Crop Coefficient Curves Research Articles

Potential crop evapotranspiration and surface evaporation estimates via a gridded weather forcing dataset

Absent local weather stations, a gridded weather dataset can provide information useful for water management in irrigated areas including potential crop evapotranspiration calculations. In estimating crop irrigation requirements and surface evaporation in Utah, United States of America, methodology and software were developed using the ASCE Standardized Penman-Monteith Reference Evapotranspiration equation with input climate drivers from the North American Land Data Assimilation System (NLDAS) gridded weather forcing dataset and a digital elevation model. A simple procedure was devised to correct bias in NLDAS relative humidity and air temperature data based on comparison to weather data from ground stations. Potential evapotranspiration was calculated for 18 crops (including turfgrass), wetlands (large and narrow), and open water evaporation (deep and shallow) by multiplying crop coefficient curves to reference evapotranspiration with annual curve dates set by summation of Hargreaves evapotranspiration, cumulative growing degree days, or number of days. Net potential evapotranspiration was calculated by subtracting effective precipitation estimates from the Daymet gridded precipitation dataset. Analysis of the results showed that daily estimated potential crop evapotranspiration from the model compared well with estimates from electronic weather stations (1980–2014) and with independently calculated potential crop evapotranspiration in adjacent states. Designed for this study but open sourced for other applications, software entitled GridET encapsulated the GIS-based model that provided data download and management, calculation of reference and potential crop evapotranspiration, and viewing and analysis tools. Flexible features in GridET allows a user to specify grid resolution, evapotranspiration equations, cropping information, and additional datasets with the output being transferable to other GIS software.

Crop Coefficient Curve for Paddy Rice from Residual Energy Balance Calculations

AbstractThe crop coefficient (Kc) values of rice paddy are important for estimating accurate rice crop evapotranspiration (ETc), water transfers planning, efficient irrigation management, and hydrological studies. In this study, ETc was measured and a generalized Kc curve was calculated for paddy rice in the Sacramento Valley, California. Field experiments were conducted in three rice paddy fields during the 2011–2013 growing seasons. Surface renewal analysis, after calibration using eddy covariance method, was applied to obtain sensible heat flux values from high-frequency temperature readings; latent heat flux densities were characterized by the residual of the energy balance method. The results revealed that there is considerable variability in rice water use both spatially and temporally. The average 3-year measured seasonal ETc of the experimental fields ranged from 690 to 762 mm in Butte County and from 681 to 813 mm in the Colusa County. A mean daily seasonal ETc of 5.3 mm d−1 and midseason ETc of...

Estimating water use of mature pecan orchards: A six stage crop growth curve approach

Mature pecans use large quantities of water and therefore the accurate estimation of water use or evapotranspiration (ET) of pecan orchards is critical for judicious irrigation water management and planning. Measuring ET under all possible combinations of climate and management practices is not possible, and as a result, models are used to estimate ET. Empirical modelling approaches are more widely adopted than the more complex mechanistic models, as they are more easily parameterized, but they are not always easily transferred across a wide range of growing conditions, making local evaluation and validation essential. This study evaluated existing crop coefficient models in a mature pecan orchard for three seasons in a semi-arid subtropical climate. Whilst the generic FAO-56 approach, using parameters provided for stone fruit performed reasonably well on a seasonal basis, accurate monthly estimates of ET were not achieved throughout the season. A closer analysis of data from the current study and a previous study in New Mexico, revealed that a six stage crop coefficient curve should be considered for pecans, together with higher mid-season crop coefficient (Kc) values for mature orchards. More accurate estimates of monthly ET for mature pecan orchards were obtained when reference Kc (Kc-ref) values for a well-managed mature pecan orchard in New Mexico were adjusted for local conditions of climate, using a growing degree day—Kc relationship and canopy cover. The adjustment for climate should, however, be used with caution. A comparison between seasons at Cullinan and with New Mexico suggests that whilst thermal time is likely to predict the start of leaf fall, it is unlikely to accurately predict canopy development at the start of the season. As a result it is suggested that in future a crop growth curve based on visual observations of phenological stages is developed.

