Actual Crop Coefficient Research Articles

Upgrading Maize Cultivation in Bosnia and Herzegovina from Rainfed to Irrigated Systems: Use of Remote Sensing Data and the Dual Crop Coefficient Approach to Estimate Evapotranspiration

A two-year experiment was conducted with a local maize hybrid under full (F) and deficit (D) drip irrigation and rainfed conditions (R) to estimate maize evapotranspiration in Bosnia and Herzegovina (BiH). Three approaches, namely, A&P, SIMDualKc (SD), and vegetation index (VI), to estimate the actual crop coefficient (Kc act), the actual basal crop coefficient (Kcb act), and the actual crop evapotranspiration (ETc act), were applied with the dual crop coefficient method and remote sensing (RS) data for the first time. While Kcb act from all approaches matched FAO56 tabulated values, SD showed differences in comparison to A&P of up to 0.24 in D and R conditions, especially in the initial and mid-season stages. VI demonstrated very good performance in all treatments. In F, the obtained Kc act for all approaches during the initial and end stages were higher than the tabulated values, ranging from 0.71 to 0.87 for the Kc ini act and from 0.80 to 1.06 for the Kc end act, while the mid-season period showed very good agreement with the literature. The maize crop evapotranspiration range is 769–813 mm, 480–752 mm, and 332–618 mm for F, D, and R, respectively. The results confirmed the suitability of both approaches (SD and VI) to estimate maize crop evapotranspiration under F, with the VI approach demonstrating an advantage in calculating Kcb act, Kc act, and ETc act values under water stress conditions. The higher observed yields (67.6%) under irrigation conditions emphasize the need to transition from rainfed to irrigation-dependent agriculture in BiH, even for drought-resistant crops like maize.

Evapotranspiration and Crop Coefficient of Sorghum (Sorghum bicolor L.) at Melkassa Farmland, Semi-Arid Area of Ethiopia

Sorghum has an enormous role in the economy of sorghum-growing nations. Supplying a precise amount of water to a crop based on crop needs is the main agenda in implementing water-saving agriculture. Non-weighing type lysimeters were used to determine actual crop evapotranspiration and crop coefficient of sorghum at the experimental farm of Melkassa Agricultural Research Center situated in the semi-arid area of Ethiopia. Soil-water balance approaches were applied to obtain actual crop evapotranspiration, while the Penman-Monteith technique was used to determine reference evapotranspiration. Growth stages-wise crop coefficient was computed as a ratio of actual crop evapotranspiration to reference evapotranspiration. The total seasonal sorghum actual crop evapotranspiration during the 2017 and 2018 experimental years was 358.6 and 377.54 mm, respectively. The 2 years average sorghum actual crop evapotranspiration was 368.07 mm. The mean locally developed actual crop coefficient values of 0.55, 1.15, and 0.59 were observed for the initial, mid, and end-season, respectively. The FAO-adjusted crop coefficient values for mid and end-season were 1.01 and 0.52, respectively. The developed Kc values considerably differed from the FAO-adjusted Kc values. So, the determination of actual crop evapotranspiration and crop coefficient for crop growth at local climate conditions is vital for decision-making concerning water management in the area where irrigation is practiced.

The Potential of Hydroponic Kit-Based Growing on a Self-Fertigation System for Pagoda Mustard (Brassica narinosa L) Production.

Agricultural land has been converted into settlements following the population growth in various parts of the country. The productivity of horticulture, particularly pagoda mustard (Brassica narinosa L), decreases with the narrowing of fields. The main milestone as a promising solution to overcoming this issue is applying the hydroponic technique. This study aims to analyze the potential of hydroponic kit-based growing on a self-fertigation system for pagoda mustard production. In contrast to general hydroponic, the proposed hydroponic kit is supported by a smart valve component as a unique novelty used for the automatic distribution of nutrients without electrical power (zero energy). The mustard seeds were sown on rockwool for two to three days in a dark room and placed in the sun for seventeen days. A total of 50 pagoda mustard seeds were arranged evenly on a self-fertigation system tray following a zig-zag planting pattern for forty days. The seed has the following morphological characteristics: average height of 22.88 cm, biomass width of 26.42 cm, root length of 23.4 cm, and weight of 241.5 g. Furthermore, the production requires a total fertigation consumption of 186 L (equal to 0.0935 L/plant day-1) with an actual crop coefficient between 0.01 and 0.54. The proposed system shows good performance for mustard growth with a uniformity value between 80 and 89%. Finally, hydroponic kit-based growing on a self-fertigation system can be applied in various areas to produce and maintain a sustainable food supply.

