Variable Rate Irrigation System Research Articles

Toward automated irrigation management with integrated crop water stress index and spatial soil water balance

AbstractDecision support systems intended for precision irrigation aim at reducing irrigation applications while optimizing crop yield to achieve maximum crop water productivity (CWP). These systems incorporate on-site sensor data, remote sensing inputs, and advanced algorithms with spatial and temporal characteristics to compute precise crop water needs. The availability of variable rate irrigation (VRI) systems enables irrigation applications at a sub-field scale. The combination of an appropriate VRI system along with a precise decision support system would be ideal for improved CWP. The objective of this study was to compare and evaluate two decision support systems in terms of seasonal applied irrigation, crop yield, and CWP. This study implemented the Spatial EvapoTranspiration Modeling Interface (SETMI) model and the Irrigation Scheduling Supervisory Control and Data Acquisition (ISSCADA) system for management of a center pivot irrigation system in a 58-ha maize-soybean field during the 2020 and 2021 growing seasons. The irrigation scheduling methods included: ISSCADA plant feedback, ISSCADA hybrid, common practice, and SETMI. These methods were applied at irrigation levels of 0, 50, 100, and 150% of the full irrigation prescribed by the respective irrigation scheduling method. Data from infrared thermometers (IRTs), soil water sensors, weather stations, and satellites were used in the irrigation methods. Mean seasonal irrigation prescribed was different among the irrigation levels and methods for the 2 years. The ISSCADA plant feedback prescribed the least irrigation among the methods for majority of the cases. The common practice prescribed the largest seasonal irrigation depth among the methods for three crop-year cases. The maize yield in rainfed was found to be significantly lower than the irrigated levels in 2020 since 2020 was a dry year. No significant differences were observed in crop yield among the different irrigation methods for both years. The CWP among the different irrigation methods ranged between 2.72 and 3.15 kg m−3 for 2020 maize, 1.03 and 1.13 kg m−3 for 2020 soybean, 3.57 and 4.24 kg m−3 for 2021 maize, and 1.19 and 1.48 kg m−3 for 2021 soybean. Deficit level (50%) had the largest irrigation water productivity in all crop-year cases in this study. The ISSCADA and SETMI systems were found to reduce irrigation applications as compared to the common practice while maintaining crop yield. This study was the first to implement the newly developed integrated crop water stress index (iCWSI) thresholds and the ISSCADA system for site-specific irrigation of maize and soybean in Nebraska.

Irrigation Zone Delineation and Management with a Field-Scale Variable Rate Irrigation System in Winter Wheat

Understanding spatial and temporal dynamics of soil water within fields is critical for effective variable rate irrigation (VRI) management. The objectives of this study were to develop VRI zones, manage irrigation rates within VRI zones, and examine temporal differences in soil volumetric water content (VWC) from irrigation events via soil sensors across zones. Five irrigation zones were delineated after two years (2016 and 2017) of yield and evapotranspiration (ET) data collection. Soil sensors were placed within each zone to give real time data of VWC values and assist in irrigation decisions within a 23 ha field of winter wheat (Triticum aestivum ‘UI Magic’) near Grace, Idaho, USA (2019). Cumulative irrigation rates among zones ranged from 236 to 298 mm. Although a statistical comparison could not be made, the irrigation rates were 0.6 to 21% less than an estimated uniform grower standard practice (GSP) irrigation approach. Based on soil sensor data, crop water stress was avoided with VRI management in all but Zone 3. Thus, this simple approach to VRI zone delineation and VWC monitoring has the potential to reduce irrigation, such as this study, on average by 12% and should be evaluated in other site-years to assess its viability.

Combined traffic control of irrigation on heterogeneous field

In arid areas, such as Hungary, most climate models forecast a rise in water scarcity. Irrigated land accounts for 2% of agricultural land in Hungary, with most irrigation technology being relatively outdated. The aim of this research was to lay the foundation for a combined traffic management system for a water-saving precision irrigation system on an 85-ha field in the Tisza River basin's reference region. High-precision soil maps were created to support the water-efficient variable-rate irrigation system by selecting and selecting areas for different agrotechnical implementations and precision farming zones.

