scholarly journals The course, stratification and possibility of simulating relative air humidity in winter wheat stand

2016 ◽  
Vol 46 (2) ◽  
pp. 137-154
Author(s):  
Jana Krčmářová ◽  
Radovan Pokorný ◽  
Tomáš Středa
Keyword(s):  
Regression Analysis ◽  
Winter Wheat ◽  
Soil Water ◽  
Potential Evapotranspiration ◽  
Soil Water Potential ◽  
Air Humidity ◽  
Field Station ◽  
Effective Height ◽  
Relative Air Humidity ◽  
Climatological Station

AbstractThe aim of this study was: (i) long-term (2010, 2011 and 2013) evaluation of the relative air humidity in the winter wheat canopy, (ii) finding of relationships between relative air humidity in canopy and computed or measured meteorological values (precipitation totals, evapotranspiration, moisture balance, specific air humidity, volume soil moisture, % of available soil water content, value of soil water potential), (iii) testing of simulation of daily relative air humidity, based on selected meteorological values and potential evapotranspiration (FAO Penman-Monteith method) and actual evapotranspiration, (iv) testing of simulation of relative air humidity hourly values in the wheat canopy, (v) evaluation of dependence between relative air humidity and leaf wetness. The measurement was performed at the experimental field station of Mendel University in Žabčice (South Moravia, the Czech Republic). Data recording for wheat canopy was conducted by means of a meteostation equipped with digital air humidity and air temperature sensors positioned in the ground, effective height of the stand and in 2 m above the ground. The main vegetation period of wheat was divided into three stages to evaluate differences in various growing phases of wheat. The data from nearby standard climatological stations and from agrometeorological station in Žabčice were used for establishment of relationships between relative air humidity in winter wheat canopy and surrounding environment by correlation and regression analysis. Relative air humidity above 90% occurred substantially longer on the ground and at the effective height of the stand in comparison with the height of 2 m. By means of regression analysis we determined that the limit of 90% was reached in the canopy when at the climatological station it was just 60 to 90% for ground level and 70 to 90% for effective height, especially during the night. Slight dependence between measured or computed meteorological variables and relative air humidity in winter wheat canopy was found (r= 0.23 − 0.56 for precipitation totals,r= 0.27 − 0.57 for % of available soil water capacity, etc.). The simulation of hourly values of relative air humidity in wheat canopy is partially possible just when using the data of relative air humidity from the relevant standard climatological station.

scholarly journals Microclimate in the vertical profile of wheat, rape and maize canopies

2012 ◽  
Vol 60 (1) ◽  
pp. 79-90 ◽  
Author(s):  
Zdeněk Krédl ◽  
T. Středa ◽  
R. Pokorný ◽  
M. Kmoch ◽  
J. Brotan
Keyword(s):  
Air Temperature ◽  
Vertical Profile ◽  
Soil Surface ◽  
Ground Level ◽  
Air Humidity ◽  
Winter Rape ◽  
Effective Height ◽  
Relative Air Humidity ◽  
Climatological Station ◽  
South Moravia

The differences of air temperature and relative air humidity in wheat, rape and maize canopies at three heights (ground level, effective canopy height and 2 meters above the soil surface), and their comparison with the temperature values of the nearest standard climatological station at the height of 2 meters were studied. The microclimatic data were obtained at the field trial station of the Mendel University in Brno in the Žabčice municipality (South Moravia) in the canopies of winter wheat, winter rape and maize and from the standard climatological station located immediately next to the canopies. It was found, that wheat, rape and maize canopies microclimate differed significantly from those of their surrounding environments. The temperature was usually lower in the ground level and effective height in the wheat and rape stands, air humidity was usually higher in these crops. On the other hand, maize canopies had diverse air temperature values during the studied period.

Water relations of winter wheat. 5. The root system and osmotic adjustment in relation to crop evaporation

1984 ◽  
Vol 102 (2) ◽  
pp. 415-425 ◽  
Author(s):  
M. McGowan ◽  
P. Blanch ◽  
P. J. Gregory ◽  
D. Haycock
Keyword(s):  
Winter Wheat ◽  
Water Potential ◽  
Root System ◽  
Soil Water ◽  
Osmotic Adjustment ◽  
Stomatal Closure ◽  
Soil Water Potential ◽  
Plant Water ◽  
Potential Evaporation ◽  
Plant Water Potential

SummaryShoot and root growth and associated leaf and soil water potential relations were compared in three consecutive crops of winter wheat grown in the same field. Despite a profuse root system the crop grown in the second drought year (1976) failed to dry the soil as throughly as the crops in 1975 and 1977. Measurements of plant water potential showed that the restricted utilization of soil water reserves by this crop was associated with failure to make any significant osmotic adjustment, leading to premature loss of leaf turgor and stomatal closure. The implications of these results for models to estimate actual crop evaporation from values of potential evaporation are discussed.

