This dissertation shows a novel strategy using soil matric potential based irrigation to improve water productivity of rice cultivation which is a case study from Sri Lanka. Study contains research component and a crop modelling component.:Introduction Fundamentals and Scientific Background Literature Review New Methods for Improving Water Productivity in Rice Cultivation Results and Discussion Conclusions and Outlook

Current research concentrates on ways to investigate and improve water productivity (WP), as agriculture is today’s predominant freshwater consumer, averaging at 70% and reaching up to 93% in some regions. A growing world population will require more food and thus more water for cultivation. Regions that are already affected by physical water scarcity and which depend on irrigation for growing crops will face even greater challenges regarding their water supply. Other problems in such regions are a variable water supply, inefficient irrigation practices, and over-pumping of available groundwater resources with other adverse effects on the ecosystem. To face those challenges, strategies are needed that use the available water resources more efficiently and allow farming in a more sustainable way. This work focused on the management of sensor-based deficit irrigation (DI) systems and improvements of WP through a combined approach of simulation-optimization and irrigation experiments. In order to improve irrigation control, a new sensor called pF-meter was employed, which extended the measurement range of the commonly used tensiometers from pF 2.9 to pF 7. The following research questions were raised: (i) Is this approach a suitable strategy to improve WP; (ii) Is the sensor for irrigation control suitable; (iii) Which crop growth models are suitable to be part of that approach; and (iv) Can the combined application with experiments prove an increase of WP? The stochastic simulation-optimization approach allowed deriving parameter values for an optimal irrigation control for sensor-based full and deficit irrigation strategies. Objective was to achieve high WP with high reliability. Parameters for irrigation control included irrigation thresholds of soil-water potentials because of the working principle behind plant transpiration where pressure gradients are transmitted from the air through the plant and into the root zone. Optimal parameter values for full and deficit irrigation strategies were tested in irrigation experiments in containers in a vegetation hall with drip irrigated maize and compared to schedule-based irrigation strategies with regard to WP and water consumption. Observation data from one of the treatments was used afterwards in a simulation study to systematically investigate the parameters for implementing effective setups of DI systems. The combination of simulation-optimization and irrigation experiments proved to be a suitable approach for investigating and improving WP, as well as for deriving optimal parameter values of different irrigation strategies. This was verified in the irrigation experiment and shown through overall high WP, equally high WP between deficit and full irrigation strategies, and achieved water savings. Irrigation thresholds beyond the measurement range of tensiometers are feasible and applicable. The pF-meter performed satisfactorily and is a promising candidate for irrigation control. Suitable crop models for being part of this approach were found and their properties formulated. Factors that define the behavior of DI systems regarding WP and water consumption were investigated and assessed. This research allowed for drawing the first conclusions about the potential range of operations of sensor-based DI systems for achieving high WP with high reliability through its systematical investigation of such systems. However, this study needs validation and is therefore limited with regard to exact values of derived thresholds.

Current research concentrates on ways to investigate and improve water productivity (WP), as agriculture is today’s predominant freshwater consumer, averaging at 70% and reaching up to 93% in some regions. A growing world population will require more food and thus more water for cultivation. Regions that are already affected by physical water scarcity and which depend on irrigation for growing crops will face even greater challenges regarding their water supply. Other problems in such regions are a variable water supply, inefficient irrigation practices, and over-pumping of available groundwater resources with other adverse effects on the ecosystem. To face those challenges, strategies are needed that use the available water resources more efficiently and allow farming in a more sustainable way. This work focused on the management of sensor-based deficit irrigation (DI) systems and improvements of WP through a combined approach of simulation-optimization and irrigation experiments. In order to improve irrigation control, a new sensor called pF-meter was employed, which extended the measurement range of the commonly used tensiometers from pF 2.9 to pF 7. The following research questions were raised: (i) Is this approach a suitable strategy to improve WP; (ii) Is the sensor for irrigation control suitable; (iii) Which crop growth models are suitable to be part of that approach; and (iv) Can the combined application with experiments prove an increase of WP? The stochastic simulation-optimization approach allowed deriving parameter values for an optimal irrigation