Evaluating different metrics from the thermal-based two-source energy balance model for monitoring grapevine water stress

Precision irrigation management requires operational monitoring of crop water status. However, there is still some controversy on how to account for crop water stress. To address this question, several physiological, several physiological metrics have been proposed, such as the leaf/stem water potentials, stomatal conductance, or sap flow. On the other hand, thermal remote sensing has been shown to be a promising tool for efficiently evaluating crop stress at adequate spatial and temporal scales, via the Crop Water Stress Index (CWSI), one of the most common indices used for assessing plant stress. CWSI relates the actual crop evapotranspiration ET (related to the canopy radiometric temperature) to the potential ET (or minimum crop temperature). However, remotely sensed surface temperature from satellite sensors includes a mixture of plant canopy and soil/substrate temperatures, while what is required for accurate crop stress detection is more related to canopy metrics, such as transpiration, as the latter one avoids the influence of soil/substrate in determining crop water status or stress. The Two-Source Energy Balance (TSEB) model is one of the most widely used and robust evapotranspiration model for remote sensing. It has the capability of partitioning ET into the crop transpiration and soil evaporation components, which is required for accurate crop water stress estimates. This study aims at evaluating different TSEB metrics related to its retrievals of actual ET, transpiration and stomatal conductance, to track crop water stress in a vineyard in California, part of the GRAPEX experiment. Four eddy covariance towers were deployed in a Variable Rate Irrigation system in a Merlot vineyard that was subject to different stress periods. In addition, root-zone soil moisture, stomatal conductance and leaf/stem water potential were collected as proxy for in situ crop water stress. Results showed that the most robust variable for tracking water stress was the TSEB derived leaf stomatal conductance, with the strongest correlation with both the measured root-zone soil moisture and stomatal conductance gas exchange measurements. In addition, these metrics showed a better ability in tracking stress when the observations are taken early after noon.

Using NDVI for Variable Rate Cotton Irrigation Prescriptions

HighlightsCrop coefficients (Kcb) were calculated using Normalized Difference Vegetative Indices (NDVI) and compared to the FAO-56 method.Cotton yields using NDVI-Kcb based irrigation scheduling to a uniform checkbook irrigation were compared.Irrigated cotton yields were not significantly different between irrigation methods but were significantly higher in years requiring higher volumes of irrigation water.Cotton fiber quality was not significantly different for the two irrigation methods or plant populations.Abstract. Irrigation timing is crucial for achieving high cotton yields and lint quality. This irrigation timing is more challenging in the southeastern U.S. Coastal Plain region due to its spatial variable sandy soils with low water and nutrient holding capacities and rainfall variability during the growing season. To address these challenges, we conducted a 2-year (2017 and 2018) study evaluating two irrigation scheduling methods under a variable rate irrigation system. The two irrigation methods were: (1) a uniform irrigation management based on weekly crop water usage, and (2) spatial crop coefficients derived from normalized difference vegetative indices (NDVI). We compared cotton yields and water use efficiency using the two irrigation scheduling methods at two different planting densities. The two plant populations were 5 and 11.5 plants m2 to provide different NDVI readings and water requirements. In 2017, there were no significant differences in cotton yields due to the adequate rainfall during the growing season that required only three irrigations events. The mean irrigation depth for the NDVI method was significantly lower than the uniform method (56 and 64 mm, respectively, LSD = 4.2). In 2018, there was lower rainfall during the growing season requiring eight irrigation events and the cotton yields in the two irrigation treatments were significantly higher than the rainfed treatment. Irrigation depths in 2018 were not significantly different for the two irrigation methods. Water use efficiencies were not significantly different for the two irrigation methods. The planting density had little impact on the cotton yields, irrigation depth, water use efficiency, or cotton fiber quality. These results indicate that the NDVI-derived crop coefficient values were as effective in prescribing irrigation applications as the uniform irrigation method for irrigation management. The NDVI-derived crop coefficient irrigation method appears to be a useful tool for managing irrigation and developing irrigation prescriptions. Keywords: Cotton, Irrigation scheduling, Normalized difference vegetation indices, Variable rate irrigation

