Local Crop Coefficients Research Articles

Productivity of olive oil (Coratina variety) in response to irrigation treatments in sandy soil

AbstractA 2‐year field experiment was conducted on drip‐irrigated olive oil orchards (Coratina var.) on a private farm in the newly reclaimed sandy soil of the West Nile Delta region, Egypt, during the 2020 and 2021 seasons to evaluate the effect of five irrigation treatments (120%, 100%, 80% and 60% reference crop evapotranspiration [ETo] and farmer practice) on applied irrigation water (AIW), water consumptive use, olive fruit and oil yields and some fruit quality parameters, water use efficiency, water productivity, electric energy consumed, farm income and benefit–cost ratio and to develop local crop coefficients (Kc) and yield response factors (Ky). The results indicated that the 2‐year average AIW values were 9953 (17.9 m3/tree/year), 8484 (15.3 m3/tree/year), 6971 (12.5 m3/tree/year), 5480 (9.9 m3/tree/year) and 17,488 m3/ha (31.5 m3/tree/year) for the tested irrigation treatments. Olive fruit and oil yields and quality parameters were significantly affected by the tested treatments. The highest fruit and oil yields were recorded for the 120% ETo treatment. A seasonal Kc of 0.75 and a seasonal Ky of 0.83 were obtained. It can be concluded that producing oil from olive trees (Coratina var.) in sandy soils can be achieved by applying amounts of water equal to 80% or 60% ETo.

Irrigation Water and Nitrogen Fertilizer Management in Potato (Solanum tuberosum L.): A Review

Intensive irrigation and nutrient management practices in agriculture have given rise to serious issues in aquifer water depletion and groundwater quality. This review discusses the effects of irrigation and nitrogen management practices on potato growth, yield, and quality, and their impacts on water and nitrogen use efficiencies. This review also highlights the economics and consequences of applying deficit irrigation strategies in potato production. Many researchers have demonstrated that excessive irrigation and nitrogen application rates negatively impact potato tuber yield and quality while also increasing nitrate leaching, energy consumption, and the overall costs of production. An application of light-to-moderate deficit irrigation (10–30% of full irrigation) together with reduced nitrogen rates (60–170 kg/ha) has a great potential to improve water and nitrogen use efficiencies while obtaining optimum yield and quality in potato production, depending on the climate, variety, soil type, and water availability. There is an opportunity to reduce N application rates in potato production through deficit irrigation practices by minimizing nitrate leaching beyond the crop root zone. The best irrigation and nitrogen management techniques for potato production, as discussed in this review, include using sprinkle and drip irrigation techniques, irrigation scheduling based on local crop coefficients, soil moisture content, and crop modeling techniques, applying slow-release nitrogenous fertilizers, split nitrogen application, and applying water and nitrogenous fertilizers in accordance with crop growth stage requirements.

Accuracy of Estimated Crop Evapotranspiration Using Locally Developed Crop Coefficients against Satellite-Derived Crop Evapotranspiration in a Semiarid Climate

Actual crop evapotranspiration (ETa) is measured or estimated using different methods, and its accuracy is critical for water management under precision agriculture. The objective of this study was to compare maize ETa estimated by the two-step approach using a locally developed crop coefficient curve with satellite-retrieved evapotranspiration by six models incorporated in the OpenET to identify the best evapotranspiration estimation alternatives to the two-step approach for water management in northern New Mexico. Maize (Zea mays L.) was planted at the NMSU Agricultural Science Center at Farmington from 2017 to 2022 and uniformly managed across years. Water management in plants was based on maize’s actual evapotranspiration estimated as the product of the reference evapotranspiration and the local crop coefficient, which is described as a third-order polynomial function of the accumulated heat units by maize plants. For the same growing seasons, maize ETa was retrieved from satellite, and was estimated by six models listed within the OpenET from 2017 to 2022. The results show that maize daily ETa was consistently smaller when measured by SIMS and PT-JPL during maize initial and actively growing stages, while ETc(kc), SIMS and eeMETRIC showed similar maize daily ETa during maize full canopy development and mid-season, and which overcome the evapotranspiration estimated by DisALEXI, PT-JPL, geeSEBAL, and SSBop. ETc(kc) drastically dropped and became the lowest value among all ETa estimation models after the first fall snow or the first killing frost. Regarding the seasonal average, all six models included in OpenET showed smaller maize evapotranspiration. Maize seasonal evapotranspiration varied from 589.7 to 683.2 mm. eeMETRIC compares most similarly to the ETc(kc) model, followed by SIMS, with percent errors of 2.58 and 7.74% on a daily basis and 2.43 and 7.88% on a seasonal basis, with the lowest MBE and RMSE values, respectively, and could be used as an alternative for maize actual daily evapotranspiration for water management in northern New Mexico. The results of this study could be used by water managers and crop growers to improve water management in the Four Corners region, using eeMETRIC for crop water use to improve water management and conservation under sustainable agriculture.