Evaluation of reference evapotranspiration models and determination of crop coefficient for Momordica charantia and Capsicum annuum

Studies on water balance and irrigation at agricultural areas require accurate values of reference evapotranspiration (ETo). This study was conducted in the agricultural farm in the Modern Agriculture Centre in Kluang, Malaysia, to determine the crop coefficients of bittergourd (Momordica charantia) and chili (Capsicum annuum) by choosing the best ETo model. The experiment was conducted for two different crop cycles between October 2013 and May 2014. An automatic weather station was installed to record weather parameter at 30min interval. Twenty six ETo models which were classified into four different groups were employed. The performance of the models was evaluated using Class A pan evaporation data from Kluang weather station. Eight statistical tests were used to assess and rank the accuracy of these 26 models. The ET values from the best ETo model of each group were then modeled with weather variables using multiple regression technique. Crop coefficient (Kc) curves were developed as the ratio between actual crop evapotranspiration measured by minilysimeters and the ET values of the best model. The temperature based models tend to overestimate observed pan ET values, thus were not recommended at this site. Results of the mass transfer based Penman model show comparatively better ETo estimates among others. The total water requirement for bittergourd for the whole growing period is 153mm while chili recorded 229mm. The Kc values for the bittergourd were 0.58, 0.88 and 0.69 while for chili were 0.58, 0.95 and 0.73 for the initial, mid and end growth stages, respectively. The present results show very similar mid and end season chili Kc values with a study from Ghana while the mid and end season Kc of bittergourd is quite similar with a study in Florida, USA using cucumber. The values obtained can help farmers to determine the water requirement of these vegetable crops so that proper irrigation can be applied according to its growth stage and weather condition.

Development of crop coefficient models of castor and maize crops

Castor and maize are the most commonly cultivated crops in the Rajendranagar region of Andhra Pradesh, India. The study aims to develop a crop coefficient (Kc) models for these crops, using Lysimeter measured daily crop evapotranspiration (ETc) data and daily reference evapotranspiration (ET0) computed using FAO-56 Penman-Monteith (PM) method. Kc values obtained using relationship Kc=ETc/ET0, crop coefficient curves were derived as a function of days after sowing and polynomial model was fitted. The performances of the models were tested using performance indicators. The models performed well for both the crops. These models can, therefore, be used for estimating Kc values of castor and maize crops for any day after sowing in the study region.

Crop water use and stage-specific crop coefficients for irrigated cotton in the mid-south, United States

Regional variations in environmental conditions, cultivars, and management practices necessitate locally derived tools for crop water use estimation and irrigation scheduling. A study was conducted in northeast Louisiana (mid-south US) aimed at estimating daily crop evapotranspiration (ETc) and reference evapotranspiration (ETo) and thus, developing local crop coefficient (Kc) curves for irrigated upland cotton. ETc was determined using paired weighing lysimeters installed near the middle of a 1-ha cotton field and planted with cotton as in the rest of the surrounding field, while ETo was calculated using the Standardized Reference Evapotranspiration Equation (SREE) developed by the American Society of Civil Engineers (ASCE), using estimates of weather variables from a nearby standard reference weather station. Stage-specific Kc values averaged over 2 years were 0.42, 1.25 and 0.70 for initial, midseason, and end season stages of cotton, respectively. The initial-stage Kc value was approximately 26% lower than the Food and Agricultural Organization (FAO)-adjusted initial Kc value. The mid- and end-season Kc values obtained in the study were approximately 6% and 11% greater, respectively, than the FAO-adjusted Kc values for the corresponding stages. The observed differences among the local stage-specific Kc values (especially at initial growth stage of cotton) and the FAO-adjusted initial Kc values could be attributed to regional variations in environmental conditions, cultivars, and management practices. The ETc and Kc values obtained from this study provide research-based information for future studies and the development of Kc-based irrigation tools in this region.