Assessing water distribution characteristics of a variable-rate irrigation system

Variable-rate irrigation (VRI) can effectively improve the irrigation efficiency. In this study, we evaluated the two key indicators, irrigation uniformity and accuracy for a three-span center pivot VRI system with the combination of two sprinkler types, i.e., the Nelson D3000 (a fixed spray plate sprinkler, FSPS) and the R3000 (a rotating spray plate sprinkler, RSPS), two sets of irrigation depths designed for four management zones (zones 1–4) of 10, 8, 15, and 20 mm and 10, 15, 20, and 25 mm, and three cycle times (CTs) of the solenoid valve of 30, 45, and 60 s, with constant-rate irrigation (CRI) as a reference. In addition, the radially affected lengths of irrigation depths in zones 1–4 under various VRI treatments were further determined. The radial (mean CUH = 90.8%) and circumferential application uniformity (mean CUH = 95.6%) as well as radial irrigation accuracy (mean NRMSE = 15.3%) of the R3000 were superior to those of D3000 under VRI. The irrigation uniformity and accuracy of each management zone were less impacted by the designed irrigation depth and CT, but more affected by the location of the management zone. The irrigation uniformity and accuracy of VRI were close to those of CRI, indicating that the VRI system tested could guarantee the same application performance as the CRI system. Changing the D3000 sprinklers to R3000 sprinklers in the VRI system effectively reduced the radially affected lengths of management zones. The radially affected lengths of D3000 under various treatments were primarily distributed from 3–6 m, whereas those of R3000 were 0–3 m. Thus, it was recommended to select RSPSs in the design of the center pivot VRI system, and the transition zone and CT in relation to R3000 sprinklers were suggested to be 0–3 m and 60 s, respectively. This research provides the recommendations for better implementation of VRI.

Effects of irrigation strategies and soil properties on the characteristics of deep percolation and crop water requirements for a variable rate irrigation system

Reducing deep percolation (DP) across the field is one of the main objectives of a variable rate irrigation (VRI) system under a semi-humid climate. A study was conducted in the North China Plain during the 2016 and 2017 maize growing seasons in a 1.64-ha one-quadrant plot irrigated by a VRI centre pivot irrigation system. The study was designed to quantify and compare the DP dynamics of three irrigation strategies, including soil water balance (SWB), measured soil water content (SWC), and a combination of SWB and rain forecasting for the next three days (RF). The area irrigated by the VRI system was delineated into three management zones (zones 1, 2, and 3) based on the available soil water holding capacity (AWC). Based on the seasonal cumulative DP, the zone-specific crop coefficient (Kc) for each zone was quantified to enhance the accuracy of the SWB method. The results indicated that high daily DP rates occurred during the initial and end growing seasons as well as following rainfall and irrigation events during the mid-season. The delay of DP after an intermittent large rainfall was observed in both seasons. The cumulative DP in zone 2 with a medium AWC and a uniform soil profile was 36% less than the mean values of DP for zones 1 and 3. Compared to the SWC and SWB methods, the cumulative DP for the RF treatment was reduced by 10% and 36%, respectively. During both seasons, the maximum DP values were observed in zones 2 and 3 under the SWB methods. The SWC method tended to increase the risk of DP for a coarse profile, whereas a lower sandy content soil tended to increase the risk for the SWB method. The mean Kc values derived based on DP for the initial, mid-season, and end of the late season stages were 0.86, 0.73, and 0.91 for zones 1, 2, and 3, respectively, with a 7% reduction compared to the Kc without considering DP. The seasonal crop water requirement determined by zone-specific Kc was reduced by 31 mm compared with the uniform Kc in different management zones. Our results suggested that the RF method exhibited promise for reducing DP, and the zone-specific Kc values were helpful to enhance the water savings of the SWB method for a VRI system.