The Agricultural Water Footprint of Al-Qadisiyah Governorate, Southern Iraq

Rapid urbanization, pollution, and increasing water consumption together with climate change necessitated to process of more effective measurement, management, and decision mechanisms on regional water resources. The concept of water footprint (WF) is a parameter that has been introduced to the scientific literature in recent years similar to the ecological and carbon footprints. The WF of any field or product refers to the total volume of water resources that are processed or contaminated directly or indirectly during the production process. The current work is the first study assessing and discussing the agricultural water footprint of an Iraqi governorate by analyzing blue and green WFs of agricultural production in Qadisiyah governorate, southern Iraq for 2010-2020. Recently developed WF methodology has been used. The blue and green evapotranspiration amounts were estimated by the crop water requirement (CWR) option in CROPWAT 8.0 software. The statistical data including meteorological data, rainfall statistics, local crop coefficients, cultivation area, crop production amounts and animal statistics data have been utilized. The average annual agricultural WF of Qadisiyah governorate for the 10 years between 2010-2020 was determined to be 1,315,201,621 Mm3/yr. The largest water-consuming sector is crop production (54%). Cereal and feed crops are the main component of water consumption. The rice crop followed by wheat is the primary crop production comprising about 44% of the total WF and require water supplied from rivers. Vegetable production has only 14% of the crops WF. The green WF was only 15% of the crop production WF. The largest share of water used for animal production is related to broiler chickens (44%) and 37% for dairy cattle. The study area is fertile land for crop production. However, limited water resources and scarcity of the region restrict the agricultural activities. The sustainability of freshwater resources of the governorate could be provided by reducing the WF and blue water contents. This study is expected to contribute to the national authorities to develop more accurate irrigation water management policies.

Evapotranspiration estimation using a modified crop coefficient model in a rotated rice-winter wheat system

Understanding the process of crop evapotranspiration (ETc) and developing models for estimating ETc are crucial to efficiently schedule irrigation and enhance efficient water use. Here, we investigated variations of ETc and local crop coefficient (Kc = ETc / ETo, where ETo is the reference evapotranspiration) in a rotated flooded rice-winter wheat system using ETc data based on the Bowen-ratio energy balance method from 2016 to 2020. We propose a modified Kc model for estimating daily ETc, which includes a density coefficient (a function of fraction of canopy cover) and incorporates the effect of plant temperature constraint, leaf senescence, and water stress on ETc. Results indicated that the total ETc over whole growth stage for flooded rice and winter wheat field was 500.2 ± 62.5 and 298.6 ± 28.3 mm (means ± standard deviation), respectively. The values of local Kc at the initial, middle, and late stages were 0.83 ± 0.14, 1.11 ± 0.06, and 0.99 ± 0.15, respectively, for flooded rice and 0.71 ± 0.08, 0.86 ± 0.06, and 0.76 ± 0.08, respectively, for winter wheat. There was no water stress over the entire season of the flooded rice-winter wheat rotation system except for some days with water draining in paddy rice field. Heat stress in summer adversely affected the ETc of rice. The modified Kc model can well reproduce the values of daily ETc for both flooded rice and winter wheat, and improved the accuracy by 6~9% compared to the FAO 56 Kc model using tabulated values after adjustment. The regression coefficient, coefficient of determination, root mean squared error and modeling efficiency between measured ETc and estimated by the modified Kc model were 0.99, 0.89, 0.55 mm d−1 and 0.89, respectively, for flooded rice, and 1.03, 0.85, 0.55 mm d−1 and 0.82, respectively, for winter wheat. Therefore, the modified Kc model could reasonably predict ETc for flooded rice and winter wheat and can serve as a useful tool to improve water use.

