Actual evapotranspiration and crop coefficients for tropical lowland rice (Oryza sativa L.) in eastern India (original) (raw)
Related papers
Comparison of various methods for estimating reference crop evapotranspiration
The reference crop evapotranspiration (ETo) was estimated for three locations of Bangladesh using the standard Penman-Monteith (P-M) method as recommended by the Food and Agriculture Organization of the United Nations (FAO). The same was also estimated using four other emperical methods and compared with the standard method. The regression equations developed were evaluated with independent data sets. The superiority order were found as: FAO temperature, Radiation, Hargreaves and pan evaporation, respectively. lt is revealed from the study that the regression equation developed herein with FAO temperature method can be used to estimate ETo more accurately than the original FAO temperature method, as well as regression equations with other methods. lntroduction Management practices for optimal utilization of water have been increasingly emphasized because of unevenly distributed rainfall, high evapotranspiration and excessive depletion of groundwater resources. Thus practical methods for the accurate estimation of water use in irrigated agriculture are essential. The estimation of crop water requirement is one of the principal steps in the planning, design and operation of irrigation and water resources systems. Crop water requirements vary with crop characteristics and local condition. Relationships between the evapotranspiration of a pre-selected crop (the reference crop), which is referred to as reference evapotranspiration (ETo), and other crops are established by multiplying ETo by crop coefficients. The ETs depends on local meteorological conditions, whereas the actual evapotranspiration (ET) of a crop depends on its characteristics, time of planting or sowing and stage of crop development.
Journal of Agricultural Science, 2015
This is a review paper on existing methodologies to calculate crop evapotranspiration (ET c ). We have attempted to present all the important ET estimation procedures to date starting from the simple empirical Blaney Criddle method to the complex Shuttleworth model. The common approach to calculate ET c is to estimate a reference crop ET rate (ET ref ) using weather variables from nearby weather station, and multiplying it by an appropriate crop coefficient (K c ). Recently, there have been attempts to calculate actual crop ET (ET a ) directly without using K c . The latter method is still in the developmental phase. This study reviews the existing literature on ET estimation and identifies research needs in the current methods and technology. The extension of the Shuttleworth model for hourly time step and the validity of the Irmak and Mutibwaa model at field level for various crops would be a good milestone for the one step ET estimation. Furthermore, there are indications that the development of a new variable canopy surface resistance (r c ) model, which can be applicable for different crops at different climatic conditions, would be a good contribution in this field.
Agronomy, 2019
Evapotranspiration (ET) is one of the largest components of the water cycle, and accurately measuring and modeling ET is critical for improving and optimizing agricultural water management. However, parameterizing ET in croplands can be challenging due to the wide variety of irrigation strategies and techniques, crop varieties, and management approaches that employ traditional tabular ET and make crop coefficient approaches obsolete. This special issue of Agronomy highlights nine approaches to improve the measurement and modeling of ET across a range of spatial and temporal resolutions and differing environments that address some of the challenges encountered.
Water requirement of irrigated and rainfed crops
International Journal of Hydrology, 2018
Irrigated agriculture has been showing considerable levels of evolution over the last few years, in addition to showing a relevant option for food production. Alternative methods and technologies have been developed for the rational use of water in the field to be used also by small producers, with the aim of increasing productivity in the crops worldwide. It is known that for the proper management of irrigation it is necessary to determine the reference evapotranspiration, ETo. Evapotranspiration consists of a combined process of heat transfer and mass, in the form of vapor, from a vegetated surface to the atmosphere, covering the direct evaporation of soil and plant surfaces and the transpiration of plants. Considering this concept, soon there were difficulties in its use, checking the need for standardization. The ETo is defined as evapotranspiration of a hypothetical crop covering the whole soil, in active growth, without water or nutritional restriction, with a mean height of 0.12m, surface resistance of 70sm-1 and albedo of 0.23. The ETo can be calculated using direct methods: drainage lysimeters, mechanical / electronic weighing, and flotation, field experimental plots method, soil moisture control, "Input-Output" method. Among the various methods for estimating ETo are FAO-24 Radiation, Priestley-Taylor, FAO-24 Blaney-Criddle, Hargreaves-Samani, Camargo-71 and FAO Penman Monteith, standard method considered by FAO. The determination of ETo is a complex nonlinear process, depending on the interaction of several climatological variables, such as air temperature, humidity, wind speed, radiation, as well as the growth stage of the crop. For this reason, several studies with crops of great commercial value, such as corn, tomato, sugarcane, soybean, wheat and cotton, have been developed applying the different methods to determine the ETo, considering different situations.
Water Resources Management, 2011
The study at first recalls the concept of “potential evapotranspiration” (PET), originally considered equal to the evaporation climatic demand; then, it reminds the steps of its progressive evolution toward the concept of “reference crop evapotranspiration” (ET0) determined on irrigated grass. A physical analysis conducted on the evaporation process is subsequently reported to help clarifying the links between ET0 and evaporation climatic demand. This analysis clearly demonstrates that the equivalence of ET0 to evaporation climatic demand is not correct, although still common assumption in recent scientific literature, particularly in hydrology. The study also identifies two processes acting in opposite directions in the dynamics of ET0: (1) the climatic variables determining the evaporation demand, and (2) the canopy resistance which slows down the response of irrigated grass to such demand. The analysis of the respective impact of these two processes on ET0 dynamics shows that the available energy is the dominant process. This variable takes into account the 60–70% of the variation of ET0, both at hourly and daily scales, while canopy resistance only explains 10–20% of ET0 variation of irrigated grass. The study regards different climatic situations. Possible effects on practical applications were also discussed in the conclusions, together with comments on the correct canopy resistance modelling.