A new approach for estimating and delineating within-field crop water stress zones with satellite imagery

ABSTRACT As water scarcity and demand for food both grow, viable solutions to efficiently irrigate crops are needed. The recent advent of variable rate irrigation systems provides technology for growers to water their fields accounting for the spatially heterogeneous demand of their crops for water. Some zones within a field may require less or more water based on varying solar radiation, soil type, or surface or subsurface water flow paths. Since these processes are heterogeneous and complex, they are challenging to model or measure with the spatial resolution necessary to implement successful variable rate irrigation. In this paper, we present a new approach that uses high-resolution (20 to 100 m) satellite imagery obtained from Sentinel-2 and Landsat 8 to estimate zones of crop water stress. Our approach integrates two independent measures of crop water availability – Normalized Difference Water Index, and Evapotranspiration modelled using remotely sensed land surface temperature – with k-means clustering to delineate zones in an automated fashion. Our study area in southern Idaho has been set up experimentally to grow crops that are water-stressed and not water-stressed, thus providing a rigorous design to test and validate our method. The results of our method agree well with our independent suite of crop water stress measures, such as yield, variable irrigation rates, and matric potential. This method can be used to develop data-driven zones for variable rate irrigation, which has the potential to improve the efficiency of water use without sacrificing yield.

Imaging the electrical conductivity of the soil profile and its relationships to soil water patterns and drainage characteristics

Soil water content (θ) measurement is vital for accurate irrigation scheduling. Electromagnetic induction surveys can be used to map spatial variability of θ when other soil properties are uniform. However, depth-specific θ variations, essential for precision irrigation management, have been less investigated using this method. A quasi-2-dimensional inversion model, capable of inverting apparent soil electrical conductivity (ECa) data to calculate estimates of true electrical conductivity (σ) down the entire soil profile, was developed using ECa data collected by a multi-coil Dualem-421S sensor. The optimal relationships between σ and volumetric water content (θv) were established using all coil arrays of the Dualem-421S, a damping factor of 0.04, an initial model of 35 mSm−1, and with ten iterations (R2 = 0.70, bias = 0.00 cm3cm−3, RMSE = 0.04 cm3cm−3). These relationships were then used to derive soil profile images of these properties, and as expected, θv and σ follow similar trends down the soil profile. The derived soil profile images for θv have potential use for irrigation scheduling to two ECa-derived soil management zones under a variable rate irrigation system at this case study site. They reflect the intrinsic soil differences that occur between texture, texture transitions and drainage characteristics. The method can also be used to guide placement of soil moisture sensors for in-season monitoring of spatio-temporal variations of θv. This soil imaging method showed good potential for predicting 2D depth profiles of soil texture, moisture and drainage characteristics, and supporting soil, plant and irrigation management.

Development and Evaluation of a Variable-Rate Irrigation Management Method in the Mississippi Delta

HighlightsWe developed and evaluated a variable-rate irrigation (VRI) management method for five crop years in the Mississippi Delta.VRI management significantly reduced irrigation water use in comparison with uniform-rate irrigation (URI). There was no significant difference in grain yield and irrigation water productivity between VRI and URI management.Soil apparent electrical conductivity (ECa) was used to delineate irrigation management zones and generate VRI prescriptions.Sensor-measured soil water content was used in irrigation scheduling.Abstract. Variable-rate irrigation (VRI) allows producers to site-specifically apply irrigation water at variable rates within a field to account for the temporal and spatial variability in soil and plant characteristics. Developing practical VRI methods and documenting the benefits of VRI application are critical to accelerate the adoption of VRI technologies. Using apparent soil electrical conductivity (ECa) and soil moisture sensors, a VRI method was developed and evaluated with corn and soybean for five crop years in the Mississippi Delta. Soil ECa of the study fields was mapped and used to delineate VRI management zones and create VRI prescriptions. Irrigation was scheduled using soil volumetric water content measured by soil moisture sensors. A center pivot VRI system was employed to deliver irrigation water according to the VRI prescription. Grain yield, irrigation water use, and irrigation water productivity in the VRI treatment were determined and compared with that in a uniform-rate irrigation (URI) treatment. Results showed that the grain yield and irrigation water productivity between the VRI and URI treatments were not statistically different with both corn and soybean crops. The VRI management significantly reduced the amount of irrigation water by 22% in corn and by 11% in soybean (p = 0.05). Adoption of VRI management could improve irrigation water use efficiency in the Mississippi Delta. Keywords: Soil electrical conductivity, Soil moisture sensor, Variable rate irrigation, Water management.