Comparative Evaluation of Simplified Surface Energy Balance Index-Based Actual ET against Lysimeter Data in a Tropical River Basin

In the past decades, multispectral and multitemporal remote sensing has been popularly used for estimating actual evapotranspiration (ETc) across the globe. It has been proven to be a cost-effective tool for understanding agricultural practices in a region. Today, because of the availability of different onboard sensors on an increasing number of different satellites, land surface activity can be captured at fine spatial and time scales. In the present study, three multi-date satellite imageries were used for the evaluation of remote sensing-based estimation of actual evapotranspiration in paddy in the command area of the tropical Kangsabati river basin. A surface energy balance model, the Simplified-Surface Energy Balance Index (S-SEBI), was applied for all three dates of the Rabi season (2014–2015) for the estimation of actual evapotranspiration. The crop coefficient was calculated using the exhaustive survey data collected from the command area and adjusted to local conditions. The ETc estimated using the S-SEBI-based model was compared with the Food and Agriculture Organization Penman–Monteith (FAO-56 PM) method multiplied by the adjusted local crop coefficient and lysimeter data in the command area. The coefficient of determination (r2) was applied to examine the accuracy of the S-SEBI model with respect to lysimeter data and the FAO-56 PM-based ETc. The results showed that the S-SEBI model performed well with the lysimeter (r2 = 0.90) in comparison with FAO-56 PM, with an r2 of 0.65. In addition to this, the S-SEBI-based ET estimates correlated well with the FAO-56 PM, with r and RMSE values of 0.06 and 1.13 mm/day (initial stage), 0.85 and 0.48 mm/day (development stage), and 0.77 and 0.52 (maturity stage) for paddy, respectively. The S-SEBI-based ETc estimate varied with different stages of crop growth and successfully captured the spatial heterogeneity within the command area. In general, this study showed that the S-SEBI method has the potential to calculate spatial evapotranspiration and provide useful information for efficient water management. The results revealed the applicability and accuracy of remote sensing-based ET for managing water resources in a command area with scarce data.

Irrigation-Advisor—A Decision Support System for Irrigation of Vegetable Crops

Climate change will intensify water scarcity, and therefore irrigation must be adapted to save water. Operational tools that provide watering recommendations to end-users are needed. This work presents a new tool, Irrigation-Advisor (IA), which is based on weather forecasts and is able to separately determine soil evaporation and crop transpiration, and thus is adaptable to a broad range of agricultural situations. By calculating several statistical indicators, IA was tested against the FAO-56 crop evapotranspiration (ETcFAO) methodology using local crop coefficients. Additionally, IA recommendations were compared with current standard practices by experienced farmers (F). Six field experiments with four widely cultivated species (endive, lettuce, muskmelon and potato) were performed in Southeast Spain. Irrigation water applied, crop yield, aboveground biomass and water productivity were determined. Crop water needs underestimations (5%–20%) were detected when comparing IA against ETcFAO, although the index of agreement proved reasonable adjustments. The IA recommendations led to water savings up to 13% when compared to F, except for lettuce, with a 31% surplus in irrigation when using IA. Crop yield was not compromised and water productivity was increased by IA. Therefore, IA mimicked the farmers′ irrigation strategies fairly well without deploying sensors on-site. Nevertheless, improvements are needed for increasing the accuracy of IA estimations.