Water relations of winter wheat: 2. Soil water relations

1978 ◽  
Vol 91 (1) ◽  
pp. 103-116 ◽  
Author(s):  
P. J. Gregory ◽  
M. McGowan ◽  
P. V. Biscoe
Keyword(s):  
Winter Wheat ◽  
Water Potential ◽  
Soil Water ◽  
Water Relations ◽  
Unit Length ◽  
Soil Water Potential ◽  
Rooting Depth ◽  
Wheat Crop ◽  
Deep Roots ◽  
Volumetric Soil Water Content

SummaryVolumetric soil water content and soil water potential were measured beneath a winter wheat crop during the 1975 growing season. Almost no rain fell between mid-May and mid-July and the soil dried continuously until the potential was less than – 20 bars to a depth of 80 cm. Evaporation was separated from drainage by denning an ‘effective rooting depth’ at which the hydraulic gradient was zero.Rates of water uptake per unit length of root (inflow) were calculated for the whole soil profile and for individual soil layers. Generally, inflow decreased throughout the period of measurement from a maximum of 2·5 × 10–3 to a minimum of 0·66 × 10–3 ml water/cm root/day. Values in individual layers were frequently higher than the mean inflow and the importance of a few deep roots in taking up water during a dry season is emphasized. A similar correlation between inflow and soil water potential was found to apply for the 0–30 cm and 30–60 cm layers during the period of continual soil drying. This relationship represents the maximum inflow measured at a given soil water potential; actual inflow at any particular time depends upon the interrelationship of atmospheric demand, soil water potential and the distribution of root length in the soil.

Water relations of winter wheat: 3. Components of leaf water potential and the soil-plant water potential gradient

1983 ◽  
Vol 100 (3) ◽  
pp. 581-589 ◽  
Author(s):  
J. S. Wallace ◽  
J. A. Clark ◽  
M. McGowan
Keyword(s):  
Water Stress ◽  
Winter Wheat ◽  
Water Potential ◽  
Soil Water ◽  
Soil Water Potential ◽  
Potential Gradient ◽  
Potential Drop ◽  
Root Surface ◽  
Total Water ◽  
Leaf Osmotic Potential

SUMMARYDiurnal and seasonal changes in the total, osmotic and turgor potentials of winter wheat leaves are compared in two seasons of mild and severe soil water stress. Gradients of total water potential in the soil-plant system are also presented. In both seasons the total water potential of the leaves decreased in parallel with the soil water potential, concurrently leaf osmotic potential also decreased sufficiently to maintain positive leaf turgor potential. Eventually, under severe water stress, soil water potential approached –1·5 MPa and leaf turgor potential tended to zero during the middle of the day.The potential drop across the soil-root system was twice that along the stem. Estimates of the water potential at the root surface varied diurnally and were often lower than the bulk soil water potential. In dry soil plants were unable to equilibrate with the soil water potential overnight. These results are consistent with the existence of significant resistance to water flow across the rhizosphere.

scholarly journals Germination of rye brome (Bromus secalinus L.) seeds under simulated drought and different thermal conditions

2014 ◽  
Vol 66 (4) ◽  
pp. 157-164
Author(s):  
Małgorzata Haliniarz ◽  
Jan Kapeluszny ◽  
Sławomir Michałek
Keyword(s):  
Polyethylene Glycol ◽  
Water Potential ◽  
Soil Water ◽  
Soil Water Potential ◽  
Gravimetric Method ◽  
Thermal Conditions ◽  
Initial Growth ◽  
Air Humidity ◽  
Bromus Secalinus ◽  
Simulated Drought

