Influence of Soil Water Potential and Atmospheric Evaporative Demand on Transpiration and the Energy Status of Water in Plants
            1

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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Soil–Water–Vine Relationships and Water Management

Soils for Fine Wines ◽

10.1093/oso/9780195141023.003.0008 ◽

2003 ◽

Author(s):

Robert E. White

Keyword(s):

Free Energy ◽

Potential Energy ◽

Water Potential ◽

Soil Water ◽

Soil Water Potential ◽

Water Molecules ◽

Measured Quantity ◽

Energy Status ◽

Charged Surfaces ◽

Cell Turgor

Water is a prerequisite for vine growth. It is essential for photosynthesis and to maintain the hydrated conditions and cell turgor necessary for a host of other biochemical processes in the plant. As we saw in chapter 4, diffusion of nutrient ions to the root, and their movement by mass flow into the vine’s “transpiration stream,” both depend on water. The volumetric water content θ, defined as the volume of water per unit volume of soil (section 3.3.2), indicates how much water the soil can hold. However, to understand what drives water movement in the soil, we must understand the forces acting on the water because they affect its potential energy. The energy status of soil water also influences its availability to plants. There is no absolute scale of potential energy. But we can measure changes in potential energy when useful work is done on a measured quantity of water or when the water itself does useful work. These changes are observed as changes in the free energy of water, which gives rise to the concept of soil water potential. The derivation of the soil water potential ψ (psi) is given in appendix 7. Historically, the energy status of soil water has been described by a number of terms related to soil water potential, such as pressure, suction, or hydraulic head. These terms ψ and their units are explained in box 6.1. The terms and head will be used in this book. Several forces act on soil water to decrease its free energy and give rise to component potentials. These are adsorption forces, capillary forces, osmotic forces, and gravity. Adsorption Forces. In very dry soils (relative humidity, RH, of the soil air <20%), water is adsorbed onto the clay and silt particles as a monolayer in which the molecules are hydrogen bonded to each other and the surface. With an increase in RH, more water molecules are adsorbed by hydrogen bonding to those on the surface. The charged surfaces of clay minerals also attract cations, and the electric field of the cation orients the polar water molecules around the ion to form a hydration shell, containing 6–12 water molecules.

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Effect of Soil Water Potential of Two Soils on Soybean Emergence 1

Agronomy Journal ◽

10.2134/agronj1979.00021962007100060021x ◽

1979 ◽

Vol 71 (6) ◽

pp. 980-982 ◽

Cited By ~ 3

Author(s):

L. G. Heatherly ◽

W. J. Russell

Keyword(s):

Water Potential ◽

Soil Water ◽

Soil Water Potential

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Simulating sunflower canopy temperatures to infer root-zone soil water potential

Agricultural and Forest Meteorology ◽

10.1016/0168-1923(84)90007-8 ◽

1984 ◽

Vol 31 (1) ◽

pp. 69-78 ◽

Cited By ~ 8

Author(s):

Bhaskar J. Choudhury ◽

Sherwood B. Idso

Keyword(s):

Water Potential ◽

Soil Water ◽

Root Zone ◽

Soil Water Potential

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A Data-Driven Method for the Temporal Estimation of Soil Water Potential and Its Application for Shallow Landslides Prediction

Water ◽

10.3390/w13091208 ◽

2021 ◽

Vol 13 (9) ◽

pp. 1208

Author(s):

Massimiliano Bordoni ◽

Fabrizio Inzaghi ◽

Valerio Vivaldi ◽

Roberto Valentino ◽

Marco Bittelli ◽

...