A hybrid approach combining the FAO-56 method and the complementary principle for predicting daily evapotranspiration on a rainfed crop field

In this study, we proposed a hybrid approach combining the standard FAO-56 method with the complementary principle of evapotranspiration (ET) to predict actual ET (ETa) on a rainfed crop field. A generalized complementary relationship (GCR) was employed to quantify the water stress coefficient (Ks) for the FAO-56 method with no use of soil moisture data. Then, the Ks values were multiplied to the crop ET (ETc) estimated with the corrected air temperatures for the assumption of adequate land-surface moisture. The proposed hybrid method applied to a rotational maize-soybean field where an eddy-covariance flux tower was installed. Results showed that the reference ET (ETo) estimated by the corrected temperatures was within a range of 89–95% of that from non-corrected ones, implying that ETo could be inflated when using the mean air temperatures measured under sub-humid conditions. The Ks values estimated by GCR showed consistent patterns with temporal rainfall variation on the field. The multiplication of the Ks from GCR and ETc showed higher performance in ETa prediction than when the GCR was solely applied. By inverting the hybrid approach, a local crop coefficient curve for the rainfed maize field was developed, and led to further improvement in ETa prediction. This study suggests that combination of the complementary principle and the FAO-standard method, which are seemingly in separate paradigms, may improve ETa prediction on crop fields.

Water use efficiency of corn among the irrigation districts across the Duero river basin (Spain): Estimation of local crop coefficients by satellite images

Irrigation in the Duero river basin accounts for 75% of total water resources. Nevertheless, irrigation in this area is paramount to maintain agricultural production. Within this context, this paper is aimed at assessing the water use efficiency (WUE), for the major crop (corn), among four irrigation districts (IDs) from 2014 to 2017. Since the WUE indicators base upon crop water requirements, these were calculated by estimating the reference evapotranspiration and the local crop coefficients Kc. First, they were estimated by satellite images and then, compared with the recommendation from the Regional Irrigation Advisory Service. Finally, the gross irrigation requirements were compared with the irrigation supply.WUE indicators varied among IDs depending upon the hydrologic year, the water available for irrigation (superficial and subsurface water), and the corn sowing date. Usually, the IDs performed deficit irrigation in the dry years, and either full irrigation or over irrigation in the wet years. The rainfall only fulfilled less than 10% of corn requirements. Small differences in Kc were observed within municipalities (in each ID) and/or among IDs. The pattern of the Kc fitted curves varied among IDs and was affected by sowing dates.Although, the local Kc values were close to the general coefficients recommended by the Irrigation Advisory Service, they affected the determination of gross irrigation requirements which were significant different among IDs. Moreover, it was observed that the FAO recommendation for the duration of the corn growth stages fitted better the estimated Kc than the one from the Advisory Center.The gross irrigation requirements were similar among IDs and years, varying between 6476 and 7646 m3/ha. The local Kc estimation could help irrigation managers to adapt the irrigation supply to the actual corn needs.

Estimating strawberry crop coefficients under plastic tunnels in Southern Spain by using drainage lysimeters

Abstract Water is the major limiting factor in the irrigated agriculture of Southern Spain. This fact is even more determining for strawberries cultivated in the vicinity of environmentally sensitive areas such as the Donana National Park; the major protected wetland of Europe. In the last few years, there is a growing interest on maximizing the efficient use of irrigation water in this area, aiming to achieve the equilibrium between agricultural practices and environmental protection. This work shows the local crop coefficients (Kc) for strawberries (Fragaria x ananassa cv. Sabrina) grown under plastic tunnels in the coast of Huelva (Spain). Crop coefficients were estimated in situ during the 2014/15 and 2015/16 seasons by using three drainage lysimeters installed along the raised beds where plants were grown, and filled with the same soil (sandy soil). Estimated Kc values were defined on the basis of the agro-climatic information provided by two weather stations located inside and outside of the tunnels (macro-tunnels). Values ranged between 0.3 and 0.8, when outside data were used, and between 0.4 and 1.4, when using the climatic data provided by the weather station inside the macro-tunnel. However, discrepancies in estimations of Kc inside were observed depending on the methodology used to determine the reference evapotranspiration (ET0) under the plastic tunnel. Polygonal and polynomial models were fitted to Kc data versus the days after planting (DAP) and the growing degree days (GDD) in order to provide a useful tool for growers to be able to estimate crop water needs. These results represent an important contribution for the improvement of irrigation water use in strawberry cultivation in the Southern Spain.

