Amount Of Evapotranspiration Research Articles

Models of Alfalfa Yield and Evapotranspiration

Data of per-cutting yields and annual yields from four cuttings were collected over six consecutive years for alfalfa grown on three lysimeters. Corresponding evapotranspiration was obtained from weekly water balances. Differences in water management created a range of conditions from water for annual yields of 10 ton/acre (22.4 ko m-²) to 50% yield reductions caused by inadequate soil moisture required to satisfy evapotranspiration demands. Yield and water use efficiency, both annual and per-cutting data, were compared in correlation tests with their corresponding amounts of evapotranspiration. Annual and per-cutting yields were found to be statistically proportional to their evapotranspiration. Annual water use efficiency was not statistically significant with annual evapotranspiration. Although a questionable percentage of the data explained the variance, water use efficiency per cutting and evapotranspiration per cutting had a statistically significant negative correlation.

Estimating Potential Evapotranspiration by the Priestley-Taylor Model

The model of Priestley and Taylor (1972) for evaporation from saturated surface was examined in a radish field. This model contains a parameter (α) corresponding to a multiple of the equilibrium evapotranspiration. Since α is affected by some meteorological factors, it is important to make clear the characteristic of α in relation to these factors. In this paper, the characteristic of α is focused on relativity to the net radiation and the air temperature. The results can be summarized as follows:The amount of evapotranspiration calculated by using daytime meteorological data agreed closely with that measured by the lysimeter. However, the calculation by using 24 hour data was underestimated. It seemed that the underestimation depended greatly on the decreasing net radiation caused by long wave radiation exchange at night time.A seasonal variation of α which was calculated by using measured evapotranspiration and meteorological data was examined. The seasonal variation of α which was calculated by using daytime data cannot be recognized. However, α which was calculated by using 24 hour data increased after around October apparently. This increase in α was due to the rate of decreasing net radiation which was defined by Eq. (4). In case of use of α modified by Eq. (4), even if 24 hour data is used, the calculation is not underestimated.Finally, α in the case of daytime data was modified in connection with air temperature. The results indicated that α was affected very little by air temperature. The use of modified α brought about the rise of accuracy by only 0.8%.

Effectiveness of Straw Mulch for Alleviating Drought Stress of Grain Sorghum

This study was carried out to evaluate the effectiveness of straw mulch to reduce drought stress and to stabilize the productivity of grain sorghum. F1 hybrid variety, E59, was planted on April 20 in four treatments: irrigation-straw mulch, irrigation-no mulch, no irrigation-straw mulch, and no irrigation-no mulch treatments with three replications. Severe water stress occured only during the late grain filling stage because of the unusual delayed end of rainy season this year. Leaf water potentials of grain sorghum measured by pressure chamber during drought stress period were slightly high in mulch treatments, irrespective of soil water conditions by irrigation. Leaf diffusive resistances measured by porometer were high in no mulch treatment of which leaf water potential was lower than in mulch treatment. The amount of evapotranspiration of mulch treatment was lower than no mulch treatment under unirrigated conditions from July 19 to July 30, but there were no differences of evapotranspiration between mulch and no mulch treatments under irrigated conditions. The amount and rate of water consumption to the depth of 40 cm in soil for the same period as above mentioned were less in mulch treatment under unirrigated conditions because of the reduction of evaporation from soil surface. The growth of grain sorghum was not accelerated by mulch under irrigated conditions. However, the growth in mulch treatment was more vigorous under unirrigated conditions. Grain yields harvested on August 20 were high in mulch treat-ment, even if only slightly high under irrigated conditions. From these results, it was concluded that mulch is effective to reduce the adverse effect of water stress by the depression of evapotranspiration and the maintenance of relative high leaf water potential in limited water conditions.