Leveraging remotely-sensed vegetation indices to evaluate crop coefficients and actual irrigation requirements in the water-stressed Maipo River Basin of Central Chile

Assessment of irrigation needs for agricultural production has commonly relied on reference crop coefficients derived using limited climatic conditions. This work focused on evaluating actual crop coefficients (Kc) by leveraging available satellite data from Landsat 8 Operational Land Imager (OLI) and Terra Moderate Resolution Imaging Spectroradiometer (MODIS). This method built on the linear relationship and variability between reference Kc from the Food and Agricultural Organization (FAO) and specific site response in Normalized Difference Vegetation Index (NDVI). A regional model was developed for the water-stressed Maipo River Basin of Central Chile during the growing seasons of maize from 2018 to 2022. Throughout model validation, NDVI-based Kc predictions of high quality were found with R-squared scores ranging from 0.77 to 0.97. Relying on Earth observations, this approach provided site-specific Kc values and estimates of actual evapotranspiration without requiring site instruments and/or particular knowledge of farming schedules. Overall, this study has the potential to assist individuals and organizations around the world in improving irrigation management approaches, and advance precision agriculture in the context of water scarcity.

Assessing Spatio-Temporal Dynamics of Deep Percolation Using Crop Evapotranspiration Derived from Earth Observations through Google Earth Engine

Excess irrigation may result in deep percolation and nitrate transport to groundwater. Furthermore, under Mediterranean climate conditions, heavy winter rains often result in high deep percolation, requiring the separate identification of the two sources of deep percolated water. An integrated methodology was developed to estimate the spatio-temporal dynamics of deep percolation, with the actual crop evapotranspiration (ETc act) being derived from satellite images data and processed on the Google Earth Engine (GEE) platform. GEE allowed to extract time series of vegetation indices derived from Sentinel-2 enabling to define the actual crop coefficient (Kc act) curves based on the observed lengths of crop growth stages. The crop growth stage lengths were then used to feed the soil water balance model ISAREG, and the standard Kc values were derived from the literature; thus, allowing the estimation of irrigation water requirements and deep drainage for independent Homogeneous Units of Analysis (HUA) at the Irrigation Scheme. The HUA are defined according to crop, soil type, and irrigation system. The ISAREG model was previously validated for diverse crops at plot level showing a good accuracy using soil water measurements and farmers’ irrigation calendars. Results show that during the crop season, irrigation caused 11 ± 3% of the total deep percolation. When the hotspots associated with the irrigation events corresponded to soils with low suitability for irrigation, the cultivated crop had no influence. However, maize and spring vegetables stood out when the hotspots corresponded to soils with high suitability for irrigation. On average, during the off-season period, deep percolation averaged 54 ± 6% of the annual precipitation. The spatial aggregation into the Irrigation Scheme scale provided a method for earth-observation-based accounting of the irrigation water requirements, with interest for the water user’s association manager, and at the same time for the detection of water losses by deep percolation and of hotspots within the irrigation scheme.

Crop coefficients and water use of young almond orchards

An observational study was conducted in the northern Sacramento Valley in California, United States to determine crop water use and crop coefficients of three adjacent young Nonpareil/Monterey almond orchards. Methods used to quantify evapotranspiration estimates of crop water use include (1) a soil water balance and (2) a land surface energy balance using eddy covariance. Three adjacent almond orchards that were planted in 2016, 2017, and 2018 were monitored from 2018 to 2020. Actual crop coefficients were determined using actual evapotranspiration estimates from each orchard and short grass reference evapotranspiration from the Gerber South California Irrigation Management Information System station. Results showed that crop water use and crop coefficients increased until the 4th year, indicating the need to closely consider tree development and orchard age as factors in irrigation scheduling of young almond trees. The results led to the conclusion that farmers should use development or age-specific crop coefficients in developing orchards for irrigation scheduling until the 4th year when they can start using mature almond crop coefficients. The mid-season actual crop coefficients were 0.35, 0.55, 0.88, 1.04, and 0.99 for 1-, 2-, 3-, 4-, and 5-year-old almond orchards. This study has generated baseline data on crop water requirements of young almond orchards that could be useful for (1) developing irrigation scheduling tools for young almond orchards, and (2) determining water budgets for areas with new almond orchards.

