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1.
Summary Four melon (Cucumis melo L.) cultivars were tested for salt tolerance at germination, seedling growth stages, and plant maturation. Noy Amid was the most tolerant during germination, achieving 56% germination in 15,000 mg/l NaCl solution. However, this cultivar and Eshkolit Ha 'Amaqim were relatively sensitive during the first 4 days' growth of the radicle and the hypocotyl, and the first 3 weeks' development of the seedling. Their yields were reduced under saline as compared with non-saline field conditions. In contrast, Honey Dew and Rochet had little or no germination in 15,000 mg/l NaCl but showed salt tolerance during seedling growth stages. Yield of Honey Dew was unaffected by saline field conditions, and that of Rochet was not significantly reduced from the non-saline control. Thus, selection for salt tolerance in melons appears feasible during early vegetative growth stages but not during germination.Contribution No. 1032-E, 1984 series, from the Agricultural Research Organization, Bet Dagan, Israel 相似文献
2.
Summary Seed-cotton yield, yield components and vegetative growth were determined under different irrigation frequencies and wetting depths with a self-propelled moving-irrigation-system (MSIS) in 1986 and 1987. Irrigation timing was determined in both years by pre-irrigation, mid-day plant water potential (w). The amount of water to be applied was determined by measuring the soil moisture deficit. In 1987, the effect of a change from one irrigation frequency and wetting depth to another at mid-flowering was also examined. Linear responses of relative seed-cotton yield to the amount of evapotranspiration (ET) were found for both years with similar slopes but different intercepts. Significant positive regressions were obtained between pre-irrigation plant w and relative seed-cotton yield, and vegetative growth during the linear growth stage. Seed-cotton yield was affected by both wetting depth and pre-irrigation plant w. The deeper the irrigation the higher was the seed-cotton yield for each pre-irrigation plant w. Irrigation frequencies which maintained plant w above -1.5 MPa during vegetative growth, flowering and boll-filling resulted in maximum production. The boll filling stage appeared to be a very sensitive one, as boll weight was found to be the main yield component responding to irrigation treatments. At a wetting depth of 120 cm, higher seed-cotton yields were obtained than at a more shallow wetting. Different irrigation managements resulted in different turgor potentials (t) mainly during mid-day. Both leaf water vapour conductance and net assimilation rate were sensitive to leaf w.Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagon, Israel, No. 2903-E, 1990 series. Research was supported by the U.S.-Israel Binational Agric. Res. and Develop. Fund. 相似文献
3.
J. B. Prendergast 《Irrigation Science》1993,13(4):157-164
A relationship between crop yield and irrigation water salinity is developed. The relationship can be used as a production function to quantify the economic ramifications of practices which increase irrigation water salinity, such as disposal of surface and sub-surface saline drainage waters into the irrigation water supply system. Guidelines for the acceptable level of irrigation water salinity in a region can then be established. The model can also be used to determine crop suitability for an irrigation region, if irrigation water salinity is high. Where experimental work is required to determine crop yield response to irrigation water salinity, the model can be used as a first estimate of the response function. The most appropriate experimental treatments can then be allocated. The model adequately predicted crop response to water salinity, when compared with experimental data.Abbreviations A
Crop threshold rootzone salinity in Equation of Maas and Hoffman (dS/m)
- B
Fractional yield reduction per unit rootzone salinity increase (dS/m)–1
- Ci
Average salinity of applied water (dS/m)
- Cr
Average salinity of rainfall (dS/m)
- Cs
Linearly averaged soil solution salinity in the rootzone (dS/m)
- Cse
Linearly averaged soil saturation extract salinity in the rootzone (dS/m)
- Cw
Average salinity of irrigation supply water (dS/m)
- Cz
Soil solution salinity at the base of the crop rootzone (dS/m)
- C
Mean root water uptake weighted soil salinity in equation of Bernstein and François (1973) (dS/m)
- Ep
Depth of class A pan evaporation during the growing season (m)
- ETa
Actual crop evapotranspiration during the growing season (m)
- ETm
Maximum crop evapotranspiration during the growing season (m)
- I
The total depth of water applied during the growing season (including irrigation water and rainfall) (m)
- K
Empirical coefficient in leaching equation of Rhoades (1974)
- Kc
Crop coefficient for equation of Doorenbos and Pruit (1977) to estimate crop water use
- Ky
Yield response factor in equation of Doorenbos and Kassam (1974)
- LF
The leaching fraction
- Ro
Depth of rainfall runoff during the growing season (m)
- R
Depth of rainfall during the growing season (m)
- W
Depth of irrigation water applied during the growing season (m)
- Y
Relative crop yield
- Ya
Actual crop yield (kg)
- Ym
Maximum crop yield (kg)
-
/z
Dimensionless depth for equation of Raats (1974), and empirical coefficient for the leaching equation of Hoffman and van Genutchen (1983) 相似文献
4.