Keyword(s):

Machine Learning ◽

Water Potential ◽

Soil Water ◽

Temporal Trends ◽

Soil Water Potential ◽

Shallow Landslides ◽

Water Dynamics ◽

Data Driven ◽

Machine Learning Techniques ◽

Physically Based

Soil water potential is a key factor to study water dynamics in soil and for estimating the occurrence of natural hazards, as landslides. This parameter can be measured in field or estimated through physically-based models, limited by the availability of effective input soil properties and preliminary calibrations. Data-driven models, based on machine learning techniques, could overcome these gaps. The aim of this paper is then to develop an innovative machine learning methodology to assess soil water potential trends and to implement them in models to predict shallow landslides. Monitoring data since 2012 from test-sites slopes in Oltrepò Pavese (northern Italy) were used to build the models. Within the tested techniques, Random Forest models allowed an outstanding reconstruction of measured soil water potential temporal trends. Each model is sensitive to meteorological and hydrological characteristics according to soil depths and features. Reliability of the proposed models was confirmed by correct estimation of days when shallow landslides were triggered in the study areas in December 2020, after implementing the modeled trends on a slope stability model, and by the correct choice of physically-based rainfall thresholds. These results confirm the potential application of the developed methodology to estimate hydrological scenarios that could be used for decision-making purposes.

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NITROGEN TRANSFORMATIONS NEAR UREA IN SOIL WITH DIFFERENT WATER POTENTIALS

Canadian Journal of Soil Science ◽

10.4141/cjss88-055 ◽

1988 ◽

Vol 68 (3) ◽

pp. 569-576 ◽

Cited By ~ 14

Author(s):

YADVINDER SINGH ◽

E. G. BEAUCHAMP

Keyword(s):

Water Potential ◽

Soil Water ◽

Incubation Period ◽

Relative Rate ◽

Soil Water Potential ◽

Nitrification Inhibitor ◽

Silt Loam ◽

Nitrogen Transformations ◽

Water Potentials ◽

Initial Soil

Two laboratory incubation experiments were conducted to determine the effect of initial soil water potential on the transformation of urea in large granules to nitrite and nitrate. In the first experiment two soils varying in initial soil water potentials (− 70 and − 140 kPa) were incubated with 2 g urea granules with and without a nitrification inhibitor (dicyandiamide) at 15 °C for 35 d. Only a trace of [Formula: see text] accumulated in a Brookston clay (pH 6.0) during the transformation of urea in 2 g granules. Accumulation of [Formula: see text] was also small (4–6 μg N g−1) in Conestogo silt loam (pH 7.6). Incorporation of dicyandiamide (DCD) into the urea granule at 50 g kg−1 urea significantly reduced the accumulation of [Formula: see text] in this soil. The relative rate of nitrification in the absence of DCD at −140 kPa water potential was 63.5% of that at −70 kPa (average of two soils). DCD reduced the nitrification of urea in 2 g granules by 85% during the 35-d period. In the second experiment a uniform layer of 2 g urea was placed in the center of 20-cm-long cores of Conestogo silt loam with three initial water potentials (−35, −60 and −120 kPa) and the soil was incubated at 15 °C for 45 d. The rate of urea hydrolysis was lowest at −120 kPa and greatest at −35 kPa. Soil pH in the vicinity of the urea layer increased from 7.6 to 9.1 and [Formula: see text] concentration was greater than 3000 μg g−1 soil. There were no significant differences in pH or [Formula: see text] concentration with the three soil water potential treatments at the 10th day of the incubation period. But, in the latter part of the incubation period, pH and [Formula: see text] concentration decreased with increasing soil water potential due to a higher rate of nitrification. Diffusion of various N species including [Formula: see text] was probably greater with the highest water potential treatment. Only small quantities of [Formula: see text] accumulated during nitrification of urea – N. Nitrification of urea increased with increasing water potential. After 35 d of incubation, 19.3, 15.4 and 8.9% of the applied urea had apparently nitrified at −35, −60 and −120 kPa, respectively. Nitrifier activity was completely inhibited in the 0- to 2-cm zone near the urea layer for 35 days. Nitrifier activity increased from an initial level of 8.5 to 73 μg [Formula: see text] in the 3- to 7-cm zone over the 35-d period. Nitrifier activity also increased with increasing soil water potential. Key words: Urea transformation, nitrification, water potential, large granules, nitrifier activity, [Formula: see text] production

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