Assessment of a Remote Sensing Energy Balance Methodology (SEBAL) Using Different Interpolation Methods to Determine Evapotranspiration in a Citrus Orchard

A surface energy balance algorithm for land (SEBAL) for estimating evapotranspiration (ET) has been parameterized and tested in a 400-ha drip irrigated citrus orchard. Simultaneously, during three growing seasons, energy fluxes were measured using Eddy Covariance. Instantaneous fluxes obtained with SEBAL using 10 images from Landsat-5 were compared with the measured fluxes. The Perrier function was the best method for properly estimating the roughness momentum length for discontinuous canopies, as in citrus orchards. Crop height was estimated using LIDAR data. In general, SEBAL performed well for net radiation estimation but failed in soil heat flux estimation. Latent heat estimations from the SEBAL model had a relative root mean square error (rRMSE) of 0.06 when compared with measurements obtained by Eddy Covariance. Three procedures were tested for up-scaling the instantaneous ET estimates from SEBAL to daily ET values: 1) assuming the fraction between the actual ET and the reference ET is constant throughout the day; 2) using actual local crop coefficient curves; and 3) using an up-scaling factor where the fraction of hourly ET to daily ET equals the ratio of hourly to daily global solar radiation. This last method gave acceptable results for daily ET estimations $({\bf rRMSE} = {\bf 0.09})$ and for 15-day ET $({\bf rRMSE} = {\bf 0.19})$ , and its main advantage is that no local data are required. It is concluded that the SEBAL methodology can be successfully applied for determining actual ET, even in discontinuous citrus canopies. However, additional parameterizations of momentum roughness length were needed in order to obtain reliable ET determinations.

Estimating Crop Coefficients Using Remote Sensing-Based Vegetation Index

Crop coefficient (Kc)-based estimation of crop evapotranspiration is one of the most commonly used methods for irrigation water management. However, uncertainties of the generalized dual crop coefficient (Kc) method of the Food and Agricultural Organization of the United Nations Irrigation and Drainage Paper No. 56 can contribute to crop evapotranspiration estimates that are substantially different from actual crop evapotranspiration. Similarities between the crop coefficient curve and a satellite-derived vegetation index showed potential for modeling a crop coefficient as a function of the vegetation index. Therefore, the possibility of directly estimating the crop coefficient from satellite reflectance of a crop was investigated. The Kc data used in developing the relationship with NDVI were derived from back-calculations of the FAO-56 dual crop coefficients procedure using field data obtained during 2007 from representative US cropping systems in the High Plains from AmeriFlux sites. A simple linear regression model ( ) is developed to establish a general relationship between a normalized difference vegetation index (NDVI) from a moderate resolution satellite data (MODIS) and the crop coefficient (Kc) calculated from the flux data measured for different crops and cropping practices using AmeriFlux towers. There was a strong linear correlation between the NDVI-estimated Kc and the measured Kc with an r2 of 0.91 and 0.90, while the root-mean-square error (RMSE) for Kc in 2006 and 2007 were 0.16 and 0.19, respectively. The procedure for quantifying crop coefficients from NDVI data presented in this paper should be useful in other regions of the globe to understand regional irrigation water consumption.

Evapotranspiration crop coefficients for mixed riparian plant community and transpiration crop coefficients for Common reed, Cottonwood and Peach-leaf willow in the Platte River Basin, Nebraska-USA