Virtual water flows and water-footprint of agricultural crop production, import and export: A case study for Israel.

Agriculture is the largest global consumer of freshwater. As the volume of international trade continues to rise, so does the understanding that trade of water-intensive crops from areas with high precipitation, to arid regions can help mitigate water scarcity, highlighting the importance of crop water accounting. Virtual-Water, or Water-Footprint [WF] of agricultural crops, is a powerful indicator for assessing the extent of water use by plants, contamination of water bodies by agricultural practices and trade between countries, which underlies any international trade of crops. Most available studies of virtual-water flows by import/export of agricultural commodities were based on global databases, which are considered to be of limited accuracy. The present study analyzes the WF of crop production, import, and export on a country level, using Israel as a case study, comparing data from two high-resolution local databases and two global datasets. Results for local datasets demonstrate a WF of ~1200Million Cubic Meters [MCM]/year) for total crop production, ~1000MCM/year for import and ~250MCM/year for export. Fruits and vegetables comprise ~80% of Export WF (~200MCM/year), ~50% of crop production and only ~20% of the imports. Economic Water Productivity [EWP] ($/m3) for fruits and vegetables is 1.5 higher compared to other crops. Moreover, the results based on local and global datasets varied significantly, demonstrating the importance of developing high-resolution local datasets based on local crop coefficients. Performing high resolution WF analysis can help in developing agricultural policies that include support for low WF/high EWP and limit high WF/low EWP crop export, where water availability is limited.

CROP COEFFICIENT REGIONALIZATION FOR IRRIGATED AGRICULTURE PLANNING IN MARANHÃO STATE -BRAZIL

ABSTRACT: Irrigated agriculture has emerged as a necessary technology to achieve greater productivity, mainly by supplying the water requirements of agricultural crops in critical periods, especially for those regions where natural rainfall is insufficient to meet these requirements. The daily water consumption of crops is strongly influenced by local weather conditions, which justifies the need for regionalized studies of the parameters influencing the water depth to be applied. The crop coefficient (Kc) is perhaps the most important parameter because it interferes directly with the crop water requirements. This index must be determined for each region, thus avoiding the use of reference values meant for other climatic conditions, causing loss of productivity The present study aimed to estimate the local crop coefficients for corn (Zea mays L.) for the climatic conditions of the State of Maranhao, aiming at the rational use of water in agriculture. The method, which allowed obtaining the local values of Kc for different phases of the crop cycle, used climatic data from 12 weather stations (INMET) and mathematical equations proposed by Albuquerque et al. (2001). It estimated the mean and final Kc values. The local values of Kc obtained for corn ranged from 0.73 to 0.77, 1.00 to 1.31, and 0.24 to 0.45 for initial, intermediate, and final phases, respectively.

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.

Determination of an efficient irrigation schedule for the cultivation of rose cv. Freedom under greenhouse conditions in Colombia