The aim of the present study was to compare the germination of rye brome (<em>Bromus secalinus </em>L.) seeds and the initial growth of seedlings under simulated drought and different thermal conditions. The study included two experiments carried out under laboratory conditions in the spring of 2012. The first experiment involved an evaluation of the speed of germination as well as of the biometric characters and weight of seedlings in polyethylene glycol solutions (PEG 8000) in which the water potential was: -0.2; -0.4; -0.65; -0.9 MPa, and in distilled water as the control treatment. The experiment was conducted at the following temperatures: 25/22oC and 18/14oC day/night, at a relative air humidity of 90%. The other experiment, in which lessive soil was used as a germination substrate, was carried out in a plant growth chamber at two levels of air humidity (55–65% and 85–95%) and temperature (22/10oC and 16/5oC). The soil moisture content was determined by the gravimetric method and the water potential corresponding to it was as follows: -0.02, -0.07, -0.16, -0.49, -1.55 MPa. The germination capacity and emergence of <em>Bromus secalinus </em>as well as the weight of sprouts produced were significantly dependent on the water potential of the polyethylene glycol solution and on the soil water potential. The emergence of <em>Bromus secalinus </em>was completely inhibited by reducing the soil water potential below -0.16 MPa (the point of strong growth inhibition). The emergence and biometric characters of rye bro- me seedlings were significantly dependent on temperature and air humidity.

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.

scholarly journals Horizontal soil water potential heterogeneity: simplifying approaches for crop water dynamics models

2014 ◽  
Vol 11 (1) ◽  
pp. 1203-1252 ◽  
Author(s):  
V. Couvreur ◽  
J. Vanderborght ◽  
L. Beff ◽  
M. Javaux
Keyword(s):  
Analytical Solution ◽  
Winter Wheat ◽  
Water Potential ◽  
Soil Water ◽  
Soil Water Potential ◽  
Water Dynamics ◽  
Implicit Assumption ◽  
Plant Water ◽  
Row Crops ◽  
D Model

Abstract. Soil water potential (SWP) is known to affect plant water status, and even though observations demonstrate that SWP distribution around roots may limit plant water availability, its horizontal heterogeneity within the root zone is often neglected in hydrological models. As motive, using a horizontal discretisation significantly larger than one centimetre is often essential for computing time considerations, especially for large scale hydrodynamics models. In this paper, we simulate soil and root system hydrodynamics at the centimetre scale and evaluate approaches to upscale variables and parameters related to root water uptake (RWU) for two crop systems: a densely seeded crop with an average uniform distribution of roots in the horizontal direction (winter wheat) and a wide-row crop with lateral variations in root density (maize). In a first approach, the upscaled water potential at soil–root interfaces was assumed to equal the bulk SWP of the upscaled soil element. Using this assumption, the 3-D high resolution model could be accurately upscaled to a 2-D model for maize and a 1-D model for wheat. The accuracy of the upscaled models generally increased with soil hydraulic conductivity, lateral homogeneity of root distribution, and low transpiration rate. The link between horizontal upscaling and an implicit assumption on soil water redistribution was demonstrated in quantitative terms, and explained upscaling accuracy. In a second approach, the soil–root interface water potential was estimated by using a constant rate analytical solution of the axisymmetric soil water flow towards individual roots. In addition to the theoretical model properties, effective properties were tested in order to account for unfulfilled assumptions of the analytical solution: non-uniform lateral root distributions and transient RWU rates. Significant improvements were however only noticed for winter wheat, for which the first approach was already satisfying. This study confirms that the use of 1-D spatial discretisation to represent soil-plant water dynamics is a worthy choice for densely seeded crops. For wide-row crops, e.g. maize, further theoretical developments that better account for horizontal SWP heterogeneity might be needed in order to properly predict soil-plant hydrodynamics in 1-D.

Water Relations of Winter Wheat: the Root System, Petiolar Resistance and Development of a Root Abstraction Equation

1985 ◽  
Vol 21 (4) ◽  
pp. 377-388 ◽  
Author(s):  
M. McGowan ◽  
E. Tzimas
Keyword(s):  
Winter Wheat ◽  
Root System ◽  
Soil Water ◽  
Water Uptake ◽  
Water Relations ◽  
Field Experiments ◽  
Soil Water Potential ◽  
Root Systems ◽  
Wheat Crop ◽  
Winter Wheat Crop

SUMMARYThe vertical distribution of water potentials within the leaf canopy, along the stem and within the soil profile of a winter wheat crop was analysed and it is concluded the failure by previous workers to recognize the significance of petiolar resistance has probably resulted in over-estimates of the resistance of the soil to water uptake by root systems of field crops.From an analysis of the water relations of several winter wheat crops an equation is developed to describe the extraction of soil water reserves by crop root systems, based upon values of soil water potential, root xylem potential and ‘effective’ resistance to water uptake which can be obtained from field experiments. The equation provides an empirical basis to specify the minimum desirable root system for efficient capture of soil water reserves, to analyse the effects of differing root distributions and thus to help identify situations where it would be profitable to modify rooting either by tillage or by plant breeding.

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