Performance of Three Different Native Plant Mixtures for Extensive Green Roofs in a Humid Subtropical Climate Context

Most of the services and benefits of green roofs are related to the substrate as well as the vegetation layer. Although plant selection should be made on the basis of green roof typology, morphology, and climate conditions, very often, Sedum species only are used worldwide. However, they do not always guarantee the best performances; hence, it is important to investigate different plant species and their performance in different climate contexts. Herein, an experiment was conducted using three plant mixes (i.e., a Sedum mix, a perennial herbaceous mix, and a suffruticose mix), grown in boxes containing two substrates (a volcanic substrate or a recycled crushed brick substrate) and two drainage/storage layers (a preformed layer or a mineral layer), in factorial combination. The Sedum mix showed a high canopy cover, comparable to or even higher than that of the other mixes, particularly when supplemental irrigation was stopped. However, the actual crop coefficient (Kcact) of the herbaceous and suffruticose mixes was often higher than that of the Sedum mix. The results also showed that both the substrate and the drainage/storage layer may improve Kcact values as a consequence of their capacity for stormwater retention.

Estimating of Wheat Water Requirement Using Remote Sensing at El-Menia Governorate Desert Fringe-Egypt

In hyper-arid and arid zones, the crop water requirement management is considered the vital component for sustaining the crop production particularly under drought condition. As such, further investigation is needed to determine optimal water requirements to avoid wasting water in zones already facing water shortages.Further, estimating reference Evapotranspiration(ET0)and Crop Coefficient(Kc)is fundamental requirement of agricultural water management. Thus, the aim of this study is determining an actual crop coefficient(Kc)for winter wheat using remote sensing tools [Normalized Difference Vegetation Index(NDVI)and Soil-Adjusted Vegetation Index(SAVI)] - obtained from Sentinel-2A satellite images, as well as the influence of Accumulated Growing Degree Days(AGDD)for wheat on NDVI and SAVI. Consequently,data were obtained during winter wheat season(November 2019 - April 2020)on El-Menia Governorate Desert Fringe.Data analysis indicated that the total amount of AGDD required to obtain was 1408.37 C°/season for wheat to develop in its life cycle. Moreover, SAVI value recorded the highest value(0.77)in January when the NDVI obtained 0.53 at the same period. Values of NDVI increased dynamically and acquired was 0.53 which was the highest value after wheat obtained 863.79 C°/days(heat unit)in January. Furthermore, there is a linear relation between NDVI and actual Kc which reflect a strong correlation between them for all of the growing stage. Finally, the actual water requirement was 2532.68 m3/fed/season, which is a less than value (2791 m3/fed/season)calculated FAO method. Actual crop coefficients[Kc (actual)]estimated from remote sensing(RS)using NDVI, SAVI with the AGDD equation is beneficial for irrigation scheduling, evaluation of irrigation, water use efficiency and project performance and agricultural water budgets.

Validation of Crop Coefficients and Water Requirement of Maize Crop in the Temperate Climatic Region of India

The field study was conducted on Lysimeter by employing the soil water balance method to compute the water requirement and Crop coefficient of Maize in the temperate climatic zone of India. Non-weighing type lysimeters (drainage type) of 2 × 1.5 × 2 m was installed to compute the irrigation requirement, actual crop evapotranspiration (ETc) and actual crop coefficient of maize by water balance method. The water requirement of maize was found 410.4 mm using lysimeter data. The mean daily reference evapotranspiration (ETo) of maize ranged from 0.91 mm/day in the starting growth period to 5.29 mm/day at midseason. The peak ETo of Maize was found 6.3mm/day. The computed crop coefficient (Kc) values of Maize for diffrent crop growth stages were 0.53 for intial, 0.93 for development , 1.05 for mid-season, and 0.78 for late season .A Correlation was also established between Penman-Monteith (P-M) and four other reference Evapotranspiration methods.