The legal-administrative setting for the use of waterresources in Mendoza Province is founded on differentlegal rules. This includes the National Constitution,the Argentine Civil Code, National Laws, theConstitution of the Provincial State, the GeneralWater Law, (legal) administrative regulations of theGeneral Department of Irrigation.The current water law is based on the roman law, onthe Arab irrigation water rights which were brought toArgentina by the Spaniards and on the practices of theoriginal American pre-Colombian intermediate law.The latter is marked by a strong regional sense. Assuch, the water law is strongly influenced by theregions elements of nature and attempts to offersolutions to problems.The legal rules are discussed from a behavioral andorganizational perspective. Examples from the LowerTunuyan System are given to illustrate the day-to-dayeffects on irrigation water management. 相似文献
5.
Summary The interaction of different K status of barley plants (Hordeum vulgare, L.) and water stress on yield and water relations was studied. The plants which were cultivated outdoor in pots and supplied with 0.8, 5.0, 8.5 or 12.0 g K per pot, as KCl, were subjected to increased soil water stress during the early grain filling stage.The water content of the flag leaf tissue was significantly increased from 3.1 to 4.1 g H2O/g D.M. (dry matter) by K application resulting in maintenance of similar leaf osmotic potentials (–1.5 MPa) at all K levels prior to onset of water stress (Table 2). At the lowest K level Ca contributed essentially to maintenance of the cell osmotic potential (Fig. 2).In fully watered plants grain yield at the lowest K level was reduced 20% (Fig. 5 a) due to a decrease in the number of tillers with ears per plant (Fig. 5 b) and to early commencement of maturity processes (Table 3).Water stress caused grain yield reductions between 15 and 50%. However, by increase of K application yield was maintained to the greatest degree in high K plants (Fig. 5 a) due to improved water status in these plants during the drying cycle (Fig. 4). The production of above ground dry matter (top D.M.) during the grain filling period and the grain yield were highly correlated with the leaf water content at the end of the drying cycles (Fig. 6). The greater yield in high K plants was associated with prolongation of the grain filling period by up to 7 days (Table 3) and with an increase in grain weight by up to 20% (Fig. 5 b) as compared with low K plants. Preanthesis reserves contributed up to 52% of grain yield at low K levels (Fig. 5 c) reducing differences in grain yield between the K levels.Abbreviations RWC
predawn relative water content
-
predawn leaf osmotic potential
- WUE
water use efficiency
- R
preanthesis reserves
- ear D.M.
increase in ear D.M. during the grain filling period
- top D.M.
increase in top D.M. during the grain filling period
- SD
standard deviation
- LSD
least significant difference 相似文献
6.
