EXPLORING SPATIAL AND TEMPORAL VARIABILITY OF SOIL AND CROP PROCESSES FOR IRRIGATION MANAGEMENT

Irrigation needs to be applied to soils in relatively humid regions such as western Kentucky to supply water for crop uptake to optimize and stabilize yields. Characterization of soil and crop variability at the field scale is needed to apply site specific management and to optimize water application. The objective of this work is to propose a characterization and modeling of soil and crop processes to improve irrigation management. Through an analysis of spatial and temporal behavior of soil and crop variables the variability in the field was identified. Integrative analysis of soil, crop, proximal and remote sensing data was utilized. A set of direct and indirect measurements that included soil texture, electrical conductivity (EC), soil chemical properties (pH, organic matter, N, P, K, Ca, Mg and Zn), NDVI, topographic variables, were measured in a silty loam soil near Princeton, Kentucky. Maps of measured properties were developed using kriging, and cokriging. Different approaches and two cluster methods (FANNY and CLARA) with selected variables were applied to identify management zones. Optimal scenarios were achieved with dividing the entire field into 2 or 3 areas. Spatial variability in the field is strongly influenced by topography and clay content. Using Root Zone Water Quality Model 2.0 (RZWQM), soil water tension was modeled and predicted at different zones based on the previous delineated zones. Soil water tension was measured at three depths (20, 40 and 60 cm) during different seasons (20016 and 2017) under wheat and corn. Temporal variations in soil water were driven mainly by precipitation but the behavior is different among management zones. The zone with higher clay content tends to dry out faster between rainfall events and reveals higher fluctuations in water tension even at greater depth. The other zones are more stable at the lower depth and share more similarities in their cyclic patterns. The model predictions were satisfactory in the surface layer but the accuracy decreased in deeper layers. A study of clay mineralogy was performed to explore field spatial differences based on the map classification. kaolinite, vermiculite, HIV and smectite are among the identified minerals. The clayey area presents higher quantity of some of the clay minerals. All these results show the ability to identify and characterize the field spatial variability, combining easily obtainable data under realistic farm conditions. This information can be utilized to manage resources more effectively through site specific application

Identifying Advantages and Disadvantages of Variable Rate Irrigation – An Updated Review

Variable rate irrigation (VRI) sprinklers on mechanical move irrigation systems (center pivot or lateral move) have been commercially available since 2004. Although the number of VRI, zone or individual sprinkler, systems adopted to date is lower than expected there is a continued interest to harness this technology, especially when climate variability, regulatory nutrient management, water conservation policies, and declining water for agriculture compound the challenges involved for irrigated crop production. This article reviews the potential advantages and potential disadvantages of VRI technology for moving sprinklers, provides updated examples on such aspects, suggests a protocol for designing and implementing VRI technology and reports on the recent advancements. The advantages of VRI technology are demonstrated in the areas of agronomic improvement, greater economic returns, environmental protection and risk management, while the main drawbacks to VRI technology include the complexity to successfully implement the technology and the lack of evidence that it assures better performance in net profit or water savings. Although advances have been made in VRI technologies, its penetration into the market will continue to depend on tangible and perceived benefits by producers

New sensing methods for scheduling variable rate irrigation to improve water use efficiency and reduce the environmental footprint : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand

Figures are re-used under an Attribution 4.0 International (CC BY 4.0) license, or are not copyrighted.Irrigation is the largest user of allocated freshwater, so conservation of water use should begin with improving the efficiency of crop irrigation. Improved irrigation management is necessary for humid areas such as New Zealand in order to produce greater yields, overcome excessive irrigation and eliminate nitrogen losses due to accelerated leaching and/or denitrification. The impact of two different climatic regimes (Hawkes Bay, Manawatū) and soils (free and imperfect drainage) on irrigated pea (Pisum sativum., cv. ‘Ashton’) and barley (Hordeum vulgare., cv. ‘Carfields CKS1’) production was investigated. These experiments were conducted to determine whether variable-rate irrigation (VRI) was warranted. The results showed that both weather conditions and within-field soil variability had a significant effect on the irrigated pea and barley crops (pea yield - 4.15 and 1.75 t/ha; barley yield - 4.0 and 10.3 t/ha for freely and imperfectly drained soils, respectively). Given these results, soil spatial variability was characterised at precision scales using proximal sensor survey systems: to inform precision irrigation practice. Apparent soil electrical conductivity (ECa) data were collected by a Dualem-421S electromagnetic (EM) survey, and the data were kriged into a map and modelled to predict ECa to depth. The ECa depth models were related to soil moisture (θv), and the intrinsic soil differences. The method was used to guide the placement of soil moisture sensors. After quantifying precision irrigation management zones using EM technology, dynamic irrigation scheduling for a VRI system was used to efficiently irrigate a pea crop (Pisum sativum., cv. ‘Massey’) and a French bean crop (Phaseolus vulgaris., cv. ‘Contender’) over one season at the Manawatū site. The effects of two VRI scheduling methods using (i) a soil water balance model and (ii) sensors, were compared. The sensor-based technique irrigated 23–45% less water because the model-based approach overestimated drainage for the slower draining soil. There were no significant crop growth and yield differences between the two approaches, and water use efficiency (WUE) was higher under the scheduling regime based on sensors. ii To further investigate the use of sensor-based scheduling, a new method was developed to assess crop height and biomass for pea, bean and barley crops at high field resolution (0.01 m) using ground-based LiDAR (Light Detection and Ranging) data. The LiDAR multi-temporal, crop height maps can usefully improve crop coefficient estimates in soil water balance models. The results were validated against manually measured plant parameters. A critical component of soil water balance models, and of major importance for irrigation scheduling, is the estimation of crop evapotranspiration (ETc) which traditionally relies on regional climate data and default crop factors based on the day of planting. Therefore, the potential of a simpler, site-specific method for estimation of ETc using in-field crop sensors was investigated. Crop indices (NDVI, and canopy surface temperature, Tc) together with site-specific climate data were used to estimate daily crop water use at the Manawatū and Hawkes Bay sites (2017-2019). These site-specific estimates of daily crop water use were then used to evaluate a calibrated FAO-56 Penman-Monteith algorithm to estimate ETc from barley, pea and bean crops. The modified ETc–model showed a high linear correlation between measured and modelled daily ETc for barley, pea, and bean crops. This indicates the potential value of in-field crop sensing for estimating site-specific values of ETc. A model-based, decision support software system (VRI–DSS) that automates irrigation scheduling to variable soils and multiple crops was then tested at both the Manawatū and Hawkes Bay farm sites. The results showed that the virtual climate forecast models used for this study provided an adequate prediction of evapotranspiration but over predicted rainfall. However, when local data was used with the VRI–DSS system to simulate results, the soil moisture deficit showed good agreement with weekly neutron probe readings. The use of model system-based irrigation scheduling allowed two-thirds of the irrigation water to be saved for the high available water content (AWC) soil. During the season 2018 – 2019, the VRI–DSS was again used to evaluate the level of available soil water (threshold) at which irrigation should be applied to increase WUE and crop water productivity (WP) for spring wheat (Triticum aestivum L., cv. ‘Sensas’) on the sandy loam and silt loam soil zones at the Manawatū site. Two irrigation thresholds (40% and 60% AWC), were investigated in each soil zone along with a rainfed control. Soil water uptake pattern was affected mainly by the soil type rather than irrigation. The soil iii water uptake decreased with soil depth for the sandy loam whereas water was taken up uniformly from all depths of the silt loam. The 60% AWC treatments had greater irrigation water use efficiency (IWUE) than the 40% AWC treatments, indicating that irrigation scheduling using a 60% AWC trigger could be recommended for this soil-crop scenario. Overall, in this study, we have developed new sensor-based methods that can support improved spatial irrigation water management. The findings from this study led to a more beneficial use of agricultural water

Automatic Irrigation Scheduling on a Hedgerow Olive Orchard Using an Algorithm of Water Balance Readjusted with Soil Moisture Sensors

Recent technological advances have made possible automated irrigation scheduling using decision-support tools. These tools help farmers to make better decisions in the management of their irrigation system, thus increasing yields while preserving water resources. The aim of this study is to evaluate in a commercial plot an automated irrigation system combined with remote-sensing techniques and soil mapping that allows the establishment of regulated deficit irrigation (RDI) strategies. The study was carried out over 3 years (2015–2017) in a commercial hedgerow olive orchard of the variety ‘Arbequina’ located in Alvarado (Extremadura, Spain). An apparent electrical conductivity (ECa) map and a normalized difference vegetation index (NDVI) map were generated to characterize the spatial variability of the plot and classify the zones in homogeneous areas. Then, reference points were selected to monitor the different irrigation sectors. In 2015, the plot was irrigated according to the farmer’s technical criteria throughout the plot. In 2016 and 2017, two different areas of the plot were irrigated applying an RDI strategy, one under expert supervision and the other automatically. The results show that in a heterogeneous plot the use of new technologies can be useful to establish the ideal location for an automatic irrigation system. Furthermore, automatic irrigation scheduling made it possible to establish an RDI strategy recommended by an expert, resulting in the homogenization of production throughout the plot without the need for human intervention.info:eu-repo/semantics/publishedVersio