A Variable-Rate Irrigation Decision Support System for Corn in the U.S. Eastern Coastal Plain

HighlightsA decision support system using the USDA-ARS Irrigation Scheduling and Supervisory Control and Data Acquisition (ISSCADA) system was evaluated for spatially managing corn irrigation in the U.S. Eastern Coastal Plain.The ISSCADA system was compared to traditional scheduling methods based on measured soil water potentials.The ISSCADA system with feedback on allowable soil water depletion shows potential as a tool for growers for managing variable-rate irrigation systems.Abstract. Variable-rate irrigation (VRI) systems are capable of applying different water depths both in the direction of travel and along the length of the irrigation system. VRI systems maybe useful for improving crop water management and efficiency. Although VRI technology is available and has high grower interest, it has had limited adoption. To address this, researchers have developed a decision support system that uses remote sensing of plant, soil, and microclimate to schedule VRI irrigations. In this research, we evaluated the use of the USDA-ARS Irrigation Scheduling and Supervisory Control and Data Acquisition (ISSCADA) system for spatially managing corn irrigation in the U.S. Eastern Coastal Plain. The ISSCADA system consists of center pivot mounted infrared thermometers (IRT) to measure crop canopy temperatures and in situ soil water sensors. An integrated crop water stress index (iCWSI) was calculated from the canopy temperatures. The ISSCADA system analyzes the iCWSI and soil water measurements to provide an irrigation recommendation. The ISSCADA system was evaluated using (1) iCWSI values and (2) a hybrid ISSCADA system that incorporated both iCWSI values and soil water depletion criteria. These ISSCADA treatments were compared to traditional irrigation management using measured soil water potentials. The ISSCADA system was evaluated for four years. In 2016 and 2017, corn yields and water use efficiency were not significantly different between the irrigation treatments due to adequate rainfall during the growing season. In 2018 and 2019, mid-season drought conditions and sporadic rainfall patterns required frequent irrigations. In both years, the irrigation treatment corn yields were not significantly different from each other but were greater than the rainfed yields. In 2018, the irrigation treatments produced corn yields of 10.7, 10.4, and 10.1 Mg ha-1 for the hybrid, ISSCADA, and SWP treatments, respectively. Over the four-year study, the water use efficiencies of the irrigation treatments were not significantly different from each other or the rainfed treatment and ranged from 16.6 to 22.7 kg ha-1 mm-1. In the two years that the hybrid ISSCADA system was used for managing irrigations, it produced higher corn yields and required less irrigation than the standard ISSCADA treatments. Results from this experiment will help to evaluate and refine the ISSCADA system to provide a tool for growers to use in managing spatial irrigation with VRI systems. Keywords: Crop water stress, Decision support system, Variable rate irrigation.

Assessing the Effectiveness of Variable-Rate Drip Irrigation on Water Use Efficiency in a Vineyard in Northern Italy

Although many studies in the literature illustrate the numerous devices and methodologies nowadays existing for assessing the spatial variability within agricultural fields, and indicate the potential for variable-rate irrigation (VRI) in vineyards, only very few works deal with the implementation of VRI systems to manage such heterogeneity, and these studies are usually conducted in experimental fields for research aims. In this study, a VR drip irrigation system was designed for a 1-ha productive vineyard in Northern Italy and managed during the agricultural season 2018, to demonstrate feasibility and effectiveness of a water supply differentiated according to the spatial variability detected in field. Electrical resistivity maps obtained by means of an electro-magnetic induction sensor were used to detect four homogeneous zones with similar soil properties. In each zone, a soil profile was opened, and soil samples were taken and analyzed in laboratory. Two irrigation management zones (MZs) were identified by grouping homogeneous zones on the basis of their hydrological properties, and an irrigation prescription map was built consistently with the total available water (TAW) content in the root zone of the two MZs. The designed drip irrigation system consisted of three independent sectors: the first two supplied water to the two MZs, while the third sector (reference sector) was managed following the farmer’s habits. During the season, irrigation in the first two sectors was fine-tuned using information provided by soil moisture probes installed in each sector. Results showed a reduction of water use by 18% compared to the ‘reference’ sector without losses in yield and product quality, and a grape’s maturation more homogeneous in time.

