigation at a rate of 400 kg ha-1, was 5.42 mg L-1, surpassing the limit of the Brazilian legislation of 10.0 mg L-1, only during one month. For plots receiving 800 kg ha-1 of nitrogen, the average was 25.01 mg L-1, 2.5 times higher than the above-mentioned limit. This information indicates that nitrogen rates higher than 400 kg ha-1 are potentially polluting the ground water. Yearly nitrate amounts of leaching were 24.2 and 153.0 kg ha-1 for the nitrogen rates of 400 and 800 kg ha-1, respectively. The six times higher loss indicates a cost/benefit problem for coffee fertigations above 400 kg ha-1.

Modeling Evapotranspiration and Crop Growth of Irrigated and Non-Irrigated Corn in the Texas High Plains Using RZWQM

2018 ◽  
Vol 61 (5) ◽  
pp. 1653-1666 ◽  
Author(s):  
Huihui Zhang ◽  
Robert Wayne Malone ◽  
Liwang Ma ◽  
Lajpat R. Ahuja ◽  
Saseendran S. Anapalli ◽  
...  
Keyword(s):  
Water Stress ◽  
Soil Water ◽  
Crop Production ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Water Productivity ◽  
Stress Factors ◽  
Irrigated Agriculture ◽  
High Plains ◽  
Area Index

Abstract. Accurate quantification and management of crop evapotranspiration (ET) are critical to optimizing crop water productivity for both dryland and irrigated agriculture, especially in the semiarid regions of the world. In this study, four weighing lysimeters in Bushland, Texas, were planted to maize in 1994 with two fully irrigated and two non-irrigated for measuring crop ET. The Root Zone Water Quality Model (RZWQM2) was used to evaluate soil water balance and crop production with potential evapotranspiration (PET) estimated from either the Shuttleworth-Wallace method (PTSW) or the ASCE standardized alfalfa reference ET multiplied by crop coefficients (PTASCE). As a result, two water stress factors were defined from actual transpiration (AT) and were tested in the model against the lysimeter data, i.e., AT/PTSW and AT/PTASCE. For both water stress factors, the simulated daily ET values were reasonably close to the measured values, with underestimated ET during mid-growing stage in both non-irrigated lysimeters. Root mean squared deviations (RMSDs) and relative RMSDs (RMSD/observed mean) values for leaf area index, biomass, soil water content, and daily ET were within simulation errors reported earlier in the literature. For example, the RMSDs of simulated daily ET were less than 1.52 mm for all irrigated and non-irrigated lysimeters. Overall, ET was simulated within 3% of the measured data for both fully irrigated lysimeters and undersimulated by less than 11% using both stress factors for the non-irrigated lysimeters. Our results suggest that both methods are promising for simulating crop production and ET under irrigated conditions, but the methods need to be improved for dryland and non-irrigated conditions. Keywords: ET, RZWQM modeling, Stress factor, Weighing lysimeter.

TRANSPIRATION RATE OF DOUGLAS FIR TREES IN THINNED AND UNTHINNED STANDS

1980 ◽  
Vol 60 (4) ◽  
pp. 625-631 ◽  
Author(s):  
T. A. BLACK ◽  
U. NNYAMAH ◽  
C. S. TAN
Keyword(s):  
Soil Water ◽  
Transpiration Rate ◽  
Root Zone ◽  
Douglas Fir ◽  
Understory Vegetation ◽  
Diameter Growth ◽  
Tree Diameter ◽  
Evapotranspiration Rate ◽  
Sunny Weather ◽  
Extractable Soil

A procedure is described for estimating the transpiration rate of trees in stands with understory vegetation. The procedure combines soil water balance measurements of stand evapotranspiration rate with a simple vapor diffusion model that requires occasional intensive measurements of stomatal conductance of the trees and understory vegetation. Weekly average transpiration rates of 22-yr-old Douglas fir trees in a thinned stand during sunny weather in July ranged from 23.6 L∙tree−1∙d−1 when θe the fraction of extractable soil water remaining in the root zone, was 0.79 to 4.9 L∙tree−1∙d−1 when θe was 0.20. The transpiration rate of trees in the thinned stand, which contained a salal understory, was very similar to that in a nearby unthinned stand with virtually no understory vegetation. As θe decreased from slightly more than 0.8 to slightly less than 0.2, the fraction of evapotranspiration from the thinned stand due to the salal understory increased from approximately 40 to 65%. Competition for soil water by the understory was considered to be a contributing reason why tree diameter growth in the thinned stand was only slightly greater than in the unthinned stand.