2015
Monitoring crop water use has been a topic of interest in the field of irrigation and water resources planning due to increasing competition for fresh water among different users. Irrigated agriculture produces more than 40% of the world's cash and food crops. About two thirds of the world population depends directly or indirectly on it for livelihood [1]. Although irrigated agriculture accounts for 69% of world's freshwater withdrawal, the sector increasingly compete for limited water supplies. Irrigation faces stiff water competition from environmental demands, recreational, municipal, industrial and domestic activities. Thus, continued environmental and regulatory constraints on water supplies are anticipated as the effects of population growth, climate change and declining water conveyance infrastructure continue to evolve. To address these challenges, there is a need to provide new sources of information on crop water use to growers, to enhance their ability to efficiently manage available irrigation water supplies [2]. Crop water use, also known as evapotranspiration (ET), is the water used by a crop for growth and cooling purposes. Evapotranspiration is weather dependent as well as soil, water and plant dependent. It is a process in which the plant extracts water from the soil for tissue building and cooling purposes. Its variability at critical growth stages is important for irrigation scheduling to avoid stressing crops [3, 4]. Nevertheless, ET is one of the most important but difficult water balance element to estimate. Quantifying ET from irrigation projects is vital for water rights management, water resources planning and regulation. Crop evapotranspiration (ET crop) can be estimated using empirical methods [5-7], field measurements [8], and remote sensing techniques [9]. However, the use of empirical methods and field measurements is often sophisticated, expensive, time consuming, and most farmers lack knowledge and skills to apply the techniques [10]. Traditionally ET from agricultural fields has been estimated by multiplying weather based reference ET by crop coefficients (K c) determined according to crop type and crop growth stage. However, there are some concerns with regards to whether the crops grown compare with the conditions represented by the K c values, especially in areas where water is limiting. In addition, it is difficult to predict the correct crop growth stage dates for large populations of crops and fields [3, 7].
Evapotranspiration and crop coefficient for potato in organic farming
Engenharia Agrícola, 2013
The aim of this study was to quantify the water consumption and the crop coefficients (Kc) for the potato (Solanum tuberosum L.), in Seropédica, Rio de Janeiro (RJ), Brazil, under organic management, and to simulate the crop evapotranspiration (ETc) using the Kc obtained in the field and the ones recommended by the Food and Agriculture Organization (FAO). The water consumption was obtained through soil water balance, using TDR probes installed at 0.15m and 0.30m deep. At the different stages of development, the Kc was determined by the ratio of ETc and reference evapotranspiration, obtained by Penman-Monteith FAO 56. The crop coefficients obtained were 0.35, 0.45, 1.29 and 0.63. The accumulated ETc obtained in the field was 109.6 mm, while the ETc accumulated from FAO's Kc were 142.2 and 138mm, respectively, considering the classical values and the values adjusted to the local climatic conditions. The simulation of water consumption based on meteorological data of historical series from 1961 to 2007 provided higher value of ETc when compared with the one obtained in the field. From the meteorological data of historical series, it was observed that the use of Kc recommended by FAO may overestimate the amount of irrigation water by 9%, over the same growing season.
Revista Engenharia na Agricultura - REVENG, 2021
The FAO56 Penman-Monteith model is globally accepted for the accurate determination of reference evapotranspiration (ETo). However, a lack of appropriate data encouraged the improved model’s approach to estimate ETo. This study compared the performance of 10 empirical models of ETo estimation (Penman, Priestley & Taylor, Tanner & Pelton, Makkink, Jensen & Haise, Hargreaves & Samani, Camargo, Benevides & Lopes, Turc, and Linacre) contrasted with the FAO56 model in two regions in Southern Brazil. Data were collected from automatic stations of the Brazilian National Institute of Meteorology (INMET) from December 21, 2019, to February 28, 2021. The determination coefficient (R²), mean square error (nRMSE), mean bias error (MBE), Willmott index (d), and Pearson’s correlation coefficient (r), clustering, and Principal Component Analysis (PCA) were performed. For the different regions, the radiation-based model proposed by Penman was the best alternative for estimating ETo. The model showe...
Calculating crop evapotranspiration using a dual crop coefficient - part 1 : technical
2009
The series of technical articles covers topics related to the planning and design of irrigation systems. In previous articles, we started off by looking at the irrigation planning process, which is aimed at combining climatic, soil, crop, irrigation system and management information in order to identify a suitable irrigation emitter for the system being planned, for an appropriate irrigation cycle length and standing time at the peak irrigation period expected during the growing season of a specific crop. Other topics covered in the second, third and fourth articles of the series, included the calculation of reference evapotranspiration using the Penman-Monteith (PM) equation, the collection of climatic data for the PM equation using weather stations, and the assessment of soils' suitability for irrigation. In the next 3 issues, we look further at the development of crop coefficients to calculate crop water requirements for irrigation planning and management.