Maximizing water productivity of winter wheat by managing zones of variable rate irrigation at different deficit levels

To determine the specific application rate for each management zone of a variable rate irrigation system, the yield and water use efficiency (WUE) of winter wheat were evaluated during two growing seasons at different deficit levels in the alluvial flood plain of the North China Plain. One 1.64-ha quadrant irrigated by a variable rate center pivot system was delineated into four management zones with available soil water holding capacity, and varied soil profiles were detected in these zones. Each zone was divided into several subzones to be irrigated at different deficit levels. In the 2016 season, each subzone was managed individually with irrigation trigger points of 55%, 65%, 75%, and 80% of field capacity along with a rain-fed treatment. In the 2017 season, all subzones were irrigated simultaneously with 0%, 33%, 67%, 100%, and 120% of the base application depth. For the two-season study, the rain-fed treatment produced significantly lower yield and WUE than the irrigated treatments, and both the maximum yield and the maximum WUE were obtained in zone 2, where a more uniform soil profile was detected. A linear crop water production function was determined for zones 1 and 3 in the 2017 season, while a quadratic equation fit the crop water production function well for other zones in the two seasons. The relationship between WUE and crop water use in the three zones can be represented by a curvilinear equation for both seasons. Taking the optimal application rate of maximizing WUE in zone 1 as a basis, 89% and 94% of the rate in zone 1 was recommended for zones 2 and 3, respectively, to achieve the maximum WUE in the entire field. Our results also suggested that the existing layered-textural soil profile can greatly influence crop productivity and should therefore be considered in mapping irrigation prescriptions.

Fuzzy control system for variable rate irrigation using remote sensing

Variable rate irrigation (VRI) is the capacity to spatially vary the depth of water application in a field to handle different types of soils, crops, and other conditions. Precise management zones must be developed to efficiently apply variable rate technologies. However, there is no universal method to determine management zones. Using speed control maps for the central pivot is one option. Thus, this study aims to develop an intelligent fuzzy inference system based on precision irrigation knowledge, i.e., a system that can create prescriptive maps to control the rotation speed of the central pivot. Satellite images are used in this study because remote sensing offers quick measurements and easy access to information on crops for large irrigation areas. Based on the VRI-prescribed map created using the intelligent decision-making system, the pivot can increase or decrease its speed, reaching the desired depth of application in a certain irrigation zone. Therefore, considering the spatial variability in the crop has made the strategy of speed control more realistic than traditional methods for crop management. The intelligent irrigation system pointed out areas with lower leaf development, indicating that the pivot must reduce its speed, thus increasing the water layer applied to that area. The existence of well-divided zones could be observed; each zone provides a specific value for the speed that the pivot must develop for decreasing or increasing the application of the water layer to the crop area. Three quarters of the total crop area had spatial variations during water application. The set point built by the developed system pointed out zones with a decreased speed in the order of 50%. From the viewpoint of a traditional control, the relay from pivot percent timer should have been adjusted from 70% to 35% whenever the central pivot passed over that specific area. The proposed system obtained values of 37% and 47% to adjust the pivot percent timer. Therefore, it is possible to affirm that traditional control models used for central-pivot irrigators do not support the necessary precision to meet the demands of speed control determined by the developed VRI systems. Results indicate that data from the edaphoclimatic variables when well-fitted to the fuzzy logic can solve uncertainties and non-linearities of an irrigation system and establish a control model for high-precision irrigation.