C. R. Jensen 《Irrigation Science》1982,3(2):111-121
Summary Barley plants (Hordeum distichum, L., cv. Zita) grown in a sandy soil in pots were adjusted during a pretreatment period of 5 days to three levels of soil water osmotic potential by percolating 61 of a nutrient solution with additional 0, 22.3 and 44.6 mM KCl. A drying cycle was then started and the plants were harvested when the soil water matric potential had decreased to –1.4 MPa, respectively 6, 7 and 8 days later.No significant differences in dry matter yields, transpiration coefficients and wilting percentages were found between treatments.During the drying cycle leaf water potential (
l
) decreased concomitantly with decrease in soil water potential (
s
) with almost constant and similar differences (
l
–
s
) for all treatments despite differences in levels of potentials. The concomitant decrease in leaf osmotic potential () was due partly to dehydration (58%) and partly to increase in leaf solute content (42%) independent of treatment. The part of total osmotic solutes due to K decreased relatively during the drying cycle.Close relationships were found between and
l
as functions of relative water content (RWC). Identical curves for the two levels of salt treatment agree with similar concentrations of K, Cl, and ash found for salt treated plants indicating that maximum uptake of macro nutrients may have been reached.During the main part of the drying cycle the turgor potential as function of RWC was higher and decreased less steeply with decreasing RWC in the salt treated than in the non-salt treated plants.In the beginning of the drying cycle additions of KCI lowered the transpiration rates of the salt treated plants resulting in a slower desiccation of the soil and hence an increased growth period. A delay in uptake from a limited soil water supply may be advantageous during intermittent periods of drought. 相似文献
7.
Summary The growth response of kenaf (Hibiscus cannabinus L.) to four irrigation schedules based on leaf water potential l was evaluated in a semi-arid tropical environment. Total dry matter production was unaffected by regimes in which the mean value of leaf water potential l (mean of solar noon and dawn value) did not fall below –1.26 MPa. Stem elongation was more sensitive than dry matter accumulation to plant water stress. — The economic yield for paper pulp production (i. e. total plant dry matter production minus that of the foliage and upper 60 cm of stem) increased with the frequency of irrigation. — Growth recovery by kenaf following a period of water stress was examined. Alleviation of water stress 10 weeks after irrigation, when l was –1.60 MPa, produced stem elongation rates that were greater than those of plants previously receiving irrigation. This ability to withstand water stress and partially compensate in growth following alleviation of the stress indicates that the kenaf crop has stress response features suitable for rainfall only production under semi-arid tropical conditions. — Irrigation schedules based on l resulted in water applications tailored to crop requirements in that water use increased, and the time interval between irrigation decreased, with increasing canopy development as well as with increasing evaporative demand. However, erratic fluctuations in l between irrigations make scheduling by this method difficult and the use of daily mean, dawn or noon values of l for scheduling irrigation of kenaf cannot be recommended in environments of high evaporative demand. The factors contributing to these fluctuations in (l) are discussed. 相似文献
8.
Summary The Lewis-Milne (LM) equation has been widely applied for design of border irrigation systems. This equation is based on the concept of mass conservation while the momentum balance is replaced by the assumption of a constant surface water depth. Although this constant water depth depends on the inflow rate, slope and roughness of the infiltrating surface, no explicit relation has been derived for its estimation. Assuming negligible border slope, the present study theoretically treats the constant depth in the LM equation by utilizing the simple dam-break wave solution along with boundary layer theory. The wave front is analyzed separately from the rest of the advancing water by considering both friction and infiltration effects on the momentum balance. The resulting equations in their general form are too complicated for closed-form solutions. Solutions are therefore given for specialized cases and the mean depth of flow is presented as a function of the initial water depth at the inlet, the surface roughness and the rate of infiltration. The solution is calibrated and tested using experimental data.Abbreviations
a (t)
advance length
-
c
mean depth in LM equation
-
c
f
friction factor
-
c
h
Chezy's friction coefficient
-
g
acceleration due to gravity
-
h(x, t)
water depth
-
h
0
water depth at the upstream end
-
i()
rate of infiltration
-
f(x, t)
discharge
- q0
constant inflow discharge
-
S
f
energy loss gradient or frictional slope
- S0
bed slope
-
t
time
-
u(x, t)
mean velocity along the water depth
-
x
distance
-
Y()
cumulative infiltration
-
(t)
distance separating two flow regions
-
infiltration opportunity time 相似文献
9.