► Evapotranspiration crop coefficients were developed for riparian vegetation . ► Transpiration coefficients were measured for phragmites , willow, cottonwood. ► Vegetation response to flooding caused interannual variability in coefficients. ► Developed coefficients provided robust riparian ET and transpiration estimates. Application of two-step approach of evapotranspiration ( ET ) crop coefficients ( Kc ) to “approximate” a very complex process of actual evapotranspiration ( ETa ) for field crops has been practiced by water management community. However, the use of Kc , and in particular the concept of growing degree days (GDD) to estimate Kc , have not been sufficiently studied for estimation of evaporative losses from riparian vegetation. Our study is one of the first to develop evapotranspiration crop coefficient ( Kc ET ) curves for mixed riparian vegetation and transpiration ( TRP ) crop coefficients ( Kc TRP ) for individual riparian species as a function GDD through extensive field campaigns conducted in 2009 and 2010 in the Platte River Basin in central Nebraska, USA. Kc TRP values for individual riparian vegetation species [Common reed (Phragmites australis), Cottonwood (Populus deltoids) and Peach-leaf willow (Salix amygdaloides)] were quantified from the TRP rates obtained using scaled-up canopy resistance from measured leaf-level stomatal resistance and reference evapotranspiration. The Kc ET and Kc TRP curves were developed for alfalfa-reference ( Kcr ET and Kcr TRP ) surface. The seasonal average mixed riparian plant community Kcr ET was 0.89 in 2009 and 1.27 in 2010. In 2009, the seasonal average Kcr TRP values for Common reed, Cottonwood and Peach-leaf willow were 0.57, 0.51 and 0.62, respectively. In 2010, the seasonal average Kcr TRP were 0.69, 0.62 and 0.83 for the same species, respectively. In general, TRP crop coefficients had less interannual variability than the Kcr ET . Response of the vegetation to flooding in 2010 played an important role on the interannual variability of Kcr ET values. We demonstrated good performance and reliability of developed GDD-based Kcr TRP curves by using the curves developed for 2009 to predict TRP rates of individual species in 2010. Using the Kcr TRP curves developed during the 2009 season, we were able to predict the TRP rates for Common reed, Cottonwood and Peach-leaf willow in 2010 within 7%, 8% and 13% accuracy, indicating a good performance of the two-step approach proposed in this study for estimating TRP for riparian vegetation. The surface conditions of the riparian ecosystem need to be considered when using the two-step approach to estimate ETa or TRP rates of riparian plant communities. The results of this study provide important water use information and data for riparian vegetation that can be used for more robust hydrologic/water balance analyses.

Comparison of Reference Evapotranspiration Calculations for Southeastern North Dakota

Potential water consumption for irrigation scheduling in North Dakota was typically calculated from a reference Evapotranspiration (ETref) using the Jensen-Haise method and its associated crop coefficient (Kc) curves developed in the 1970’s and 1980’s. The ETref method proposed by the American Society of Civil Engineers, Environmental and Water Research Institute (ASCE-EWRI) reference evapotranspiration task force has shown to be more accurate and therefore more widely used than any other methods. However, to apply the ASCE-EWRI method for irrigation scheduling requires a corresponding change of the Kc curves associated with the Jensen-Haise method. In this paper, a comparison of ETref estimates for 11 methods, including the ASCE-EWRI and the Jensen-Haise methods, was conducted using 18 years of data collected in southeastern North Dakota. The results show that the annual ETref by the Jensen-Haise method was nearly the same as the ASCE-EWRI grass ETref, but with a higher Root Mean Square Deviation (RMSD), 0.903 mm d-1, and a lower coefficient of determination (R2) 0.8659. The ETref comparison for the growing season only shows an RMSD of 1.007 mm d-1, R2 of 0.7996 and 8.13% overestimation. The ETref by the Jensen-Haisemethod has a higher monthly ETref than the ASCE-EWRI in June, July, and August, and a lower monthly ETref for all other months in an 18 year period. The ETref comparisons also show that the modified Penman method used by the High Plains Regional Climate Center (HPRCC Penman) has the best accuracy and correlation with the ASCE-EWRI ETref method. Indeed, all alfalfa based ETref methods, including Kimberly Penman and HPRCC Penman, show better performance than the grass based ETref methods, including FAO24 Penman, FAO24 Radiation, FAO24 Blaney-Criddle, Priestley-Taylor, Hargreaves, and the Jensen-Haise methods.