Application of Dual Crop Coefficient Approach for Estimation of Crop Water Requirement for Summer Sesame using SIMDualKc Model

Dual crop coefficient approach was used to estimate the crop water requirement of summer sesame in South Gujarat Agro-climatic Zone of Gujarat state. Field experiment was conducted with drip and border irrigation systems during summer season of 2018 and 2019. Basal crop coefficient and soil evaporation coefficient were separately estimated using FAO-56 method and SIMDualKc model. The SIMDualKc model, validated using observed available soil water content (ASW), performed well for both systems (R2 = 0.76-0.85, NSE= 0.75-0.94, RMSE= 0.25- 0.50). FAO-56 estimated Kc values for initial-, mid-, development- and late-stages of drip irrigated summer sesame (0.69, 0.90, 1.04, 0.65) were lower than those for border irrigated crop (0.72, 0.98, 1.05, 0.74). Under drip irrigation system, the SIMDualKc model estimated comparatively lower values of Kc only for initial and late stages of crop growth (0.39, 0.44). Crop coefficients derived using SIMDualKc model estimated lower water requirements during initial and end stage, while FAO method estimated lower water requirement during development and mid-stage. Scheduling of drip irrigation using FAO-56 and SIMDuelKc estimated crop coefficients led to average water saving of 7.6 % and 18.0 % over border system. The SIMDualKc model-based Kc values are recommended for estimating daily actual crop coefficients and crop water requirements of summer sesame crop cultivated in the South Gujarat region.

A Decade of Unmanned Aerial Systems in Irrigated Agriculture in the Western U.S.

Highlights Unmanned aerial systems (UAS) are able to provide data for precision irrigation management. Improvements are needed regarding UAS platforms, sensors, processing software, and regulations. Integration of multi-scale imagery into scientific irrigation scheduling tools are needed for technology adoption. Abstract . Several research institutes, laboratories, academic programs, and service companies around the United States have been developing programs to utilize small unmanned aerial systems (sUAS) as an instrument to improve the efficiency of in-field water and agronomical management. This article describes a decade of efforts on research and development efforts focused on UAS technologies and methodologies developed for irrigation management, including the evolution of aircraft and sensors in contrast to data from satellites. Federal Aviation Administration (FAA) regulations for UAS operation in agriculture have been synthesized along with proposed modifications to enhance UAS contributions to irrigated agriculture. Although it is feasible to use sUAS technology to produce maps of actual crop coefficients, actual crop evapotranspiration, and soil water deficits, for irrigation management, the technology and regulations need to evolve further to facilitate a successful wide adoption and application. Improvements and standards are needed in terms of cameras’ spectral (bands) ranges, radiometric resolutions and associated calibrations, fuel/power technology for longer missions, better imagery processing software, and easier FAA approval of higher altitudes flight missions among other issues. Furthermore, the sUAS technology would play a larger role in irrigated agriculture when integrating multi-scale data (sUAS, ground-based or proximal, satellite) and soil water sensors is addressed, including the need for advances on processing large amounts of data from multiple and different sources, and integration into scientific irrigation scheduling (SIS) systems for convenience of decision making. Desirable technological innovations, and features of the next generation of UAS platforms, sensors, software, and methods for irrigated agriculture, are discussed. Keywords: Agricultural water management, Irrigation prescription mapping, Irrigation scheduling, Precision irrigation, Remote sensing, Sensors, Spatial crop evaOotranspiration, Unmanned aerial systems.

Application of Dual Crop Coefficient Approach for Estimation of Crop Water Requirement for Summer Sesame using SIMDualKc Model

Dual crop coefficient approach was used to estimate the crop water requirement of summer sesame in South Gujarat Agro-climatic Zone of Gujarat state. Field experiment was conducted with drip and border irrigation systems during summer season of 2018 and 2019. Basal crop coefficient and soil evaporation coefficient were separately estimated using FAO-56 method and SIMDualKc model. The SIMDualKc model, validated using observed available soil water content (ASW), performed well for both systems (R2 = 0.76-0.85, NSE= 0.75-0.94, RMSE= 0.25- 0.50). FAO-56 estimated Kc values for initial-, mid-, development- and late-stages of drip irrigated summer sesame (0.69, 0.90, 1.04, 0.65) were lower than those for border irrigated crop (0.72, 0.98, 1.05, 0.74). Under drip irrigation system, the SIMDualKc model estimated comparatively lower values of Kc only for initial and late stages of crop growth (0.39, 0.44). Crop coefficients derived using SIMDualKc model estimated lower water requirements during initial and end stage, while FAO method estimated lower water requirement during development and mid-stage. Scheduling of drip irrigation using FAO-56 and SIMDuelKc estimated crop coefficients led to average water saving of 7.6 % and 18.0 % over border system. The SIMDualKc model-based Kc values are recommended for estimating daily actual crop coefficients and crop water requirements of summer sesame crop cultivated in the South Gujarat region.