Groundwater Recharge Response to Reduced Irrigation Pumping in Western Nebraska

Given current and continued investment in irrigation scheduling technologies, a need exists to better estimate the longevity and magnitude of water savings at watershed level to avoid the paradox of irrigation efficiency. This paradox occurs within a watershed as not all irrigation inefficiencies lead to the system losing water. For example, irrigation pumping rates in excess of crop water demand may lead to enhanced groundwater recharge or surface runoff that migrates to a stream. Thus, increases in efficiency may not lead to similar magnitudes of water savings. I hypothesize that water savings longevities are short given previous work demonstrating rapid responses of groundwater recharge rates to changing surface conditions. To test this hypothesis, I used numerical modeling and hydrogeological field techniques. This work provides localized ranges of: weather, management, soil variability, depth to groundwater, and water fluxes. In chapter two, utilizing a crop modeling and numerical modeling of soil moisture redistribution, I found that irrigation practices within the study area could be reduced by 120 mm yr-1 with impact on yield less than 3% when compared to a long-term dataset of irrigation pumping rates for ~50 fields within the study area. From work in chapter three, I found that sampling locations informed via repeat hydrogeophysical surveys, required only five cores to reduce the cross-validation root mean squared error by an average of 64% as compared to soil parameters predicted by a commonly used benchmark, SSURGO and ROSETTA. This work then informed an intermediate core sampling framework in chapter four to constrain how soil hydraulic fluxes vary on subfield scale. In chapter four, I compared deep drainage outputs of a numerical model parameterized with localized measurements to a chemical tracer analysis and find agreement within 80% despite a wide range of fluxes observed (135-515mm yr-1). Scenario testing informed using the parameterized numerical model and the irrigation reduction potential from chapter two indicated that a 120mm yr-1 reduction of pumping leads to modest water savings (1-3 years; 50-200mm over 10 years). However, when applied over a number of fields, similar irrigation efficiency programs may be competitive with other water resource management programs. Adviser: Trenton E. Fran

Addressing Data Resolution in Precision Agriculture

Irrigated agriculture constitutes the greatest consumptive water use globally, so that irrigation efficiency measures are an important part of global efforts to best utilize this limited resource. However, greater irrigation efficiency must be achieved while simultaneously maintaining or increasing crop yields and farming profitability. Incremental water use decisions are made at the local level by farmers under many real world constraints; consequently they face significant risks in operating large and complex irrigation systems. These decisions should be supported by reliable information upon which to base operational plans and irrigation scheduling. Implementing precision irrigation effectively depends upon highly resolved estimates of crop water demand so that application rates match demand precisely both in location and timing. A fundamental challenge in mapping the irrigation requirement is addressing the heterogeneity of soil, biophysical, and atmospheric processes which mediate water demand. However, existing methods to determine the irrigation requirement assume that field conditions are homogeneous. Precision irrigation systems may enable more specific water distribution than traditional irrigation equipment, but allocating the correct amount of water requires crop water estimates that accurately reflect the variability of the irrigation requirement and consider the scale and timing at which irrigation can be delivered. This dissertation synthesizes the results from field studies which analyzed spatial patterns of irrigation performance and crop water demand under real field conditions. The first experiment quantified the performance of a precision irrigation system and determined the data resolution required for effective utilization of the system’s capability (Chapter 2). Field trials were conducted with a variable rate center pivot sprinkler (VRI) under normal farming conditions to determine this spatial resolution. The result was the definition of a performance coefficient and characteristic length scale associated with the irrigation system. The characteristic length scale describes the highest resolution prescription possible with VRI. Following on these findings, a second study compares an electromagnetic (EM) soil mapping method using extensive laboratory soil characterization as a basis for comparison (Chapter 3). The motivation of the study was to validate the EM method’s capability to detect small scale variations in soil water holding capacity, and to determine under which conditions the EM method can obtain reliable and robust soil maps. The findings reinforce earlier work on the importance of instrument calibration, and also show that specific soil characteristics may preclude using EM methods to map soil in some regions. Following the soil mapping study, further studies investigated methods to measure crop evapotranspiration (ET). A literature review was conducted to establish a catalog of contemporary methods to monitor ET, focusing on those commonly used in agriculture (Chapter 4). From this review, the surface renewal method (SR) emerged as potentially able to map ET feasibly and cost-effectively. Four field experiments were conducted over two years under a range of field conditions to establish a robust protocol for the determination of surface fluxes with SR (Chapter 5). Three of these experiments specifically investigated the potential for SR to be implemented from a moving sensor platform, such as an unmanned aerial vehicle. Experiments showed SR could estimate sensible heat flux as accurately as eddy covariance during moving trials. However, analysis of the minimum flux averaging period demonstrated that SR cannot resolve fluxes at the requisite spatial scales for precision irrigation. Nonetheless, SR remains promising for other practical applications in measuring surface fluxes. Future research questions and potential applications are explored in Chapters 5 and 6. The methods described here are directly relevant to water managers at the levels of farms and irrigation districts. Efficient irrigation planning depends on timely, reliable, and site-specific information in order to anticipate crop water demand, irrigate adequately to prevent drought stress, and maximize yield from the available resource. Growers and irrigation specialists currently have many resources at their disposal, including regional and satellite based ET estimates, state and local soil mapping, and scientific irrigation planning software. However, these methods do not provide site-specific and real time measurements of actual crop water demand, and farmers do not have any reliable means by which to validate the accuracy and precision of these estimates. For this information to be directly useful in irrigation planning, it should be validated by on site measurements. Reliable, local, and real time information is required to realize the full potential of precision agriculture