Potential Water Conservation Using Site-Specific Variable Rate Irrigation

Abstract. Site-specific variable-rate irrigation (VRI) systems can be used to spatially manage irrigation within sub-field-sized zones and optimize spatial water use efficiency. The goal of the research is to provide farmers and consultants a tool to evaluate the potential benefits of implementing VRI. The specific objective of this research is to evaluate the potential water savings using VRI management compared with uniform irrigation management to maintain soil water holding capacity above 50% depletion using two irrigation scenarios: 1) a standard 12.5 mm irrigation per application; and 2) an application to refill the soil profile to field capacity. A 21-year simulation study was carried out on a selected field with varying degrees of soil and topographic variability. The simulated field had 12 soil mapping units with water holding capacities in the top 0.30-m ranging from 42 to 70 mm. The 21-year simulation covering all weather conditions for each soil produced only two significantly different irrigation management zones for scenario 1, and for scenario 2 only one management zone. However, when the 21-year period was divided into periods with different ratios of rainfall to reference evapotranspiration, the simulations identified 1 to 5 management zones with significantly different irrigation requirements. These results indicate that variable rate irrigation system design and management should not be solely based on long term average weather conditions. Years with differing weather conditions should be used for potentially identifying management zones for VRI systems. Irrigation application depths between management zones ranged from 17 to 38 mm. However, when the actual soil areas of the study field were utilized to calculate the total volume of irrigation water applied, it resulted in an increase in water usage in the 2 and 4 management zones ranging from -1.2% to 5.8%. Water usage with VRI over uniform irrigation was greater by -1.6% to 6.8% in the 12.5 mm irrigations and by -1.2% to 2.2% for the field capacity irrigations Keywords: Management zones, Precision farming, Variable-rate irrigation, Water conservation.

Center-Pivot-Mounted Sensing System for Monitoring Plant Height and Canopy Temperature

Abstract. Easy-to-use data acquisition methods are required for variable-rate irrigation (VRI) decision support systems. Plant canopy temperature is related to plant water stress. Plant height is useful as an indicator of plant health conditions and can be used to estimate yield potential. Therefore, measurements of plant canopy temperature and plant height coupled with spatial information in the field can be used for determining VRI water application depths. A center-pivot-mounted wireless data acquisition (WDAQ) system was developed to collect plant canopy temperature and plant height data in the field. Each WDAQ unit consisted of a GPS receiver, programmable data logger, infrared temperature sensor, ultrasonic distance sensor, solar power supply, and wireless data transmitter/receiver. The system included two WDAQ units installed on a four-span center-pivot VRI system. One unit was mounted at the middle of the third span, and the other was mounted at the middle of the fourth span from the pivot. The infrared temperature sensors were used to detect the canopy temperature, while the ultrasonic distance sensors were used to measure plant height. The WDAQ system was designed to continuously and simultaneously measure plant canopy temperature and plant height and record the spatial coordinates at each measurement location as the center pivot moved around the field. Data collected were wirelessly transferred to a receiver for data processing. This WDAQ system has been tested and evaluated in the field for two years. Test results indicated that the WDAQ system was able to record approximately 3,200 measurements from each sensor in one pivot circle (360°). The measurement error of the ultrasonic distance sensor was 0.2 to 3 cm in a measurement range of 14 to 209 cm, and the sensor-measured plant heights were strongly correlated with manually tape-measured plant heights in soybean and cotton crops (r2 = 0.97). Combined with the spatial information, measurements of plant height and crop canopy temperature were used to generate plant height and crop canopy temperature maps. Spatial variabilities of plant height and canopy temperature across the field could be identified from the maps and used in irrigation research. The WDAQ system has great potential for automatic creation of VRI prescription maps and plant-based irrigation scheduling. Keywords: Canopy temperature, Irrigation scheduling, Plant height, Sensors, Variable-rate irrigation.

Crop Yield and Water Use Efficiency as Affected by Different Soil-Based Management Methods for Variable-Rate Irrigation in a Semi-Humid Climate

Abstract. To improve the management of variable-rate irrigation (VRI) systems in semi-humid climates, three different soil-based irrigation management methods were evaluated on their potential for reducing irrigation water use and maximizing crop yield and water use efficiency (WUE) during the 2016 and 2017 growing seasons of summer maize in the North China Plain. The three irrigation management methods evaluated were soil water balance modeling (SWB), measured soil water content (SWC), and a combination of SWB and the rain forecast for the next three days (RF). The experiments were implemented on four management zones delineated by available soil water holding capacity of a center-pivot VRI system. A similar irrigation trigger point (70% of field capacity) was used for the three irrigation management methods in the four management zones. In the two seasons, the total water application in the SWC treatments varied in a larger range among the management zones, and the irrigation water applied was 22% and 21% less than in the SWB and RF treatments, respectively. Similar yields were obtained among the irrigation management methods in both seasons. The maximum WUE was always observed with the SWC treatments for the four management zones in the 2017 season. The WUE with the SWC treatments was 36% and 23% higher than with the SWB and RF treatments, respectively. Considering the amount of irrigation water applied, yield, and WUE, our results demonstrated that the SWC method was more suitable for VRI management than the SWB and RF methods in this semi-humid climate. Keywords: Center pivot, Soil water balance, Soil water content, Rain forecast, Summer maize, Yield.