control for sensor-based full and deficit irrigation strategies. Objective was to achieve high WP with high reliability. Parameters for irrigation control included irrigation thresholds of soil-water potentials because of the working principle behind plant transpiration where pressure gradients are transmitted from the air through the plant and into the root zone. Optimal parameter values for full and deficit irrigation strategies were tested in irrigation experiments in containers in a vegetation hall with drip irrigated maize and compared to schedule-based irrigation strategies with regard to WP and water consumption. Observation data from one of the treatments was used afterwards in a simulation study to systematically investigate the parameters for implementing effective setups of DI systems. The combination of simulation-optimization and irrigation experiments proved to be a suitable approach for investigating and improving WP, as well as for deriving optimal parameter values of different irrigation strategies. This was verified in the irrigation experiment and shown through overall high WP, equally high WP between deficit and full irrigation strategies, and achieved water savings. Irrigation thresholds beyond the measurement range of tensiometers are feasible and applicable. The pF-meter performed satisfactorily and is a promising candidate for irrigation control. Suitable crop models for being part of this approach were found and their properties formulated. Factors that define the behavior of DI systems regarding WP and water consumption were investigated and assessed. This research allowed for drawing the first conclusions about the potential range of operations of sensor-based DI systems for achieving high WP with high reliability through its systematical investigation of such systems. However, this study needs validation and is therefore limited with regard to exact values of derived thresholds.

Der hydrologische Kreislauf versorgt die Menschheit mit Wasserressourcen, die für ihr Wohlergehen unabdingbar sind. Ziel dieser Arbeit ist es, das Verständnis über klimabedingte Veränderungen des hydrologischen Kreislaufs zu verbessern, wie diese die Verfügbarkeit von Wasserressourcen in der Zukunft beeinflussen und welche Möglichkeiten bestehen, den Druck auf die verfügbaren Wasserressourcen durch Verringerung des anthropogenen Wasserverbrauchs zu reduzieren. Diese Dissertation zeigt, dass der Klimawandel eine große Bedrohung für die Wasserversorgung der zukünftigen Bevölkerung darstellt. Durch Begrenzung des Anstiegs der globalen Mitteltemperatur auf 2 K oder sogar 1,5 K über das vorindustrielle Niveau können gravierende negative Auswirkungen auf die Wasserverfügbarkeit jedoch weitgehend vermieden werden. Dennoch wären einige Regionen wie der Mittelmeerraum "eher wahrscheinlich" von schwerwiegenden hydrologischen Veränderungen betroffen, und in großen Teilen der Welt könnten negative Auswirkungen auf die Wasserverfügbarkeit aufgrund der großen Unsicherheiten in den Projektionen nicht ausgeschlossen werden. Bei der Untersuchung der Nachfrageseite liegt der Schwerpunkt auf der Wassernutzung in der Tierproduktion. Diese Dissertation schätzt den gegenwärtigen Wasserverbrauch für die Produktion von Tierfutter auf 4666 km3/yr (44 % des gesamten landwirtschaftlichen Wasserverbrauchs). Große Verbesserungen der Wasserproduktivität können bei Schweinen und Geflügel durch Verbesserungen sowohl in der Futtermittelproduktion als auch in der Tierhaltung erzielt werden. Bei Wiederkäuern liegt das größte Potenzial in der Verbesserung der Tierhaltung. Allerdings geht eine effizientere Futterverwertung bei Wiederkäuern, die durch erhöhte Beigabe von Kraftfutter erzielt wird, mit einem erhöhten Wasserbedarf für die Produktion des Futters einher. Dadurch ist die Verbesserung der Wasserproduktivität bei Wiederkäuern begrenzt. / The hydrological cycle provides humanity with water resources that are essential for its well-being. The aim of this thesis is to advance the understanding of climate-related changes in the hydrological cycle, how they will affect the availability of water resources in the future, and what opportunities exist to reduce anthropogenic water use to lower the pressure on water resources. This thesis demonstrates that climate change is a large threat to freshwater supply for future populations. Limiting the increase in global mean temperature to 2 K or even 1.5 K above pre-industrial levels can mitigate most of the severe negative impacts on water resources. However, some regions such as the Mediterranean would still ‘more likely than not’ be affected by severe hydrological change, and in large parts of the world, negative impacts on water availability could not be ruled out due to the large uncertainties in the projections. On the demand side, the focus is on water use in the livestock sector. This thesis estimates that about 4666 km3/yr (44 % of total agricultural water use) are currently used for feed production for the livestock sector. Large improvements in livestock water productivity can be achieved for pigs and poultry by improvements in feed production and livestock rearing alike. For ruminants, the largest potential lies in improving livestock management. However, improving the feed use efficiency of ruminants through increased supplementation with forage crops comes at the cost of increased water requirements to produce the feed. This limits the potential for improving livestock water productivity in ruminant production.