Site-specific irrigation: Improvement of application map and a dynamic steering of modified centre pivot irrigation system

Einleitung: Ein Management Konzept für nachhaltige und effiziente Nutzunglandwirtschaftlicher Maßnahmen ist bekannt als teilflächenspezifische Landwirtschaft (PA – Precision Agriculture). Wird das teilflächenspezifische Konzept im Bewässerungsmanagement eingesetzt, wird es teilflächenspezifische Bewässerung genannt (PI – Precision Irrigation). Bei der teilflächenspezifische Bewässerung kann die Bewässerung zwischen den Bereichen eines Feldes auf Grund der Variabilität der Bodeneigenschaften oder dem Anbau von verschiedenen Pflanzen auf dem selben Feld variieren. Die räumliche Veränderung der nutzbaren Feldkapazität als Primärfaktor bedingt die räumliche Veränderung der Bewässerungshöhe und der Bewässerungsfrequenz. Die Bewässerungssysteme verteilen das Wasser bis heute gleichmäßig, so dass die Flächen teilweise überbewässert oder unterbewässert sind. Bezogen auf dieses Problem ist die teilflächenspezifische Beregnung geeignet, das Wasser an der richtigen Stelle zum richtigen Zeitpunkt unter Benutzung des richtigen Bewässerungssystems auszubringen. Folglich sind die Schlüsselziele dieser Arbeit: a) die Abgrenzung von Beregnungsmanagementzonen (IMZs – Irrigation Management Zones) unter Nutzung von sensorbasierten Messungen der elektrischen Leitfähigkeit (ECa – depth-weighted apparent soil electrical conductivity) des Bodens mit EM38 und VERIS 3100, b) die Entwicklung und Evaluierung einer teilflächenspezifischen mobilen Tropfbewässerung und c) Auswertung von drahtlosen  Bodenfeuchtesensoren (EnviroSCAN) und der klimatischen Wasserbilanz (AMBAVModell) zur Bestimmung der Bodenfeuchte bzw. der Bewässerungshöhe.Material und Methoden: EC25-Daten (ECa bei 25° C) wurden unter Verwendung von EM38 und VERIS 3100 Geräten bei Feldkapazität auf einem 16,6 ha großen Feldstück der FAL, Braunschweig, Deutschland, gemessen. Die ECa Daten wurden im Sekundenintervall mit zwei bis drei Metern Messabstand und in Reihenabständen von etwa vier bis sechs Metern gemessen. Zur Erstellung der EC25- und Bodenfeuchte Karten wurde die Software ArcView genutzt, nachdem die Messdaten mit Hilfe des sphärischen Kriging-Verfahren interpoliert wurden. 29 Kalibrierungspunkten wurden mit Hilfe von DGPS lokalisiert, um die beste sensorbasierte Methode zur Abgrenzung der Beregnungsmanagementzonen zu bestimmen. Bodenproben wurden in 0 - 60 cm Tiefe entnommen. Der zweite Bogen der Kreisberegnungsmaschinen wurde für die teilflächenspezifische mobile Tropfbewässerung umgerüstet. Eine kontrollierte Wassermenge konnte, durch Installierung einer Pulstechnik mit Magnetventilen (SV – Solenoid Valve), einem Computer gesteuerten Programm (PLC – Programable Logic Control) und Auswechseln der Düsen durch Siplast Tropfrohre ausgebracht werden. Ein Teil des Feldversuches wurde durch EnviroSCAN Bodenfeuchtesensoren gesteuert und der andere Teil wurde durch das AMBAV-Modell gesteuert, um die Beregnungshöhe zu bestimmen. Die hydraulische Genauigkeit der Siplast Tropfrohre wurde im Labor bei unterschiedlichen Wasserdrücken von 50, 100, 150 und 200 kPa untersucht.Ergebnisse und Diskussion: Die Untersuchung zeigt, dass EC25-Daten von verschiedenen gewerblichen Sensoren auf Grund der unterschiedlichen Gewichtung der Tiefe quantitativ unterschiedlich sind. Das höchste Bestimmtheitsmaß wurde zwischen EM38_h und EM38_v (R2 = 0,55) gefunden. In dieser Arbeit wurde ein gutes Bestimmtheitsmaß zwischen nFK und den VERIS 3100 Werten gefunden. Eine Kalibrierungsgleichung zur Abschätzung der nFK von VERIS 3100-sh zeigte eine hohe Ähnlichkeit zu den nFK Daten auf und hatte das höchste Bestimmtheitsmaß (R2 = 0,77). Die Bestimmtheitsmaße zu EM38-v- und EM38-h-Daten waren niedrig und anscheinend nicht ausreichend, um die räumliche Variabilität der nFK reflektieren zu können. Ein Grund kann die größere Messtiefe von EM38 sein. Sechs Beregnungsmanagementzonen (IMZ1: 99 bis 105, IMZ2: 105 bis 116, IMZ3: 116 bis 127, IMZ4: 127 bis 138, IMZ5: 138 bis 149 und IMZ6: 149 bis 152 mm/60 cm) wurden als optimale Anzahl an Beregnungsmanagementzonen auf dem Versuchsfeld, basierend auf den fuzzy-k-Mittelwerten (Boydell and McBratney, 1999) der zufälligen Einteilung, erkannt. Es wurde gefolgert, dass unter konventioneller Beregnung IMZ1 und