Wolfram Spreer

Water Tenure in Highland Watersheds of Northern Thailand: Tragedy of the Commons or Successful Management of Complexity?

In recent years, Thailand has faced serious water problems, such as water shortages in the dry season, flooding during the rainy season and pollution with agrochemicals and industrial waste. Agriculture is the main user of available water resources and accounts for 70% of the water demand. Whereas traditionally irrigation in Thailand has been supplementary during the rainy season, water is now increasingly used for irrigation during the dry season. However, other sectors are continuously increasing their share in the withdrawal of water resources. The management of water resources is characterized by institutional and legal pluralism, responsibilities being shared among as much as eight different ministries, divided into more than 30 ministerial departments (Sethaputra et al. 2001).

Alternative Techniques for Water-Saving Irrigation and Optimised Fertigation in Fruit Production in Northern Thailand

The acreage of irrigated orchards in northern Thailand has dramatically increased since the discovery of flower induction by potassium chlorate in 1998 (see Chapter 3.1). As the availability of water is limited, alternatives for the more efficient use of water and fertilisers in fruit production are urgently needed. As longan and mango represent an important share of fruit production in the area under study, they have been the main focus of research on water-saving irrigation techniques.

Online Monitoring System on Controlled Irrigation Experiment for Export Quality Mango in Thailand

Export quality fresh mango fruit requires a careful management from production to distribution in order to meet a high standard specifically for a long supply chain. In this paper, we describe our online monitoring system to observe responses of mango trees to different levels of irrigation intensities, based on which an optimal irrigation regime can be established. The system consists of different sensors for soil moisture content, sap-flow, photographs, and so on. To fully control the amount of water irrigated, rain-out shelter was installed for every tree for the experiment. Field observation data are used to compute water consumption and water stress of target trees. Preliminary results supported the practicality of this system that can further be used for quantitative assessment and numerical simulation for optimizing a production system aiming at a long supply chain.

Influence of Water Supply on CO2 Concentration in the Rootzone of Split-Root Potted Longan Trees

Longan trees are irrigated in Thailand as fruit growth takes place during the dry season. Due to the scarcity of water resources, ways for water saving irrigation are investigated. As deficit irrigation was found to have a high water saving potential, the focus was on the investigation of plant stress responses to drought, which can be used for optimizing the deficit irrigation regime. Five split-root potted longan trees in sand culture were subjected to partial rootzone drying PRD, and during six months the CO2 concentration in the rootzone was measured by rootzone probes and compared to a well-watered control. The CO2 efflux from the rootzone was found to be well correlated to the moisture regime in the substrate. However, it was necessary to correct the measured values by the values from the control to obtain a significant correlation between CO2 concentration and soil moisture. The main observed external factor influencing CO2 was the ambient temperature. It was shown that the CO2 efflux from the soil can be used as a non-destructive method for drought stress monitoring, but continuous measurement will be necessary to externalize disturbing environmental effects.

Water Allocation and Management in Northern Thailand: The Case of Mae Sa Watershed

Physical availability of water and technical means for water storage and conveyance do not necessarily guarantee access to water for all groups of society. This is particularly true for the highland areas of northern Thailand where water is the object of competition by diverse stakeholders. While agriculture remains the main user of available water resources — the sector accounts for about 80 percent of water use — other sectors, such as tourism, water companies and other industries, are continuously increasing their share of the water used. Downstream residents are becoming increasingly aware of the deleterious effects that upstream water users can have on both water quality and quantity. Hence, intersectoral competition and conflicts between upstream and downstream water users have become a widespread phenomenon in many watersheds of northern Thailand (Charoenmuang, 1994). In recent years, highland areas have faced serious problems related to water, particularly water shortages during the dry season.

Mango and Longan Production in Northern Thailand: The Role of Water Saving Irrigation and Water Stress Monitoring

With higher fruit exports from Thailand, the importance of irrigated fruit production has increased over recent years and, as a consequence, water resources have become more and more scarce. At the same time, farmers in northern Thailand are being increasingly confronted with weather anomalies. Scheduling based on plant stress avoidance or the exploitation of stress signals can optimize water use efficiency and the profitability of irrigation under changing climatic conditions. Traditional irrigation through the use of water hoses is a common management practice in northern Thailand; however, this method is inefficient, labor intensive and relatively inflexible. The introduction of micro-irrigation systems is one important component in the development of water saving irrigation practices, with cost-benefit analyses showing that investment in a micro-sprinkler system can be beneficial. As with improved irrigation, the marketable fruit yield can be increased substantially during drought years; thus, it is worthwhile changing from traditional to modern, water efficient and flexible irrigation systems. The emphasis of irrigation research is placed on increasing water use efficiency (WUE) and deficit irrigation strategies, in particular, partial root-zone drying (PRD) were found to increase WUE substantially. Under PRD only one side of a tree row is watered, while the other is left to dry-out to a predetermined level before next being irrigated. Stress responses in general decrease water consumption and vegetative growth while yield decline is usually minor. In on-station experiments, PRD treated mango and longan trees maintained yields when compared to well-watered trees. Sophisticated deficit irrigation strategies can only be applied when robust stress monitoring methods are available, and thermal imaging is one such new, non-invasive method. In the research study outlined here, the use of this method was investigated under field conditions, with our findings showing that it has the potential to be used within future irrigation scheduling systems.

Thermofotografie zur Erfassung der Variabilität von stomatärer Leitfähigkeit an Mangobäumen

Trockenstressbedingter Stomataschluss und Anstieg der Blatttemperatur verlaufen bei den meisten Pflanzen parallel. Deshalb bietet Thermofotografie eine gute Moglichkeit, einen Uberblick uber raumliche Verteilung und zeitliche Entwicklung der Transpiration zu erhalten. Dies konnte an Mangobaumen im Gewachshaus gezeigt werden. Im Freiland unterliegt die Blatttemperatur jedoch einer Vielzahl von klimatischen Einflussen, die Variabilitat innerhalb der Baumkrone ist daher starker ausgepragt. Es mussen deswegen Modelle entwickelt werden, mit denen es ermoglicht wird, Trockenstress und Blatttemperatur unter verschiedenen Bedingungen ins Verhaltnis zu setzen.