Combining the Crop Coefficient of Winter Wheat and Summer Maize with a Remotely Sensed Vegetation Index for Estimating Evapotranspiration in the North China Plain

Estimates of actual evapotranspiration (ETc) in the wheat and maize fields are essential in effective planning of irrigation water use in the North China Plain. A widely used method for ETc estimation in agriculture is crucially dependent on the determination of crop coefficient curves. Estimating the coefficient coefficients from vegetation index (VI) is useful for regional ETc simulation because the VI can represent the actual crop conditions and capture the spatial variability. In this study, the basal crop coefficient and soil evaporation coefficient were combined with the commonly used VI obtained from satellite sensor based on the observed data from a flux tower. The basal crop coefficient had a fairly good linear relationship with the VI, and the soil evaporation coefficient was well related to the vegetation fraction, which was calculated from the VI. Using the VI-derived crop coefficient curves, ETc can be well simulated by a widely used ETc estimation method. Moreover, simulation of ETc was improved by the VI-derived basal crop coefficient curves. The new relationships between the crop coefficients and VI employed in the dual crop coefficient approach have great potential in the estimation of regional ETc in the region.

Improving evapotranspiration simulations in the CERES-Maize model under limited irrigation

Limitations on water resources for agriculture in places such as Colorado, USA, have caused farmers to consider limited irrigation as an alternative to full irrigation practices, where the crop is intentionally stressed during specific growth stages in an effort to maximize yield per unit water consumed, or evapotranspiration (ET). While crop growth models such as CERES-Maize provide the ability to evaluate numerous management scenarios without the costs associated with multiyear field experiments, recent studies have shown that CERES-Maize performs well under full irrigation but overestimates ET of corn under limited irrigation management. The primary objective of this study was to improve CERES-Maize ET simulation under limited irrigation management while maintaining accuracy of other important model output responses. Field experiments with corn were performed in northern Colorado, USA from 2006 to 2010, where four replicates each of full (ET requirement supplied by irrigation throughout the season) and limited (no irrigation before the V12 growth stage unless necessary for emergence, then full irrigation afterwards) irrigation treatments were analyzed. The local sensitivity of model input parameters affecting ET was evaluated, prompting changes to the model code with a new dynamic crop coefficient (KCD) as a function of the crop leaf area index. The modified CERES-Maize model more accurately represented ET under full and limited irrigation, for example reducing late-season ET potential from a plant with reduced canopy and more closely matched FAO-56 crop coefficient curves under full irrigation. Using the limited irrigation data for evaluation, the modified model showed significant decreases in model error for seasonal cumulative ET (root mean square deviation RMSD from 80.9mm to 49.9mm) and water productivity (RMSD from 5.97kgha−1mm−1 to 2.86kgha−1mm−1) as compared to the original model. The modified model was subsequently applied to several hypothetical irrigation management strategies, indicating that reducing weekly vegetative stage water applications from 20mm to 2.5mm can increase simulated water productivity by over 15%. While these synthetic water production functions may not be feasible in a production field with natural climate variability, the modified ET model indicates promise for limited irrigation management increasing water productivity.

Comparison of irrigation scheduling strategies for achieving water use efficiency in highbush blueberry

A glasshouse experiment was carried out to assess the feasibility of applying partial rootzone drying (PRD) to highbush blueberries (Vaccinium corymbosum). A subsequent field experiment was established to assess four irrigation strategies with the aim of improving water use efficiency in blueberry production. Applying PRD to plants during a glasshouse experiment reduced stomatal conductance without reducing plant water potential. Hindered by high rainfall, a physiological response to PRD was not repeated in field grown plants. However, irrigation scheduled using a Kc (crop coefficient) curve constructed from Food and Agriculture Organization (FAO) 56 guidelines and post-harvest regulated deficit irrigation (RDI) delivered annual water savings of 0.8 ML ha−1 and 1.3 ML ha−1, respectively, compared with a total 3.6 ML ha−1 applied using a ‘rule-of-thumb’ approach commonly adopted by Australian blueberry growers. These savings were achieved without reducing berry yield or quality. This study is the first to report on the feasibility of applying FAO 56 guidelines, RDI and PRD as strategies to maximize water use efficiency in highbush blueberry production.