Determination of crop water use and coefficient in drip-irrigated cotton fields in arid regions

A 3-year field experiment was conducted in Aksu region in Northwest China to determine crop water use, suitable irrigation mode and actual crop coefficient (Kc) in drip-irrigated cotton fields. In the experiment, 12 non-weighing large lysimeters were used to measure cotton water use under various irrigation modes. Then a micro-lysimeter was placed in each large lysimeter to monitor soil evaporation (E). Adjustments were done for a number of factors (including irrigation, meteorology, plastic mulching, water stress and salinity stress) in order to compare FAO-adjusted Kc (Kc-FAO) with the local actual Kc (Kc-loc). The results showed that: 1) plastic mulching with 0.6 cover ratio and 37.5 mm drip irrigation quota gave a crop water requirement of 536.4 mm; which was suitable for the study area. Also Kc-loc were respectively 0.28, 0.97 and 0.31 for early, middle and late growth stages. 2) Kc-FAO generally reflected the trend in Kc-loc for the entire growing season. The suggested 0.1 adjusted coefficient under plastic mulching for the initial growth stage was relatively low, and was most rational for the study area when increased to 0.25. 3) E/ET ratio was low (19.1–24.5%) under mulching treatment and relatively high (27.7–32.7%) under non-mulching treatment. 4) While change in E/ETo ratio was linear or logarithmic, that in T/ETo ratio was a power function of the canopy cover. Also the two rates responded to the interaction effects of canopy cover and soil water content. The results could lay the basis for developing scientific, data-driven water-saving strategies in the study area and elsewhere.

Water Use Efficiency, Yield and Crop Coefficient (Kc) of Groundnut crop under different Water Regimes

The pot experiment was carried out during September 2015 to January 2016 at instructional farm, College of Agricultural Engineering, UAS Raichur under rain shelter to study the effect of different water regimes, (i.e. T1:100, T2:90, T3:80, T4:70, T5:60 and T6:50) per cent of water application with available moisture holding capacity on grain yield and water use efficiency. Completely Randomized block design with four replications was used in this study. The results showed that there was significant difference between the yield and (WUE) under different levels of irrigation. The total irrigation water applied were (i.e., 211.98, 243.02, 225.78, 155.09, 135.51 and 105.62 mm/plant) under different water regime treatments (100, 90, 80, 70, 60 and 50 %) of available moisture holding capacity (AMHC) respectively. Grain yield productions under different treatments were 106.25, 171.25, 127.50, 75, 55 and 40.75 g/plant/pot at 100, 90, 80, 70, 60 and 50 per cent of AMHC respectively. The results showed that water use efficiency (WUE) at different treatments were 0.50, 0.70, 0.56, 0.48, 0.41 and 0.39 g/mm for (100, 90, 80, 70, 60 and 50 %) per cent of AMHC respectively. Therefore, the 90 % of AMHC treatment (T2) is recommended for groundnut irrigation for water saving. The comparison of actual crop coefficient that obtained by water balance technic in experiment and crop coefficient (Kc) values of groundnut for different crop growth stages were selected based on the values suggested by FAO (Allen et al., 1998) are similar in the treatment of 90 % (T2) of the AMHC. Furthermore, the result showed that the treatment of 90 per cent of Available moisture holding capacity (T2) seemed to be better adapted to product a high crop yield with acceptable yield coupling with water use efficiency in this region.