Summary Experiments were conducted in lysimeters (1985) and field plots (1986) to evaluate changes in soil moisture and salinity status following irrigations with different blends of a saline water, SW (ECiw = 6.4 dS/m) and non-saline water, NSW (0.3 dS/m) and their effects on the growth and yield of Mungbean (Vigna radiata L. Wilczek). Normalised to the yield of the treatment receiving NSW (100%), relative seed yields (RY) declined to 73, 11 and 3%, respectively, for the treatments receiving SWNSW blends of 12 (2.5 dS/m), 21 (4.7 dS/m) and SW as such. RY increased to 64 and 74% when NSW was substituted for presowing irrigation and 21 SWNSW blend and SW, respectively were used for postsowing irrigations. Due to moderating effect of rainfall (9.8 cm) during the growing season of 1986, valus of RY obtained with 12 and 21 SWNSW blends were 81 and 42% and increased to 96 and 82% when these waters were applied after presowing irrigation with NSW. Irrigation at presowing with non-saline water leached the salts of shallow depths leading to better germination and initial growth. In addition, plants were able to extract greater amounts of water even from deeper soil layers. The RY of Mungbean was related to the weighted time averaged salinity of the 0–120 cm soil depth (ECe) by RY = 100-20.7 (ECe-1.8). The study indicated that applying NSW for presowing irrigation to Mungbean is more beneficial than using it after blending with saline water. 相似文献
10.
Photosynthesis,leaf conductance,and water relations of cowpea under saline conditions 总被引：1，自引：0，他引：1
Summary Cowpea (Vigna unguiculata L.), grown widely under both irrigated and dryland conditions, is well adapted to drought and high temperature and is moderately salt tolerant. Data on photosynthetic response and regulation of water relations in cowpea under salinity stress is lacking. Therefore, in conjunction with a field plot experiment to establish the leaching requirement of cowpea, measurements were made of carbon dioxide assimilation rates (A) by 14CO2 uptake, leaf conductances to H2O (g1) by tritum uptake, and to CO2 (g), and leaf total water potential (t
1) and osmotic potential (
1).Cowpeas, grown in field plots containing Pachappa fine sandy loam (mixed, thermic, Mollic Haploxeraff), were irrigated daily with saline water (1,350 mg 1–1 total salt concentration) to achieve leaching fractions of 0.17, 0.13, 0.09, 0.07, and 0.02. Cowpea maintained high leaf water potentials, high rates of CO2 assimilation and high leaf conductances under moderately saline conditions (high leaching). Values of t
1 and
1 for high leaching were consistently 50 to 200 J kg–1 higher than for low leaching throughout the day. Calculating
1 at full leaf turgor eliminated diurnal variation in
1. As leaching decreased, however, A, g1, and g, decreased significantly. About 45% of the 1°C assimilated by the leaf was incorporated rapidly into ethanol insoluble compounds. The relationship between A and g1 for cowpea was similar to that reported for other crops.Contribution from the US Salinity Laboratory, USDA-ARS, 4500 Glenwood Dr., Riverside, CA. 92501, USA 相似文献
11.