An experiment on rose (Rosa sp.) cv. Freedom was performed in a greenhouse on the Bogota Plateau, Colombia, to identify an efficient irrigation regime for this crop. The tested treatments were based on three irrigation doses, applying different fractions of the estimated crop evapotranspiration (ETc), calculated using a class A evaporation tank: i) 100% ETc (ETc100), ii) 80% ETc (ETc80) and iii) 70% ETc (ETc70). During the entire experimental period, from mid-May to early September, the crop had a constant production of floral stems. In all of the irrigation treatments, the soil and plant water status were monitored using tensiometers and the midday stem water potential, respectively (ystem). In the fully irrigated roses, the actual water use was determined using a drainage lysimeter in order to obtain the local crop coefficients (Kc) by means of a water balance. From June to August, the obtained monthly Kc values varied between 1.10 and 1.26. Compared to the ETc100 treatment, 14.5 and 21.8% less water was applied in treatments ETc80 and ETc70, respectively. Despite this fact, no statistically significant differences were found among the treatments for rose production or quality. Finally, in the more irrigated roses, tight relationships between the stem water potential and vapor pressure deficit were obtained. The reported base-line equations can be used for predicting the optimum rose plant water status, depending on the environmental conditions. Overall, the reported results can be used for an efficient irritation schedule for rose crops under greenhouse conditions, using the local Kc and direct determinations of plant water status corrected for the evaporative demand.

Using the dual approach of FAO-56 for partitioning ET into soil and plant components for olive orchards in a semi-arid region

The main goal of this research was to evaluate the potential of the dual approach of FAO-56 for estimating actual crop evapotranspiration (AET) and its components (crop transpiration and soil evaporation) of an olive (Olea europaea L) orchard in the semi-arid region of Tensift-basin (central of Morocco). Two years (2003 and 2004) of continuous measurements of AET with the eddy-covariance technique were used to test the performance of the model. The results showed that, by using the local values of basal crop coefficients, the approach simulates reasonably well AET over two growing seasons. The Root Mean Square Error (RMSE) between measured and simulated AET values during 2003 and 2004 were respectively about 0.54 and 0.71 mm per day. The basal crop coefficient (K-cb) value obtained for the olive orchard was similar in both seasons with an average of 0.54. This value was lower than that suggested by the FAO-56 (0.62). Similarly, the single approach of FAO-56 has been tested in the previous work (Er-Raki et al., 2008) over the same study site and it has been shown that this approach also simulates correctly AET when using the local crop coefficient and under no stress conditions. Since the dual approach predicts separately soil evaporation and plant transpiration, an attempt was made to compare the simulated components of AET with measurements obtained through a combination of eddy covariance and scaled-up sap flow measurements. The results showed that the model gives an acceptable estimate of plant transpiration and soil evaporation. The associated RMSE of plant transpiration and soil evaporation were 0.59 and 0.73 mm per day, respectively. Additionally, the irrigation efficiency was investigated by comparing the irrigation scheduling design used by the farmer to those recommended by the FAO model. It was found that although the amount of irrigation applied by the farmer (800 mm) during the growing season of olives was twice that recommended one by the FAO model (411 mm), the vegetation suffered from water stress during the summer. Such behaviour can be explained by inadequate distribution of irrigation. Consequently, the FAO model can be considered as a potentially useful tool for planning irrigation schedules on an operational basis.

Evaluation of irrigation scheduling program and spring wheat yield response in southwestern Colorado

Effective irrigation scheduling to manage water for spring wheat ( Triticum aestivum L.) in southwestern Colorado was investigated under variable water applications. This study was conducted (1) to determine the effects of varying rates of water replacement (0ET, 0.33ET, 0.67ET, 10ET, and 1.33ET) on spring wheat grain yield, dry matter yield, root water uptake, and water use efficiency, (2) to develop local crop coefficients, and (3) to evaluate the irrigation scheduling program called ‘SCHED’ that had been used in the area. Daily weather data was used to calculate reference ET using the Penman equation. Crop ET was predicted by using the irrigation scheduling program, ‘SCHED’. Both grain yield and dry matter increased significantly with the increase in water application rates, up to LOET application rate. Crop coefficients estimated at various water application rates were greater than the values used in the irrigation scheduling program. Total water use efficiency (TWUE) and irrigation water use efficiency (IWUE) for grain yield were considerably greater at 0.33ET than for other rates, whereas TWUE and IWUE for dry matter yield followed the order 0.33ET > LOET > 0.67ET > 1.33ET > 0ET.