Quantifying riparian total evaporation along the Groot Letaba River: A comparison between infilled and spatially downscaled satellite derived total evaporation estimates

The use of satellite earth observation data for the estimation of evapotranspiration has been well documented and represents a viable approach for the quantification of riparian water use at landscape to regional scales. However, the trade-off between the spatial and temporal resolution associated with imagery can limit the reliability of satellite-based evapotranspiration modelling. This study investigated two approaches to quantify evapotranspiration at a moderate spatial resolution (30 m) on a daily time step, for a perennial river flowing through a semi-arid, savanna landscape. The Surface Energy Balance System (SEBS) Model was used to derive daily evapotranspiration from satellite imagery. The actual crop coefficient (Kcact) and output downscaling with linear regression (ODLR) approaches were then evaluated by comparing their respective estimates against Eddy covariance (ECET) measurements at two locations. Comparisons of ET estimates acquired using the Kcact and ODLR approaches against ECET, yielded RMSE values of; 1.88 and 2.57 mm d−1 and 1.10 and 2.39 mm d−1 (for two replicate transects), respectively. The poor performance of these techniques was largely attributed to the SEBS ET estimates used as inputs to these techniques, as SEBS may overestimate evapotranspiration during conditions of water stress.

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Filed experiment was carried out in land near Ramtha Wastewater Treatment Plant during growing seasons of 2010 and 2011 to determine the effects of using treated wastewater on plant growth, seed yield and yield components of sunflower (Helianthus annuus L.) under trickle irrigation. Randomized complete block design (RCBD) for three irrigation treatments namely; I1= Full irrigation (Actual crop coefficient), I2= 80% of full irrigation and I3= 60% of full irrigation randomized over three blocks. The application efficiency of trickle irrigation system was in the range of 88.2 to 90.8%. The applied irrigation water was 4990, 3992 and 2994 m3 ha-1 in 2010 and 5505, 4404 and 3303 m3 ha-1 in 2011 for I1, I2 and I3 irrigation treatments, respectively. Full irrigation treatment (I1) gave the highest plant height, head diameter, number of seeds plant-1, total weight of seeds plant-1, 1000 seeds weight, and seed and oil yield. Key words: Sunflower production, water shortage, reclaimed wastewater reuse, oilseed crops.

Responses of field evapotranspiration to the changes of cropping pattern and groundwater depth in large irrigation district of Yellow River basin

To solve the problems of decreasing water resources from the Yellow River, the renovation project of water-saving and controlling water distribution was implemented in the Hetao Irrigation District of North China since 1999. The local hydrological cycle is expected to be influenced or changed during the past fifteen years through the project. Jiefangzha Irrigation Region, the second large partition of the Hetao Irrigation District, was selected as the typical area to explore the relationship between agricultural water consumption, water distribution, cropping pattern and changing groundwater level. In this paper, the SEBS (Surface Energy Balance System) model and the ESTARFM (Enhanced Spatial and Temporal Adaptive Reflectance Fusion Model) algorithm were applied to produce daily field-scale evapotranspiration (ET) based on Landsat and MODIS data from 2000 to 2015 at intervals. The results indicate that the cropping pattern had changed greatly, while the water table descended through the years. The total agriculture ET stayed relatively stable, with the average annual consumption of 8.9×108m3. The temporal variation of agriculture ET was not obviously sensitive to the adjustment of cropping pattern. There was no significant difference in April–October ET for different crops, in spite of the clear distinction of ET in each crop-specific growing season. The spatial distribution of agricultural ET did not change in spite of the great adjustment of cropping pattern during fifteen years, which has a close inverse correlation with the groundwater depth. Groundwater depth descended from 1.76m to 2.33m during the operation period of the water-saving project, which might reduce the soil evaporation and have a positive effect on soil salinization effectively. Meanwhile, the net irrigation water use efficiency was improved from 0.59 to 0.66. These effects indicate the positive impact of the implemented water-saving renovation project on water management and environment. However, the actual crop coefficient Kc,a decreased slightly with the gradually increasing reference evapotranspiration, indicating possible drought stress as an effect of the continuing reduction of the availability of net irrigation water and declining groundwater table.