Relationships between crop temperature,grain yield,evapotranspiration and phenological development in two hybrids of moisture stressed sorghum 总被引：3，自引：0，他引：3
Summary Recent studies have shown that the grain yields of corn (Zea mays L.) and wheat (Triticum aestivum L.) are related to the degree of water stress they undergo. The purpose of the study reported here was to establish relationships between crop temperature and the grain yields, phenological development, evapotranspiration rates (ET) and leaf water potential (
l
) of two hybrids of grain sorghum (Sorghum bicolor L. Moench) subjected to varying levels of plant water stress. The study was conducted at the University of Nebraska Sandhills Agricultural Laboratory in 1978 on a Typic Ustipsamment (Valentine fine sand) soil. The sorghum hybrids used were RS 626 and NB 505. Four irrigation treatments were applied in order to subject the crops to varying levels of water stress during each of three major growth stages. Soil moisture was monitored with a neutron probe. ET was estimated with the water balance technique. Crop temperature was measured with an IR thermometer and leaf water potential was measured with a Scholander pressure bomb. Grain yields were reduced by water stress occuring at anytime during the growing season. Yield reductions were largest when stress occurred during only the grainfill period and were least when stress occurred during the entire growing season. The percentage reduction in sorghum grain yield can be described by an index involving the seasonal accumulation of the daily mid-day temperature differences between well-watered and stressed crops ( TSD). As TSD values increased, ET decreased. However, the correlation of ET with TSD was relatively low (R2 = 0.60) probably due to the limited amount of data available for analysis and inaccuracies in the soil water balance method used to estimate ET. The mid-day temperature of well-watered rows ranged between 18.0 and 32.8 °C with a mid-day temperature range of about 0.5 °C between the well-watered rows in various plots for several days following an irrigation. However, in certain instances, the mid-day temperature range increased to 1–2 °C for a few days before irrigation. This suggests that certain of the rows experienced water stress and should have been irrigated earlier. Yield data support that conclusion. Range in crop temperature within a field appeared to be a sensitive indicator of crop water stress in sorghum. No significant difference in the phenological development of sorghum resulted from water stress except in one NB 505 plot in which plants were stressed throughout the entire season. In that plot, the stressed plants lagged in development behind non-stressed plants by approximately ten days. The differences in mid-day leaf water potentials (
l
) and crop temperatures (T) between stressed and non-stressed vegetation were examined. As T increased up to about 4 °C,
l
, also increased. Beyond that point,
l
decreased while T continued to increase. This behavior was attributed to stomatal closure which permitted an increase in
l
of the stressed plants (hence reducing
l
) even as T continued to increase.Published as Paper No. 6551, Journal Series, Nebraska Agricultural Experiment Station. The work reported was conducted under Regional Research Project 11–33 and Nebraska Agricultural Experiment Station Project 11–50. The work upon which this publication is based was supported in part by funds provided by the Office of Water Research and Technology B-044-NEB, US Department of the Interior, Washington, DC, as authorized by the Water Research and Development Act of 1978. This article was sponsored in part by the Nebraska Water Resources Center, Institute of Agriculture and Natural Resources, University of Nebraska-LincolnResearch Assistant, Associate Professor, Research Assistant, and Associate Professor, University of Nebraska, Lincoln. Contents of this puplication do not necessarily reflect the views and policies of the Office of Water Research and Technology, US Dept. of the Interior, nor does mention of trade names or commercial products constitute their endorsement or recommendation for use by the United States Government 相似文献
12.
Canopy temperature and water stress of cotton crops with complete and partial ground cover 总被引：3，自引：0，他引：3
Summary The use of canopy and air temperature differences to compute a crop water stress index (CWSI) for assessing plant water status was investigated using cotton crop canopies that either fully or partially covered the ground. The complete ground cover canopy condition was studied in a well watered moisture regime in a rainout shelter with measurements made on six Texas cotton race stocks. The partial ground cover canopy situation was investigated in a well watered moisture regime of a commercial cotton variety Paymaster 266 grown in the field. The slope of the nonstressed baseline of the CWSI for a cotton canopy with about 50% ground cover was approximately one-half that reported for full canopies. Values of CWSI calculated with theoretical and empirical procedures agreed more closely under a complete canopy condition than under a partial canopy situation. Values of aerodynamic resistance (r
a
) and canopy resistance for well watered soil moisture conditions (r
ep
)were estimated in order to use the theoretical procedure of computing CWSI. Values of r
a
ranged from 10 to 15 sm–1 and r
cp
from 50 to 60 sm–1. Both the theoretical and empirical procedures showed much promise, but more information is needed to develop techniques for evaluating r
a
and r
cp
under differing canopy and environmental conditions. 相似文献
13.