Determining placement criteria of moisture sensors through temporal stability analysis of soil water contents for a variable rate irrigation system

Developing placement criteria for soil moisture sensors is crucial in increasing the practical functionality of a variable rate irrigation (VRI) system. In this field study, the temporal stability pattern of soil water content was compared between VRI and uniform rate irrigation (URI) treatments during growing seasons of winter wheat and summer maize to determine the placement criteria of soil water sensors. The 1.64-ha experimental site located in a highly variable alluvial flood plain was divided into four management zones according to the available water holding capacity ranging from 152 to 205 mm within the 0.6 m soil profile. In each zone, two sub-zones were created to represent VRI and URI treatments. A temporal stability analysis of soil moisture was conducted by regularly measuring soil water contents at 62 locations in the field during the growing seasons. Results showed that the VRI management changed the overall similarity of soil moisture spatial patterns when crop water consumption was provided mainly by irrigation water rather than precipitation. In each management zone, every measuring position was a time-stable location with respect to the mean soil water content. Significant linear regressions were detected between the mean clay percentile in each management zone and the clay percentile representing the mean soil water content sites, and a nearly equivalent value of fitted equation coefficient was obtained for winter wheat (1.15) and summer maize (1.19). These results demonstrated that the temporal stability of soil water content spatial patterns still existed in each management zone with the VRI management, and the clay percentile supplied a priori identification for placement of soil moisture sensors.

Field Study of Variable Rate Irrigation Management in Humid Climates

AbstractComparison of variable rate irrigation (VRI) management with uniform rate irrigation (URI) management in soybean and corn crops was studied for 2 years in Stoneville, Mississippi, USA. The experiments were conducted on two 6.7 ha fields. Each of them was equally split into two sectors. VRI management was performed in one sector and URI management in the other. A centre pivot VRI system was used for delivering irrigation water. Soil apparent electrical conductivity (EC) of the fields was used to delineate VRI management zones and create a VRI prescription map. The VRI treatment used 25% less irrigation water and produced 2.8% more yield in soybean and 0.8% more yield in corn than the URI treatment. Irrigation water productivity (WP) of soybean under VRI management was 0.84 kg m−3 which is 31.2% higher than URI. The WP of corn under VRI management was 1.69 kg m−3, 27.1% higher than URI. Yield of the rainfed treatment was significantly lower than the VRI and URI treatments for both soybean and corn in the 2015 season (p < 0.05). Results in this study demonstrated that VRI management was superior to URI in terms of water use efficiency. Copyright © 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA. Copyright © 2017. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Infrared thermometry to quantify in-field soil moisture variability

ABSTRACTTechniques to formulate accurate and timely prescriptions for variable-rate irrigation systems lag behind the hardware capabilities. Canopy temperature measurements could serve as an indicator of water stress, but current methods that exploit the data can be cumbersome. The objectives of this study were 1) to determine the relationship between synchronous measurements of maize (Zea mays L.) canopy temperature and in-field soil moisture tension, and 2) to understand the influence of discretionary crop canopy temperature stress thresholds on the relationship between soil moisture tension and crop canopy temperature. A variable-rate irrigation pivot was used to form six water-treatment zones. Each zone was equipped with tensiometers installed in the center of the plots and an infrared thermometer pointed into the crop canopy to individually monitor conditions in each zone. Results of this study indicate that synchronous canopy temperature was able to quantify soil moisture tension, particularly during the reproductive crop growth stages. Using inexpensive infrared thermometers with this method could provide a cost-effective solution for gauging in-field soil moisture variability.