IMZ2 überbewässert und IMZ4, IMZ5 und IMZ6 unterbewässert wurden. Das entwickelte Konzept der Pulsbewässerung hat sich als eine zuverlässige Technik bewährt. Die Wasserapplikationsmenge war direkt proportional zur Öffnungsdauer des Ventils, und das System war in der Lage, die Wassermenge entsprechend des Bewässerungspulses zu variieren. Weiterhin war es in der Lage, 15 Reihen mit jeweils 15 Düsen zu steuern. Es gab keine offenkundigen Probleme mit dem gepulsten Wasserabgabesystem in den durchgeführten Feldversuchen. Die Kreisberegnungsmaschinengeschwindigkeit und Pulstechnik zur Bereitstellung verschiedener Wassermengen hatten einen geringen nachteiligen Einfluss auf die Gleichmäßigkeit der Beregnungshöhe. Die Gleichmäßigkeitskoeffizienten wurden durch sinkende Pulszeiten und steigende Kreisberegnungsmaschinengeschwindigkeiten gesenkt. Die Kontrolleinheit war wie erwartet in der Lage die Bodenfeuchtedaten mittels Fernmesstechnik von dem EnviroSCAN Sensor zum zentralen Modem zu senden. Obwohl der EnviroSCANBodenfeuchtigkeitssensor empfindlich und kompliziert zu benutzen und zu kalibrieren ist, wurden die Bodenfeuchtigkeitsdaten fast störungsfrei von der Kontrolleinheit empfangen, gespeichert und zum Mobiltelefon gesendet. Für die Übertragung auf den PC wurde die Software „Kurznachricht Pro 2.2“ genutzt. Anschließend wurde die differenzierte Bewässerungshöhe kalkuliert. Die Ergebnisse zeigen, dass die EnviroSCAN-Sensoren in der Lage sind, den Verlauf der Bodenfeuchte während der Wachstumsperiode erfolgreich zu verfolgen. Weniger gut arbeitet der Sensor, um die Feuchtigkeitsverhältnisse auf sandigen Böden (unter 40 cm Tiefe), trotz bodenspezifischer Kalibrierung zu bestimmen. Während dessen hat sich das AMBAV-Modell als eine Alternative zum kostenintensiven EnviroSCAN erwiesen, das in der Lage ist, die Bodenfeuchtigkeit in der Wurzelzone der Graspflanzen als eine preiswerte und verlässliche Methode zu simulieren. Das Tropfbewässerungssystem sollte auf verlässlichen Testergebnissen und nicht auf Herstellerangaben beruhen. Die Laborexperimente zeigten, dass der Einfluß des Betriebsdrucks auf den Durchfluss am Siplast Tropfer hoch signifikant war und der Tropferdurchfluß stark vom Betriebsdruck abhing. Die CV-Werte wurden auf dem ISO-Standard basierend als gut eingestuft. Aus den Laborexperimenten wurde herausgefunden, dass der in-line Siplast Tropfer eine hohe Ausbringungsgleichmäßigkeit und einen geringen Variationskoeffizienten aufweist. Das Rohrmaterial des Siplast Tropfer ist hart und unflexibel. Es sollte nach weiteren Produkten gesucht werden, die flexibler sind und somit die Kulturen schonen. Die ökonomische Analyse dieser Arbeit zeigt, dass der Kapitalbedarf pro Hektar unter teilflächenspezifische mobile Tropfbewässerung um etwa 338 € und 250 € höher liegt als bei entsprechender Tropfbewässerung in Deutschland und im Iran. Die jährlichen Fixkosten sind geringer, als bei der Tropfbewässerung (111 und 128 [€/(ha x Jahr)] in Deutschland oder im Iran). Obwohl die teilflächenspezifische mobile Tropfbewässerung teurer ist als die Beregnung mit Kreisberegnungsmaschinen, verursacht sie weniger Wasser- und Energiekosten als die Kreisberegnungsmaschinen und hat das Potenzial den Ertrag qualitativ und quantitativ, sowie den landwirtschaftlichen Gewinn zu steigern. Die Ergebnisse zeigen, als wichtige Folge des Verfahrens, dass die teilflächenspezifische mobile Tropfbewässerung nicht notwendiger Weise eine wassersparende Technologie ist, aber es kann den Wasserbedarf optimieren. Der Energiebedarf kann um 70 % und der Wasserbedarf kann um 25 % durch die teilflächenspezifische mobile Tropfbewässerung gegenüber der Kreisberegnungsmaschine gesenkt werden. Die Modellbetrachtungen zeigten, dass durch die teilflächenspezifische mobile Tropfbewässerung im Vergleich mit der konventionellen Kreisberegnungsmaschine bei Salat, Zuckerrübe,  Kartoffel und Erdbeere etwa 575, 378, 462 und 588 kWh Energie pro Hektar gespart werden können.Schlussfolgerung: Die sensorbasierte Messung der elektrischen Leitfähigkeit bei Feldkapazität von nicht salzigen Böden ist eine preiswerte, schnelle und das Bodengefüge nicht zerstörende Alternative, um die Beregnungsmanagementzone räumlich abzugrenzen und ist den Methoden der Bodenprobenahme und Luftbildauswertung vorzuziehen. Feldstudien mit größeren