Soil moisture Variations in Upland Field

Thinking of the mechanism of water decrease in upland, the most important problem is thought to be the prediction of soil moisture content in fields by the indirect element such as meteorological factors. In this case, the soil properties and soil conditions must be cleared up as the preceding conditions first of all. Above all, it is necessary to set up the range of available soil moisture for crop productivity.The initial water content in the soil layer was disccused in detail how to be decided under the natural conditions. The author put next a new definition on the field capacity, that is, “Field capacity is the water content at the time when the amount of drainage water in the soil layer just under the available root zone decrease remarkably curing the night after suppling much water or having much precipitation over the holding capacity of soil layer.” In southern Kyushu, we can see these conditions about 48 hours after precipitation for volcanic ash soil. And then, the water content at 48 hours (W48) become nearly constant value in the indication of the degree of water saturation among the soil layers with different porosities. If we use these values, we can find the initial water content of the soil layer by knowing the amount of porosity. For instance, if we take the soil layer 60cm depth, the amount of porosity ∑Po60, and the degree of water saturation SA60 then the initial water content in the 60cm soil layer (WI60) will be expressed as follows, WI60=SA60×∑Po60=0.80×∑Po60(SA60=0.80……observed value)Next, if we analyze the water consumption with the water balance method, we must divide the moisture flux into the upward flow and the downward flow. As to the evapotranspiration, the downward moisture flow must be excepted from the calculation. What is the critical value dividing the flow into the upward or the downward? The author considered of this problem from the standpoint of the environmental evaporation capacity, which is calculated as the latent heat flux in the heat balance equation. Judging by the comparison, the critical value is thought to be the value of pF1.6, and that corresponds to the 48 hours water content (≅field capacity) for volcanic ash sandy loam in southern Kyushu.We examined the relationships among the estimated amount of evapotranspiration from the heat balance method (lEo/l), those from the net radiation (S/l), tne' observed evaporation with 20cm pan evaporimeter (Ew) and the observed evapotranspiration from the soil layer of 0-50cm by the water balance method (pET). As the results of these comparisons, the relationships, pET=lEo/l=EW……(W≥W.c.)were found out in our experimental fields throughout the duration from July to November.The water content in the soil layer of 50cm (W50) is obtained from, W50=SA×∑Po50-WW50-pET·t……(W≥W.c.)W50=(SA×∑Po50-WW50)·exp(-W/W.c.×pET·t)…(W<W.c.)where, t: elapsed days from the 2 days after rain or irrigation, W: available water content, WW: unavailable water content, nearly equall to the wilting point, PET: potential evapotranspiration, ∑Po: porosity.When it is little rain on the way of drying process, we can compensate the soil moisture content adding the amount of rain to the right side of the above mentioned equations. Besides, for indirect prediction, we had better use the accumulated amount of observed values day by day such as

MECHANISM OF UNCONFINED GROUND WATER RECHARGE AT HAKUSAN ON THE KONGÔ TERRACE, TÔKYÔ

In this paper the author analyzes the mechanism of natural recharge of unconfined ground water at Hakusan on the Hongô terrace in Tôkyô putting emphasis on water balance. Special attention is paid to variations in soil moisture, whose amount has not exactly been observed though the important role of it in the hydrologic cycle is widely accepted. As a result of this study some characteristics are found concerning the mechanism of unconfined ground water recharge in urban area and redistribution of soil moisture in the Kantô Loam formations. The Hongô terrace, whose top is about 25m above sea level, is a Pleistocene upland (M 2), and is located in the eastern margin of the Musashino upland. This terrace consists of the volcanic ash called Kantô Loam (6 to 7m thick), Yamanote sand and gravel (4 to 5m thick, but its upper part of 1 to 2m in thickness is clay), and the sand stratum of Upper Tôkyô formation (more than 5m thick) in the descending order. The main uncon-fined aquifers of ground water studied are the Yamanote gravel bed and the sand stratum of Upper Tôkyô formation. Annual variation of ground water level in the aquifer is within the range of 6m to 12m below the surface. The studied area is located in an ordinary residen-tial area and the experimental garden (Tôkyô University Botanical Garden) is nearby. From April in 1962 to March in 1968 ground water level in the unconfined aquifer was measured daily in an observation well at Hakusan. At that place, the fluctuations of ground water level is affected by rainfall. Relation between rainfall and ground water level was in-vestigated, and the rise and fall of round water level in one period was found to be deter-mined by the total rainfall bserved in a 6-month period before that time. Contribution of the rainfall about 1 to 2 months before is the most prominent. However, the individual rises of ground water level correspond to individual rainfalls observed in the preceding 10 days. At Hakusan, hydrologic elements such as rainfall, fluctuations of soil moisture, the outflow of ground water and artificial recharge to the main aquifer were observed for one year from April in 1967 to March in 1968. Water balance analysis was applied and the relationship between the annual march of these water balance factors and that of ground water level was investigated.As for the annual total of water balance factors, about 1000mm of annual rainfall can be divided into following entries : the surface runoff is about 210mm, the amount of evapo-transpiration about 500mm, effective rainfall (amount of rainfall that is available for ground water recharge) for ground water recharge 290mm, of which 280mm is actually added to ground water storage. In addition to this, a 410mm of artificial recharge from leakage of waterworks pipelines is added and the total ground water recharge to the aquifer is 690 mm. The discharge from ground water reservoir is 670mm. It is worthy of note that unconfined ground water in urban area is balanced by a large quantity of artificial recharge (leakage from pipelines). The amount of evapotranspiration at Hakusan is about 50 to 60 percent of its average value in the Kanto Plain, which was calculated by the method of heat budget. Soil moisture measurement from the surface to the depth of 15m was made by a neutron soil moisture meter. The seasonal variation of soil moisture is large in a layer from the surface to 8m (Kantô Loam formation and Yamanote Clay bed), and the difference between the maximum in summer and the minimum in spring is more than 100mm. It is recognized that soil moisture changes greatly and it moves upward in the lower part of Kanto Loam formation, in which little variation of soil moisture was believed to exist, though existence of slow downward movement of soil moisture was reported.