Evaluation of crop coefficients, water productivity, and water balance components for wine grapes irrigated at different deficit levels by a sub-surface drip

Accurate estimation of evapotranspiration (ET) and its partitioning into transpiration and evaporation is fundamental for improving water management practices in water-limited environments and under deficit irrigation conditions. This investigation was conducted to estimate the water balance and ET components of subsurface drip (SDI) irrigated Chardonnay wine grapes for two seasons (2010–2011 and 2011–2012) using a numerical model (HYDRUS-2D). Treatments involved the application of different volumes [51% (I1), 64% (I2), 77% (I3), and 92% (I4) of normal application] of water for irrigation. A modified version of the FAO-56 dual crop coefficient approach was used to generate daily transpiration and evaporation as inputs to the HYDRUS-2D model. The calibrated and validated model produced estimates of actual evapotranspiration (ETCact), actual transpiration (Tpact), and actual evaporation (Esact), and deep percolation under varied irrigation applications. The model-simulated values were then used to estimate actual crop coefficients (Kcact and Kcbact), and water productivity of wine grape under different deficit irrigation conditions.Seasonal ETCact simulated by HYDRUS-2D for different treatments varied between 239 and 382mm. However, seasonal evaporation accounted for 44–59% of seasonal ETCact losses in different treatments. The modelled daily transpiration rate in I4 treatment (Tp4act) varied from 0.11–2.74mm/day. Deep percolation accounted for 35–40% of the total water applied by rainfall and irrigation. The mean value of actual crop coefficient (Kcact) estimated by HYDRUS-2D simulated ETCact over the two seasons was 0.27, which matched with other investigations. Similarly, values of Kcbact for initial, mid and end stages were 0.13, 0.27 and 0.14, respectively. Monthly values of evaporation coefficient (Ke) ranged from 0.1 to 0.32, with a mean value of 0.18. Water productivity with respect to ET losses (WPETC) ranged from 5.9 to 6.2kg/m3 of water use. However, water productivity for transpiration (WPTC) almost doubled as compared to WPETC in all treatments. The impact of deficit irrigation on berry juice composition (Brix, pH and titratable acidity) was lower than the inter-seasonal variability. These results can help develop better irrigation management strategies for SDI irrigated wine grapes under water scarce conditions.

Estimation of Actual Crop Coefficients Using Remotely Sensed Vegetation Indices and Soil Water Balance Modelled Data

A new procedure is proposed for estimating actual basal crop coefficients from vegetation indices (Kcb VI) considering a density coefficient (Kd) and a crop coefficient for bare soil. Kd is computed using the fraction of ground cover by vegetation (fc VI), which is also estimated from vegetation indices derived from remote sensing. A combined approach for estimating actual crop coefficients from vegetation indices (Kc VI) is also proposed by integrating the Kcb VI with the soil evaporation coefficient (Ke) derived from the soil water balance model SIMDualKc. Results for maize, barley and an olive orchard have shown that the approaches for estimating both fc VI and Kcb VI compared well with results obtained using the SIMDualKc model after calibration with ground observation data. For the crops studied, the correlation coefficients relative to comparing the actual Kcb VI and Kc VI with actual Kcb and Kc obtained with SIMDualKc were larger than 0.73 and 0.71, respectively. The corresponding regression coefficients were close to 1.0. The methodology herein presented and discussed allowed for obtaining information for the whole crop season, including periods when vegetation cover is incomplete, as the initial and development stages. Results show that the proposed methods are adequate for supporting irrigation management.

Quantifying evapotranspiration of a rainfed potato crop in South-eastern Canada using eddy covariance techniques

The aim of this study was to quantify the evapotranspiration (ET) of a rainfed potato crop using micrometeorological instrumentation and the eddy covariance techniques (ECV). The ET measurement allowed deriving crop coefficients that vary among the growth season along with indicators that characterize the water use, and it was also used as input to resolve the water balance equation. ET was measured using high-sampling instruments (CSAT3, Campbell SCI Inc.; Li7500, LiCor Inc.), during the growth season of 2007 (20 May–19 September). The cumulative ET was 331.5mm, with a daily maximum of 6.5mm at full coverage; precipitation was 350.6mm which is rather small compared with the historical mean (563.3mm); yield was within the average for this site: 4.02kgm−2; resolving the water balance equation the deep drainage was estimated at 24.7mm. Actual crop coefficients (Kco_act) were determined using the ratio of the actual ET (ETa) and the standardized reference ET (ETo) equation of the American Society of Civil Engineers. Kco_act varied as ETa among the different growing stages, from a mean of 0.63 at vegetative growth to 0.91 at tuber initiation. The productivity of water under rainfall and of water use were respectively 22.1 and 12.1kgm−3.