Bewässerungssystemen und Felder mit verschiedenen Bodentypen, Topographie oder Pflanzenbeständen sind weiterhin zu untersuchen, um die Genauigkeit des Bewässerungskonzeptes zu validieren. Vor dem Hintergrund, dass teilflächenspezifische Bewässerung in den Anfängen steckt und eine weitere Verbreitung dieser Technologie zu erwarten ist, könnten die zusätzlichen Kosten für industrielle Ausrüstungsteile gesenkt werden. Beträchtliche Forschung und Entwicklung ist noch nötig, um die möglichen Vorteile der teilflächenspezifischen Beregnung und der Flüssigdüngung besser zu realisieren, um ein positives ökonomisches Ergebnis für den Erzeuger zu sichern.Introduction: A management concept for sustainable utilization and the efficient use of agricultural inputs is known as “Precision Agriculture” (PA). The PA concept, when applied to irrigation management is known as Precision Irrigation (PI). In PI, the need for irrigation may differ between zones of a particular field due to the spatial variation of soil properties or the cropping of different plants on the same field. Spatial variation of total available water content (TAWC) as a primary factor causes spatial variation of irrigation depth and frequency within fields. While moving irrigation systems apply water at constant rates, some areas of the field may receive too much water and others not enough. In this regard, precision irrigation (PI) is capable of applying water in the right place in the right amount at the right time using the right irrigation system. Therefore the key objectives of the present study were a) Delineation of irrigation management zones (IMZs) using sensor-based soil electrical conductivity (ECa) measurement with the aid of EM38 and VERIS 3100, b) Developing and evaluating a precision mobile drip irrigation (PMDI) and c) Evaluating wireless EnviroSCAN sensors and AMBAV-models to measure the soil moisture content.Materials and methods: EC25 data (ECa in 25° C) were collected using EM38 and VERIS 3100 at field capacity on a 16.6 ha non-saline field in the FAL, Braunschweig, Germany. ECa data were obtained in 1-s intervals corresponding to a 2 to 3 m data spacing on transects spaced approximately 4 to 6 m apart. An ArcView (ESRI) software program was used to create the EC25 and TAWC maps after the readings were interpolated using a spherical kriging model. 29 calibration points taken at a depth of 0 - 60 cm depth were located using DGPS based on the ECa spatial variability pattern and with the objective of covering the whole range of ECa values present to determine the best sensor-based method to monitor TAWC. The second span of the centre pivot irrigation machine (CP) was modified to PMDI and controlled for variable-rate water application with a pulsing technique by installing solenoid valves (SV), programmable logic control (PLC) and using a Siplast drop tube instead of sprinklers. One quarter of the study field was controlled by the EnviroSCAN soil moisture sensor and another quarter was controlled by the AMBAV-model to determine irrigation depth. In addition, the hydraulic performance of the Siplast drop tube was evaluated in the laboratory by collecting discharge rates at different pressure of 50, 100, 150 and 200 kPa.Results and discussion: This study showed that, while qualitatively similar, EC25 data obtained with different commercial sensors were quantitatively different because of different depth-weighted response functions. The highest coefficients of determination (R2) were generally found between EM38_h and EM38_v (R2 = 0.55). In this study, a better value of R2 between TAWC and the VERIS 3100 readings was found. The R2 value from VERIS 3100-sh data for TAWC estimation was maximally (0.77) and matched the TAWC data quite well, whereas R2 values to EM38-h and EM38-v data were low and apparently could not adequately reflect the spatial variability of the TAWC due to the higher influence of the EM38 on deeper layers. Six IMZs (IMZ1: 99 to 105, IMZ2: 105 to 116, IMZ3: 116 to 127, IMZ4: 127 to 138, IMZ5: 138 to 149 and IMZ6: 149 to 152 mm/60 cm) were identified based on fuzzy-k-means unsupervised classification as an optimum number of IMZs within the study field. It was concluded that under conventional uniform irrigation, IMZ1 and IMZ2 were over-irrigated, whereas IMZ4, IMZ5 and IMZ6 were under-irrigated. The