Water Yield Changes after Converting a Forested Catchment to Grass

A 22‐acre catchment in the southern Appalachians was cleared of hardwood forest in 1958 and 1959 and seeded to Kentucky 31 fescue grass in 1959 and 1960. The amount of evapotranspiration by the grass cover was closely related to the amount of grass produced. During years when grass production was high, water yield from the catchment was about the same as or less than the expected yield from the original forest. As grass productivity declined, water yield gradually increased until it exceeded the predicted yield from the forest by over 5 inches annually. The grass appeared to evaporate more water early in the spring and less water late in the summer than the original forest cover.

The evapotranspiration component of a pastoral experimental catchment

The amount of evapotranspiration occurring from a pastoral catchment was determined by an assessment of the hydrologic balance within the catchment. A measure of the variable for changes in water content was achieved by the evaluation of soil store deficits antecedent to runoff events. Thus, the intervals of time for the determination of the amounts of evapotranspiration were confined to periods between runoff events. For those intervals when the index of topsoil moisture stress did not exceed a pF value of 3.5, a ratio of one existed between measured evapotranspiration and the index of potential evapotranspiration. With the use of this ratio in conjunction with the soil moisture record, variations in rates of evapotranspiration were presented for the years 1963 to 1966. Such data indicated that the prevailing land-use was inefficient in its consumption of water.

Studies on the characteristic features of water consumption in various crops. IV

In order to make clear the characteristics of water consumption of taro plants under upland field conditions, the authors measured both leaf transpiration and evaporation from the soil surface using the chamber method (the vopor-trnsfer method).The measurements were carried out at Taketoyo, Aichi in summer of 1963, 1964 and 1966.1. The amounts of transpiration of taro plants during the growth periods (from late May to early October) were 370mm and 408mm in 1963 and 1964, respectively. For the sameperiod in 1966, the evapotranspiration amount of these plants was 582mm.2. Transpiration rate of taro plants in the early growth stage was little owing to small leaf area, on the other hand the rate of evaporation from the soil surface was much on account of slight covering the soil surface with the foliage of taro plants.The rate of transpiration increased gradually with the increase of leaf area and the rise of air temperature. The maximum transpiration observed was 6.8mm/day on September 10, 1964.About 60% of total amounts of transpiration was transpired for 50 days from July 24 to September 10, 1964. The water requirements were relatively larger (500-800g/g) in the early and late growth stages than the middle growth stage (200-300g/g).3. The relative transpiration increased gradually with the progress of growth, nemely, the increase of leaf area index. This relationship is approximately expressed with the rectangular hyperbolic equation:RT=bL/(1+aL)where RT=relative transpiration, i.e. the value of the rate of transpiration (mm/day) divided by the pan-evaporation (mm/day); L=leaf area index; a and b=constants. The value of inflection point of the hyperbolic curve was about 2.5 of leaf area index, which corresponded to the stage that the soil surface was covered almost thoroughly with the foliage of taro plants.4. Unit relative transpiration, namely, the rate of transpiration (g dm-2 12 hrs-1) divided by the pan-evaporation (mm 12 hrs-1) or daylight hours mean saturation deficit (mm Hg), decreased exponentially with increasing leaf area index. It was approximetely applicable to the above relation that the exponential eqution was given byTp=Tp0e-KLwhere Tp=transpiration power, i.e. unit relative transpiration; Tp0=hypothetical transpiration power when leaf area index was zero; e=base of natural logarithm; L=leaf area index; K=constant.5. The rate of evaporation from the soil surface varied by the covering degrees of the soil surface with the foliage of taro plants.The ratio of the evaporation from the siol surface to the evapotranspiration was about 30% in the stage of largest leaf area index (4.0).6. The largest evapotranspiration rate of taro plants was 9.8mm/day in summer. The daily mean evapotranspiration rate of taro plants was within the range of 5-7mm/day in summer, at Taketoyo, which was estimated by relative evpotranspiration was 1.12-1.14.7. As regards correlations among transpiration, evapotranspiration and various environmental factors, in general transpiration had a positive correlation with leaf area and evapotranspiration had positive correlations with pan-evaporation or solar radiation.