Die Wasserproduktivität in der Tierhaltung ist von vielen Faktoren abhängig. Die Futterproduktion hat den größten Anteil am Wasserbedarf von tierischen Produkten. Weitere Einflussfaktoren sind die Leistung, die Reproduktion und der Gesundheitsstatus der Tiere, das Management und die Haltungsbedingungen. In dieser Arbeit sollte untersucht werden, wie sich diese Faktoren auf die Wasserproduktivität von Milch und Geflügelfleisch in Nord-Ost-Deutschland auswirken. Zehn unterschiedliche Futtermittel wurden hinsichtlich ihres Wasserbedarfes untersucht. Aus diesen Futtermitteln wurden die Rationen für die Tiere erstellt. Die Milchleistung der Kühe wurde zwischen 4.000 und 12.000 kg Milch pro Kuh und Jahr in 2.000 kg Schritten variiert. Für jedes Leistungsniveau wurden zwölf verschiedene Fütterungsstrategien untersucht, welche auf der Erhöhung einzelner Bestandteile der Ration basieren. Der Wasserbedarf von Leitungswasser im Stall wurde mit 38 Wasserzählern ermittelt. Für die Wasserproduktivität des Geflügelfleisches wurden vier verschieden intensive Mastverfahren untersucht. Die Wasserproduktivität steigt mit steigender Milchleistung der Kühe. Das Maximum wird bei 10.000 kg Milch pro Kuh und Jahr und Rationen mit einem hohem Gras- bzw. Maissilageanteil erreicht. Die Kühe, die im automatischen Melksystem gemolken wurden, nahmen mehr Tränkwasser zu sich, als die Kühe im Fischgrätenmelkstand. Dies ist durch die höhere Milchleistung bedingt. Im automatischen Melksystem wurden im Mittel 28,6 Liter Reinigungswasser pro Kuh und Tag benötigt. Für die Reinigung des Fischgrätenmelkstandes wurden 33,8 Liter pro Kuh und Tag genutzt. Die untersuchten Broilermastverfahren zeigten keine Unterschiede hinsichtlich der Wasserproduktivität. Die intensivere Aufzucht und bessere Futterverwertung wurde durch eine niedrigere Wasserproduktivität des Futters kompensiert. Der Anteil des technischen Wassers macht in der Milchkuh- und Broilerhaltung nur einen kleinen Teil am Gesamtwasserbedarf aus. / Livestock production is the main user of water resources in agricultural production. Water is used in animal production for producing feed, watering the animals, and cleaning and disinfecting barns and equipment. The objective of this dissertation was to quantify the effects of management strategies, such as feeding, intensity of production and the replacement process on the water productivity of milk and poultry meat in Germany. Water productivity in milk and broiler production systems was calculated based on the methodology of Prochnow et al. (2012). Own measurements of the drinking and cleaning water demand in milk production were conducted in a dairy cow barn. The study was based on site conditions of North-East Germany with common variations in farm operations. The feed production is the main contributor to water input in dairy and poultry production. The water productivity of milk increased with an increasing milk yield. The most beneficial conditions related to water productivity in dairy farming were found to be with a milk yield of approximately 10,000 kg fat corrected milk and a grass silage and maize silage based feeding. The total technical water use in the barn makes only a minor contribution to water use. Former regression functions of the drinking water intake of the cows were reviewed and a new regression function based on the ambient temperature and the milk yield was developed. In broiler production the intensification of the fattening systems did not increase water productivity. An increase of water productivity in animal production can be achieved with various management strategies with their specific influence on the production process. The feed management should be a focus of the strategies.