developed concept of pulse irrigation was a feasible and a viable technique. Water application was directly proportional to the fraction of time the valve was opened as the system was capable of controlling fifteen banks of fifteen nozzles. There were no apparent problems with the pulsing water delivery system where the field tests were conducted. CP speed and the pulsing technique used to deliver variable amounts of irrigation had little adverse effect on system uniformity and the nozzle flow rate. Uniformity coefficients were reduced by decreasing the pulsing level and increasing CP speed. The control unit was able to monitor wireless soil moisture sensors via radio telemetry and communication from the EnviroSCAN sensors to the central ISM modem, which worked as expected. Although the EnviroSCAN soil moisture sensor was found to be delicate and intricate to use and calibrate, soil moisture data were easily sent from the control unit and received by the mobile phone and then transferred to an Excel table on a computer using easy and suitable “Kurznachricht Pro 2.2” software to calculate irrigation depth. The results suggest that EnviroSCAN sensors are able to follow the general trends successfully as soil water content measured by sampling changed during the growing season, but are not a reliable sensor to repeat moisture conditions on sandy soils (at greater depths than 40 cm ) despite its soil-specific calibration. Meanwhile, an AMBAV model as a cheap and reliable alternative instead of the expensive EnviroSCAN sensor was capable of determining and simulating soil moisture in the root zone of grass crops. Drip irrigation design should be based on reliable data sets, but not on data supplied by the manufacturer. The laboratory experiments showed that the effect of operating pressure on the discharge of Siplast emitters was highly significant and the emitter discharge was strongly influenced by the operating pressure, while some deviation from the design flow rate claimed by the manufacturer occurred. CV values were classified as good, on the basis of the ISO standard. Based on the laboratory experiments, it was found that the in-line Siplast emitter has high emission uniformity and a low coefficient of variation. In spite of high emission uniformity and a low coefficient of variation of the Siplast drop tube, it must consist of hard and inflexible material. To have a shorter drip tube installed on CP, using an in-line drop tube lateral with higher emitter discharge at low operation pressure and less emitter distance is proposed. The economic analysis of this study showed that although capital requirement per hectare under PMDI is about € 338 and € 250 more than for drip irrigation in Germany and Iran, respectively, it causes perceptibly less annual fixed cost than drip irrigation (111 and 128 [€/(ha x year)] cheaper than drip irrigation in Germany and Iran, respectively). Although PMDI causes more annual fixed expenses than CP irrigation, it has less total irrigation cost per hectare and year than CP and drip irrigation and has the potential benefit to increase yield quantity, quality and farming benefit. The results showed as an important policy implication that PMDI is not necessarily a water saving technology and it does not necessarily involve a reduction in total water use, but that it can optimize water consumption. Given a reduction of energy and water consumption of 70 % and 25 %, respectively, achieved by the PMDI as compared with the CP, results showed that about 575, 378, 462 and 588 kWh energy per hectare can be saved by PMDI in comparison with the conventional CP irrigation of lettuce, sugar beet, potato and strawberry.Conclusion: Sensor-based ECa measurement at F.C. in non-saline soil can be used as a cheap, rapid and non-destructive alternative to delineate IMZ instead of using soil sampling and aerial photography methods. Field studies using larger irrigation systems and fields with different soil types, topographic or crop characteristics are recommended to validate the precision irrigation concept and to realize and ensure a positive net economic return to the producer. With due attention to the success of PI in the early stages and developments in industrial technology in the coming years, the extra costs of industrial accessories could be minimised