Satellite‐based ET estimation in agriculture using SEBAL and METRIC

AbstractSurface Energy Balance Algorithms for Land (SEBAL) and Mapping EvapoTranspiration at high Resolution with Internalized Calibration (METRIC) are satellite‐based image‐processing models that calculate evapotranspiration (ET) as a residual of a surface energy balance. Both models are calibrated using inverse modelling at extreme conditions approach to develop image‐specific estimations of the sensible heat flux (H) component of the surface energy balance and to effectively remove systematic biases in net radiation, soil heat flux, radiometric temperature and aerodynamic estimates. SEBAL and METRIC express the near‐surface temperature gradient as an indexed function of radiometric surface temperature, eliminating the need for absolutely accurate surface temperature and the need for air temperature measurements. Slope and aspect functions and temperature lapsing are used in METRIC applications in mountainous terrains. SEBAL and METRIC algorithms are designed for relatively routine application by trained professionals familiar with energy balance, aerodynamics and basic radiation physics. The primary inputs for the models are short‐wave and long‐wave (thermal) images from satellite (e.g. Landsat and MODIS), a digital elevation model and ground‐based weather data measured within or near the area of interest. ET ‘maps’ (i.e. images) developed using Landsat images provide means to quantify ET on a field basis in terms of both rate and spatial distribution. METRIC takes advantage of calibration using weather‐based reference ET so that both calibration and extrapolation of instantaneous ET to 24‐h and longer periods compensate for regional advection effects where ET can exceed daily net radiation. SEBAL and METRIC have advantages over conventional methods of estimating ET using crop coefficient curves or vegetation indices in that specific crop or vegetation type does not need to be known and the energy balance can detect reduced ET caused by water shortage, salinity or frost as well as evaporation from bare soil. Copyright © 2011 John Wiley & Sons, Ltd.

Developement of crop coefficient curves for different growth periods of kharif groundnut

Developement of crop coefficient curves for different growth periods of kharif groundnut

Water use, crop coefficients, and irrigation management criteria for camelina production in arid regions

Camelina sativa (L.) Crantz is an oilseed crop touted as being suitable for production in the arid southwestern USA. However, because any significant development of the crop has been limited to cooler, rain-fed climate-areas, information and guidance for managing irrigated-camelina are lacking. This study measured the crop water use of a November-through-April camelina crop in Arizona using frequent measurements of soil water contents. The crop was grown under surface irrigation using five treatment levels of soil water depletion. The seed yields of treatments averaged 1,142 kg ha−1 (8.0% seed moisture) and were generally comparable with camelina yields reported in other parts of the USA. Varying total irrigation water amounts to treatments (295–330 mm) did not significantly affect yield, whereas total crop evapotranspiration (ETc) was increased for the most frequently irrigated treatment. However, total ETc for the camelina treatments (332–371 mm) was markedly less than that typically needed by grain and vegetable crops (600–655 mm), which are commonly grown during the same timeframe in Arizona. The camelina water-use data were used to develop crop coefficients based on days past planting, growing degree days, and canopy spectral reflectance. The crop coefficient curves, along with information presented on camelina soil water depletion and root zone water extraction characteristics will provide camelina growers in arid regions with practical tools for managing irrigations.

Irrigation Planning in Command Areas Using Crop Coefficient Model

In the Lower Bhavani Project command area, Tamil Nadu an investigation was carried out to develop crop coefficient model for groundnut. With the obtained crop coefficient values, crop coefficient curve was derived as a function of days after sowing (DAS) and polynomial model was fitted. Using the derived polynomial equation, crop coefficient values of this crop for any day after sowing can be estimated for LBP command. The equation of the regression model of crop coefficient can therefore, be used for estimation of water requirement of this crop grown in LBP command area. It could also be valid for other areas having similar climatic conditions where such data are either not generated experimentally or available at all.

Single and dual crop coefficients and water requirements for onion ( Allium cepa L.) under semiarid conditions