Summary The paper reports an experimental study of miscible displacement of soluble salts during infiltration and redistribution of water in vertical, homogeneous columns of sandy, sandy loam and clay soils with initially uniform salt and moisture contents. Calcium chloride, mixed uniformly in initially dry and moist soils, was leached with water under transient and steady infiltration conditions. The salt and water profiles were determined immediately following infiltration and after matching total infiltration and redistribution times. Irrespective of different flow conditions and soil types, the centre of mass of salt front coincided with the piston front that would exist given perfect displacement of water initially present in the soil by the water being infiltrated (piston-flow model). Furthermore the advance of centre of mass of salt front was independent of the water application rate and initial soil water content in all soils following both infiltration and redistribution. 相似文献
14.
Summary The onset of water stress within a crop is defined as the time at which the rate of water loss declines below that of a well watered crop in the same locality. The relation to the onset of water stress and soil water status of several readily measured plant parameters was investigated in crops of wheat and soybeans over three years. Evapotranspiration ET was monitored with weighing lysimeters. A noticeable decline in the rate of ET for both wheat and soybeans was detected once 20% to 30% of the total plant available water PAW remained in the 1 m deep lysimeter soil profile. Extension growth of wheat declined when PAW was 33% and 34% in two years of measurement. In soybeans, the decline in the rate of leaf extension coincided with the decline in the rate of ET. Midmorning measurement of exposed leaf water potential L, covered leaf water potential CL and covered plant leaf water potential CP yielded similar results for both wheat and soybeans. Day-to-day variability was least in CP and most in L. Values of CP, L and CL decreased rapidly with PAW < 30%. Daily values of leaf diffusive conductance were variable but there was a general decline in conductance with PAW < 30%. It is suggested that CL may be the easiest and most reliable parameter to monitor as a means of detecting the onset of stress. The results indicated that PAW levels in the root zone of 50% for wheat and 30% for soybean probably do not affect extension growth or plant water status parameters and can thus be used as criteria for irrigation scheduling.Seconded from the Water Research Commission, Pretoria; present address: CSIRO, Division of Irrigation Research, Griffith, N SW 2680, Australia 相似文献
15.
Summary Measurement of leaf water potential (
l
) with a pressure chamber is usually regarded as a reliable and practical field technique. However, recent evidence indicates that results depend on the measurement techniques employed. Field experiments were conducted to identify the magnitude and sources of error affecting pressure chamber measurements of
l
in cotton (Gossypium hirsutum L.) and to develop an accurate and operationally flexible procedure. Water potential of bare cotton leaves was about 0.2 MPa less than aluminum foil wrapped leaves when the elapsed time between excision to chamber pressurization was less than 30 s. The water potential of intact leaves increased 0.3 MPa after 15 s of enclosure in aluminum foil. 5 to 30 min of enclosure were sufficient to reach equilibrium between
l
and water potential within the plant stem. Aluminum foil wrapped leaves maintained their
l
for 2 h stored in a humid, dark box at 21–28 °C while wet wrapped (cheesecloth) or bare leaf
l
increased after one hour because of hydration. An accurate and operationally flexible
l
measurement procedure, suitable for large scale sampling, was defined.Contribution from the USDA-ARS, Water Management Research Laboratory, 2021 S. Peach, Fresno, CA 93727 and the Dept. of Land, Air and Water Resources, University of California, Davis, CA 95616, USA 相似文献
16.
Laboratory experiments were conductedfor determining hydraulic conductivity duringinfiltration in an unsaturated sandy loam soil, usingboth steady state and equilibrium methods. A constanthead Guelph permeameter and a volumetric pressureplate extractor were used. Based on two ponded heightsin the permeameter, the parameters of Gardner'sequation expressing the unsaturated hydraulicconductivity as a function of pressure head (i.e. thesaturated hydraulic conductivity Ks and theexponent ), were estimated simultaneously.Furthermore, it was found that the parameter ,could also be predicted from the soil-water retentioncurve based on equilibrium data obtained from theextractor. This indicated that, for the soil typestudied, one-ponded height in the permeameter methodcould be sufficient for the determination of theexponent , provided that the soil-water retentioncurve is known. 相似文献
17.