Advective influences on the reduction of evapotranspiration in a coastal environment

Incoming air from an ocean may either supply heat to a land area or serve as an energy sink. A marked example of the energy sink phenomenon occurs in a coastal valley of California. Advective cooling resulted in much lower evapotranspiration than amounts reported for interior locations during the two months studied, July and September. Evapotranspiration from irrigated ryegrass was equivalent to about 2/3 of net radiation on clear days. This ratio is lower than the 8/10 or 9/10 commonly observed in humid interior areas and is much lower than amounts reported for interior desert conditions. Overcast days having low net radiation did not produce amounts of evapotranspiration that were proportionally as low. This observation indicated that there was a trade off beween radiation and advection under these coastal conditions where a critical balance existed between air and surface temperatures.

Climatology of Drought at Kagawa Prefecture

From the view-point of the protection of drought damage, it is essential to study the water balance, namely, we must investigate not only the amount of precipitation but also the rate of evapo-transpiration and soil moisture storage, water surplus and water deficient. Drought damage of field crops depends upon the soil moisture storage and water deficient of the fields. Fig. 1 shows the seasonal change of soil moisture storage and water deficient, estimated by adopting the conception of potential evapo-transpiration, at Takamatsu (1955-1964).Paddy rice fields of Kgawa Prefecture are cultured under the highly arranged irrigation system of reservoirs. So, in this prefecture, we must investigate the water balance, especialy the amount of evapo-transpiration and precipitation in the irrigation period and the water surplus in the non-irrigation period. Tables 1-4 show the results of water balance at Tadotsu (1893-1964), and their influence upon drought damage. Fig. 2 shows the water balance in Kagawa Prefecture (12 weather stations, 1955-1964).

Studies on the Evapo-transpiration from the Paddy Field in the Cooler Regions (1)

This paper deals with the results of measurement of evapotranspiration from the paddy fieild at Kuroishi City situated in the cooler region of Japan, from 1953 to 1956.The amounts of transpiration were below 1mm/day in the early growth stage of rice plants and increased gradually with their growth (Fig. 1). But, the amount of evaporation decreased with their growth (Fig. 6).The evapo-transpiration rates to the evaporation E obtained from the meteorological observation field lay within about 1.0-1.3 in the early growth stage and increased after the young ear formation stage. But the rates decreased again from about the tenth day after heading (Fig. 7).Two peaks of the transpiration rates to E were found after the young ear formation stage and the heading stage. From the index of growth amount ln (l and n mean respectively the plant length and the number of stems per unit area), the transpiration rate t/E (t means the amounts of transpiration) and the seasonal changes of τ(τ means t/E/ln×104), it was presumed that two peaks for t/E during irrigation period would probably be found for the case of ln.Total evapo-transpiration amounts throughout the irrigation period varied annualy from 440mm to 553mm and were 493mm on the average, showing 1.22 times as much as E. The average transpiration amount was found to be 0.45 times as much as the evapo-transpiration. The annual changes for the average transpiration amount were larger than the cases of the evaporation amounts obtained from the paddy field.