The objectives of this study were to determine onion water requirements with a sprinkler irrigation system, the most usual irrigation method in Spain. A weighing lysimeter was used to measure single (Kc) and dual (Kcb + Ke) crop coefficient curves and obtain the relationship between Kc-ground cover (GC) and Kcb-GC. Experimental work was carried out in 2005 at “Las Tiesas” farm, located in Albacete (Central Spain). To determine actual onion evapotranspiration (ETc), we used a weighing lysimeter with continuous electronic data recording. Daily measured ETc values obtained by the lysimeter were compared to calculated ETc values obtained through the standard FAO methodology [Allen, R.G., Pereira, L.S., Raes, D., Smith, M., 1998. Crop evapotranspiration. Guidelines for computing crop water requirements. FAO Irrig. and Drain. Paper 56. Rome, Italy]. Seasonal evapotranspiration measured in the lysimeter (893.34 mm) was higher than the seasonal ETc calculated by FAO-56 method (832.90 mm). The percentage of GC was found through the supervised classification technique of digital photographic images with the maximum probability algorithm [Calera, A., Martínez, C., Melia, J., 2001. A procedure for obtaining green plant cover: relation to NDVI in a case study for barley. Int. J. Remote Sensing, 22, 3357–3362]. The values derived from lysimetric measurements are Kc ini: 0.65, Kc mid: 1.20 and Kc end: 0.75, similar to values given in FAO-56. Lysimetric measurements showed that the evaporative component was high during the growing season, due to the high frequency of irrigation and the fact that the onion crop does not completely cover the ground; maximum GC was 72%. Therefore, the dual crop coefficient was calculated, which allowed differentiation between crop transpiration (basal crop coefficient, Kcb) and evaporation from the soil (evaporation coefficient, Ke). With the aim of facilitating extrapolation of the results to other areas, Kc and Kcb were linearly correlated to fractional GC.

WATER REQUIREMENTS FOR IRRIGATED SUGARCANE UNDER TRICKLE IRRIGATION

Effect of irrigation water requirements and row spacing of surface and subsurface trickle irrigated sugarcane on soil moisture distribution, sugarcane yield, sugar percentage and water use efficiency were studied. There are three different lateral distance between plants (L) used in the experiment; 0.75 m, 1.00 m and 1.25 m under four irrigation treatments; 70%, 85%, 100% and 115% from water requirements of sugarcane. Soil moisture content was affected by different water requirements and row spacing. While the average soil moisture content in the upper layer (0 – 20cm) under subsurface trickle irrigation was less than under surface trickle irrigation, it was in subsurface trickle irrigation more than in surface trickle irrigation in lower layer (30 – 50cm). The results of this work indicated that the maximum yield production is 70 ton/fed under surface trickle irrigation system, 1.25 m distance between plants and at 85% of water requirements of sugarcane. Also the results indicated that the maximum yield production is 70 ton/fed under sub-surface trickle irrigation system, 1.00 m and 1.25 m distance between plants and at 100% and 85% of water requirements of sugarcane respectively. A crop coefficient curve for sugarcane was plotted for measuring crop evapotranspiration.

Water Requirement of Irrigated Garlic

A replicated field trial was conducted on the west side of the San Joaquin Valley to determine the crop coefficient and water requirements of irrigated garlic. Irrigation systems used included simulated furrow irrigation, subsurface drip irrigation, and surface drip irrigation. Irrigation levels were set at 50%, 75%, 100%, and 125% of crop evapotranspiration (ETc) measured with a weighing lysimeter. Field plots consisted of four beds 80 m long and a 1 m wide, with the two inside beds used for experimental purposes and the outside beds as buffers. Irrigation scheduling was controlled by the crop lysimeter using ETc threshold values: 1 mm for the subsurface drip irrigation, 2 mm for the surface drip irrigation, and a weekly irrigation equal to the accumulated ETc for the simulated furrow irrigation treatment. The crop water use at 100% ETc for the interval 1 March to 21 May 2006 was 426 mm, including 108 mm of rainfall. The irrigation schedule was modified to reflect the rainfall contribution during the experimental period. An asymptote was used to relate yield to the applied water and the total water use. Maximum yield occurred at 100% ETc, and irrigation in excess of 100% ETc did not provide any additional yield. Statistically, there was very little difference in the yield parameters and quality parameters when compared across irrigation system types. Statistical differences occurred between the irrigation levels. Peak crop coefficient values were estimated in the range of 1.3 to 1.4. The Kc was linearly related to the day of the year. This represents the development segment of the crop coefficient curve as described in FAO Irrigation and Drainage Paper 56.