A site-specific and dynamic modeling system for zoning and optimizing variable rate irrigation in cotton

Cotton irrigation has been rapidly expanding in west Tennessee during the past decade. Variable rate irrigation is expected to enhance water use efficiency and crop yield in this region due to the significant field-scale soil spatial heterogeneity. A detailed understanding of the soil available water content within the effective root zone is needed to optimally schedule irrigation. In addition, site-specific crop-yield mathematical relationships should be established to identify optimum irrigation management. This study aimed to design and evaluate a site-specific modeling system for zoning and optimizing variable rate irrigation in cotton. The specific objectives of this study were to investigate (i) the spatial variability of soil attributes at the field-scale, (ii) site-specific cotton lint yieldwater relationships across all soil types, and (iii) multiple zoning strategies for variable rate irrigation scenarios. The field (73 ha) was sampled and apparent soil electrical conductivity (ECa) was measured. Landsat 8 satellite data was acquired, processed, and transformed to compare indicators of vegetation and soil response to cotton lint yields, variable irrigation rates, and the spatial variability of soil attributes. Multiple modeling scenarios were developed and examined. Although experiments were performed during two wet years, supplemental irrigation enhanced cotton yield across all soil types in comparison with rain-fed conditions. However, length of cropping season and rainfall distribution remarkably affected cotton response to supplemental irrigation. Geostatistical analysis showed spatial variability in soil textural components and water content was significant and correlated to yield patterns. There was as high as four-fold difference between available water content between coarse-textured and fine-textured soils on the study site. A good agreement was observed (RMSE = 0.052 cm3 cm-3 [cubic centimeter per cubic centimeter] and r = 0.88) between predicted and observed water contents. ECa and space images were useful proximal data to investigate soil spatial variability. The site-specific water production functions performed well at predicting cotton lint yield with RMSE equal to 0.131 Mg ha-1 [megagram per hectare] and 0.194 Mg ha-1 in 2013 and 2014, respectively. The findings revealed that variable rate irrigation with pie shape zones could enhance cotton lint yield under supplemental irrigation in west Tennessee