This paper presents the development of a practical tool to evaluate the required width of a hydrological buffer zone, in order to maintain the effects of subsurface drainage within reasonable limits. A simple mathematical formulation describing the lateral drawdown extent of a drained water table in unsteady flow conditions was used. Simulation results were worked out by introducing the concepts of protection level or threshold of tolerance for the vegetation of the protected area The latter are expressed in terms of an admissible drawdown combined with exceedance duration and/or frequency criteria. An application of this method to the protection of a peat bog system in the Swiss Jura region is presented. 相似文献
18.
G.A. Cornish 《Irrigation and Drainage Systems》1998,12(3):185-201
The findings of a study of factors influencing the uptake of pressurised irrigation technologies by smallholders in developing countries are presented. The paper reviews the physical and technical characteristics that determine their suitability for use by smallholders. It also identifies a range of pre-conditions relating to water availability, institutional support and economic opportunity that must be satisfied before smallholders will adopt even low-technology pressurised irrigation systems.The review demonstrates that where physical, economic and institutional conditions are right some forms of pressurised modern irrigation technology permit smallholder irrigation of high value crops where surface irrigation would be inappropriate. However, the paper warns against the danger of wide-scale promotion of such technologies without considering the issues of institutional and technical support. Where pressurised systems are promoted to increase water use efficiency it is essential that they be well designed, installed and operated for savings to be realised. 相似文献
19.
The Penman-Monteith model with a variable surface canopy resistance (rcv) was evaluated to estimate hourly and daily crop evapotranspiration (ETc) over a soybean canopy for different soil water status and atmospheric conditions. The hourly values of rcv were computed as a function of environmental variables (air temperature, vapor pressure deficit, net radiation) and a normalized soil water factor (F), which varies between 0 (wilting point, WP) and 1 (field capacity, FC). The performance of the Penman-Monteith model (ETPM) was evaluated using hourly and daily values of ETc obtained from the combined aerodynamic method (ETR). On an hourly basis, the overall standard error of estimate (SEE) and the absolute relative error (ARE) were 0.06 mm h–1 (41 W m–2) and 4.2%, respectively. On a daily basis, the SEE was 0.47 mm day–1 and the ARE was 2.5%. The largest disagreements between ETPM and ETR were observed, on the hourly scale, under the combined influence of windy and dry atmospheric conditions. However, this did not affect daily estimates, since nighttime underestimations cancelled out daytime overestimations. Thus, daily performances of the Penman-Monteith model were good under soil water contents ranging from 0.31 to 0.2 (FC and WP being 0.33 and 0.17, respectively) and LAI ranging from 0.3 to 4.0. For this validation period, calculated values of rcv and F ranged between 44 s m–1 and 551 s m–1 and between 0.19 and 0.88, respectively.Communicated by R. Evans 相似文献
20.
Summary Lysimeters have been frequently used to study crop response to the onset of water stress. To test the representativeness of lysimeter derived criteria for the onset of crop water stress, spring wheat (Triticum aestivum L.) was grown in two field plots with 1.0 m deep lysimeters in the center of each plot. One plot was well-watered while the second was subjected to a drying period with no irrigation. Crop water stress was assessed by monitoring leaf water potential (
l
), stomatal diffusive resistance (r
s
), canopy temperature (CT), evapotranspiration (ET), and soil water content in both plots and lysimeters. The rate of change of all these measured parameters, when compared to the well-watered field control-plot revealed that the field-grown plants showed signs of water stress long before the lysimeter-grown plants. Water stress developed gradually for the field crop, but the transition from the well-watered to the stressed condition happened abruptly for the lysimeter-grown plants. Once this transition occurred, the lysimeter-grown plants were more drought stressed than the field-grown plant. Water profiles measured inside the lysimeter were different from those measured in the adjacent plots. An increase in root length density with depths below 0.6 m was observed in the lysimeters as opposed to a quasimonotonic decrease with depth in the field. The response of the lysimeter-grown plants was a result of the anomalous water content and root distribution. We conclude that threshold values of ET,
l
, r
s
, and CT for the onset of water stress obtained when deep-rooted crops grown in a shallow lysimeter are subjected to drought periods may not be directly applicable to field situations. 相似文献