Modelling water uptake by a mature apple tree

Soil Research ◽  
2003 ◽  
Vol 41 (3) ◽  
pp. 365 ◽  
Author(s):  
S. R. Green ◽  
I. Vogeler ◽  
B. E. Clothier ◽  
T. M. Mills ◽  
C. van den Dijssel
Keyword(s):  
Experimental Data ◽  
Water Content ◽  
Soil Water ◽  
Water Uptake ◽  
Apple Tree ◽  
Water Movement ◽  
Root Zone ◽  
Time Domain Reflectometry ◽  
Richards Equation ◽  
Mature Apple

We report the results from a field experiment in which we examined the spatial and temporal patterns of water uptake by a mature apple tree (Malus domestica Borkh., 'Splendour') in an orchard. Time domain reflectometry was used to measure changes in the soil's volumetric water content, and heat-pulse was used to monitor locally the rates of sap flow in the trunk and roots of the tree. The tree's distribution of root-length density and supporting data to characterise the soil's hydraulic properties were determined for the purpose of modelling soil water movement in the root-zone under an apple tree. Experimental data are compared against the output from a numerical model of the soil water balance that uses Richards' equation for water flow, and uses a distributed macroscopic sink term for root uptake. In general, there was a very good agreement between the measured and modelled results. The apple trees consumed some 70 L of water per day during the middle of summer. The daily water use declined to about 20 L per day with the onset of autumn, coinciding with a reduced evaporative demand and an increasing number of rain days. Water movement in the root-zone soil was dominated by the water uptake via surface roots. Large changes in soil water content were also associated with each irrigation event. Our experimental data support the contention that more frequent irrigation in smaller doses will result in less water percolating through the root-zone. Such an irrigation strategy should make more efficient use of water by minimising the leaching losses. It will also be helpful for environmental protection by reducing the percolation losses of water and solute beyond the grasp of the roots.

scholarly journals Calculation of available water supply in crop root zone and the water balance of crops

2015 ◽  
Vol 45 (4) ◽  
pp. 285-298 ◽  
Author(s):  
Jan Haberle ◽  
Pavel Svoboda
Keyword(s):  
Water Balance ◽  
Water Supply ◽  
Soil Water ◽  
Root Zone ◽  
Potential Evapotranspiration ◽  
Pedotransfer Functions ◽  
Soil Water Retention ◽  
Available Water ◽  
Available Water Content ◽  
Access To Data

Abstract Determination of the water supply available in soils for crops is important for both the calculation of water balance and the prediction of water stress. An approach to calculations of available water content in layers of the root zone, depletion of water during growth, and water balance, with limited access to data on farms, is presented. Soil water retention was calculated with simple pedotransfer functions from the texture of soil layers, root depth, and depletion function were derived from observed data; and the potential evapotranspiration was calculated from the temperature. A comparison of the calculated and experimental soil water contents showed a reasonable fit.

Factors affecting the growth of kikuyu. II. Water supply

1988 ◽  
Vol 39 (1) ◽  
pp. 43
Author(s):  
GJ Murtagh
Keyword(s):  
Water Supply ◽  
Water Potential ◽  
Soil Water ◽  
Potential Evapotranspiration ◽  
Soil Water Potential ◽  
Field Measurements ◽  
Light Interception ◽  
Maintenance Respiration ◽  
Evaporative Demand ◽  
Factors Affecting

The influence of water supply on the growth of a kikuyu (Pennisetum clandestinum) pasture was estimated from field measurements of growth rate. A model was used to separate the confounded effects on growth of light interception, temperature, nitrogen and water supplies, and maintenance respiration. Water supply for growth was expressed as a function of both the soil water content and evaporative demand (potential evapotranspiration). The growth of kikuyu was very sensitive to water supply. On a wet soil (soil water potential > -20 kPa), an evaporative demand above 3.2 mm day-1 slowed growth. With optimum temperatures and a sward yield which gave the best balance between light interception and rate of maintenance respiration, a low evaporative demand of 2 mm day-1 reduced growth rates only when the soil water potential was less than - 134 kPa. However, with a medium-high evaporative demand of 5 mm day-1, growth was reduced by 39% on a wet soil, and ceased at a soil water potential of - 101 kPa.

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