Studies on the Methoed for Measuring Amounts of Evapotranspiration : 1. A method by measuring humidity using transpiration chambers

Studies on the Methoed for Measuring Amounts of Evapotranspiration : 1. A method by measuring humidity using transpiration chambers

Interception losses in grassy vegetation

Studies of the interception process in grassy species are reported for a series of laboratory tests. Procedures, equipment, and techniques were developed to determine the magnitudes of rainfall interception on grasses and to measure the resultant losses. It was found in vigorously growing grass plots that the evaporation of a given amount of intercepted moisture was accompanied by a like reduction in the amount of evapotranspiration from the plants. Total moisture use was approximately the same in plots with wet and dry leaf surfaces. The interception storage component and precipitation passing through the vegetative canopy as combined stemflow, throughfall and drip (STD) were measured to determine the relationships and magnitudes. Storage capacities were observed to agree essentially with those reported by other investigators although some variations can occur with different storm types and intensities. Values of STD were found to be quite significant even at the beginning of small storms.

The Association between Free‐Water Evaporation and Evapotranspiration of Spring Wheat Under the Prevailing Climatic Conditions of the Plains Area of Montana

AbstractIn a study involving over 25 years of crop and weather data at 2 stations in the Northern Plains of Montana, evapotranspiration of dryland spring wheat was negatively correlated with free‐water evaporation. In years of high temperatures and low rainfall, i.e., high free‐water evaporation, reduced crop growth and an inadequate supply of soil moisture resulted in low evapotranspiration.Cultural practice and geographic location influenced the amount of evapotranspiration per unit of free‐water evaporation. A greater amount of evapotranspiration per inch of free‐water evaporation always resulted under fallow than under continuous wheat.When adjustments were made for variation in size of plants (evapotranspiration/total dry weight ratio), the correlation between free‐water evaporation and evapotranspiration per unit of dry matter produced was positive. However, the degree of association between free‐water evaporation and the evapotranspiration ratio was apparently reduced by limited soil moisture supply.The effects of cultural practice, geographic location, and limited moisture supplies on the magnitude of evapotranspiration per unit of free‐water evaporation detract considerably from the value of free‐water evaporation measurements as an indication of water use by wheat plants under semiarid conditions.

Geographical Distribution of Actual Evaporation from Extensive Land Areas in Japan

According to the THORNTHWAITE's idea. on the potential evapotranspiration, it has been calculated total amounts of actual evaporation and transpiration from extensive land areas on various localities in Japan. Distribution of annual amounts is shown in the Fig. 1. From this figure, we can see that regions where evaporate and transpire more than 850mm annually, are found on the South Seaside. And isopleth of 800mm runs across the Honshu nearly along the Parallel of 35 N. Amounts of the Sanin nd the Kwanto Basin are 750-800mm, and those of the Central Highland and the Tohoku are less than 700mm. If we compare these amounts with those of ordinal evaporation which are measured by atomometer at weather stations, ratios of actual to observed evaporation become mostly about 60-70%, and regional differences in this ratio can not be clearly distinguished each other. Frequencies of the ratios in each class are shown in the Tab. 1. Seasonal variation of the evapotranspiration is fairly systematic. The maximum amounts occur in summer and the minimum can be seen in winter in general., as is shown in the Tab. 2. Geographical distribution of the evapotranspiration at various months are shown in the Figs. 2-4. Fig. 2 indicates the January situation. The larger amounts of this month are only about 10mm which are observed at the South Seaside region. Various places in Central Highland. and the Tohoku District present very` little amounts less than 0mm. The same pattern of distribution can be seen also October-April. Fig. 3 shows the situation of May. Fig. 4. shows the July situation. This is the summer type of distribution. The absolute values of evapotranspiration amounts are very large. We can observe more than 100mm almost all places. The larger amounts more than 160mm can be observed at the Kuyushu and the Setouchi Districts. Then monthly ratios of the actual evaporation at several. places are shown in the Tab. 3. In winter their ratios are very small, but in summer they become very large. And the maximum values, of this ratios mostly observe in July or September. In these months on some localities, amounts of evaporation from extensive land areas (calculated) exceed those of evaporation from water surface being measuered by a atom-ometer.