Browsing by Subject "Irrigation"

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Aspects of incorporating biodegradable textiles to improve sports turf
(2023) Stürmer-Stephan, Bastian; Griepentrog, Hans
Due to climate change and the need to save water, water consumption must be reduced not only in agriculture but also in urban areas. There are 55,072 sports fields in Germany that have to be irrigated in summer. In order to reduce the amount of irrigation, two approaches were researched and discussed in this thesis. The first approach is to adapt new sports fields to the local weather conditions. This approach is a decision support system, based on a model. The input variables are recorded weather data from the German Weather Service for the location where the new sports field is to be built, the hydrological properties of the substrates, and the expected costs. An optimized dimensioning of the rootzone layer is calculated by an EA solver of Microsoft Excel. This thickness of the layer can be used for the construction project. This was calculated exemplary for 3 locations. The presented model needs to be further evaluated through field trials. For existing sports fields, the root zone layer can only be changed with great effort. In this case, a biodegradable nonwoven can be installed in an existing sports field with drainage layer structure. This nonwoven transport water from the deeper drainage layer into the root zone of the turf through the capillaries, so that the water is available to the turf. To achieve this function, the 150 mm wide nonwoven must be installed vertically at a depth of 170 mm +-20 mm. During installation, the ground cover must not be reduced and the roughness of the surface must not be increased. In the present work, a device is presented, that cuts the turf, opens a furrow, incorporates the nonwoven and then closes the furrow. The device is mounted on the tractor and consists of a height guide, a cutting disc, a box coulter and a pressure roller. The device was tested on three plots with a layer structure in Stuttgart. The cutting disc works properly because no clogging was observed. A measurement frame equipped with an ultrasonic sensor, a laser range finder and a feeler wheel determined the surface roughness before and after incorporating the nonwoven. The results showed a significant increase in roughness. In order to reduce the negative impact to the ground surface, it would be possible to increase the ballasting of the device. However, harmful soil compaction must be avoided. The uniform working depth of the developed device was determined with a tachymeter and showed a deviation from the nominal depth of less than 20 mm. The results show that this meets the requirements for the device. Ground cover was measured before and after installing the nonwoven. The turf damage was less than 15 % of the ground cover, which meets the playability requirements. Reconsolidation was determined by penetrologger and evaluated in profile. The soil recompaction, measured as penetration resistance, was similar to the status quo, except in the area close to the nonwoven, where the recompaction failed. The furrows of the developed device can be recompacted more effectively by using two pressure roller, attached V-shaped. But it must be verified that the two pressure rollers do not cause ridge formation, as is the case with seed drills. Overall, the performance of the device can be considered positive, but improvements are still needed to improve reconsolidation. These improvements can be verified in future investigations. At the same time, the effectiveness of the nonwoven must be evaluated in the future. Preliminary tests have shown that the capillary action is sufficient to transport water from the drainage layer to the root zone.
Bedarfsgerechte Stickstoffernährung von Hopfen (Humulus lupulus L.) durch Düngesysteme mit Fertigation
(2021) Stampfl, Johannes; Ebertseder, Thomas
In terms of quantity, nitrogen is the most important and most yield limiting plant nutrient in hops (Humulus lupulus L.), whereby excess nitrogen not taken up by the hop plant is subject to various loss processes. Despite that, little is known about the exact effects of an N supply varying in rate and timing for the hop varieties and cultivation systems currently used in the Hallertau, the worlds most important hop-growing region. In the Hallertau, the required amount of nitrogen is largely supplied by surface spreading of granulated N fertilizers, whereas in semi-arid growing regions, high proportions are applied via irrigation water (fertigation). The aim of this thesis was to examine nitrogen fertilization systems with fertigation under the conditions in the Hallertau region with regard to a nitrogen nutrition that is based on the hop plant’s needs. Therefore, four research questions with different sub-aspects have been formulated, as explained below. From 2017 to 2019 the experimental research and the acquisition of empirical data has been conducted in various field trials consisting of three trial series examining the most important hop varieties at different locations. Apart from a variation in rate and timing of N fertilization, different fertilizer application forms (surface application of granulated fertilizer and above- or below-ground fertigation) have also been examined. In addition to the determination of yield, quality and N-uptake at the time of harvest, further analysis methods such as the 15N-Tracer-Technique, chlorophyll value measurements (SPAD-Meter) or passive reflection measurements were used in individual field trials to depict the N-uptake and N-distribution in different parts of the plant. a) Which effects have different nitrogen treatments varied in rate and timing? These studies found that the hop plant absorbs more than two thirds of the total amount of nitrogen over a period of 7 to 8 weeks between early June and end of July - during formation of main biomass. Despite the fact that only a low amount of nitrogen is accumulated in the plant prior to this stage, the varieties Perle and Tradition showed that a nitrogen deficit in early growth stages until end of May already leads to a decrease of yield potential. This is due to a change in the variety-characteristic formation of lateral shoots (side arms) - the later the application of nitrogen, the greater the formation of side arms was reduced, starting from the bottom to higher plant sections. Consequently, a nitrogen fertilization solely based on the hop plant’s N uptake curve cannot be recommended, neither regarding yield formation nor nitrogen utilization. Instead, an early application of the first nitrogen treatment in April is of vital importance for early maturing varieties such as Perle and Tradition. Late maturing varieties like Herkules show a higher potential of compensation due to prolonged growth phases which enables a higher adaption of N-Fertilization to the plant’s N uptake curve. The ideal amount of nitrogen fertilization with regard to yield optimization has been determined by the growth pattern - depending on variety, weather conditions and location - and therefore by the N uptake, the supply of mineral nitrogen in the soil as well as the location-specific N mineralization potential. A reduction of the nitrogen fertilization to a level significantly below the plant’s N uptake not necessarily led to a limitation of biomass and yield formation in the same year, however, it resulted in an accelerated ripening and a negative impact on external cone quality. Furthermore, it showed that the storage of nitrogen in specific storage roots declines if N levels are significantly reduced, leading to lower vitality as well as limited plant development and yield formation in the following year. With regard to the hop plant’s perennial properties as well as the goal to achieve a demand-oriented nitrogen nutrition of the hop plant it is also necessary to supply the storage roots with enough nitrogen. With respect to valuable contents of alpha acid it has been found that high N supply levels during the stage of alpha acid synthesis (starting from early August) can result in a reduction of alpha acid concentration in the variety Herkules. This decrease can be caused by late and excessive N fertilization as well as by high mineral N contents in the soil. However, this effect has not been observed in the aroma varieties Perle and Tradition. b) Is it possible to determine the current nitrogen nutritional status through non-invasive methods? The measurement of the chlorophyll value with a SPAD-Meter on the lower leaves of the main shoot generally reflected the N content and N supply status of the hop plant. However, short-term changes in the N nutritional status could not be recorded with sufficient accuracy at this measuring point, especially not during the stage of main biomass formation, since increased proportions of the applied nitrogen were transported to higher plant sections, as was shown by the use of 15N. Regarding the determination of threshold values a classification of the plant development into before, during and after main biomass formation independent of the measuring point, is considered appropriate, since the chlorophyll value correlates with the plant’s development stage. Vegetation indices, calculated on the basis of reflectance spectra, represent not only the N content but also the actual N uptake of the crop, which is why passive reflectance measurement methods have a higher informative value with regard to the current N supply status of the plant compared to chlorophyll value measurements. Therefore, this technology could be used to achieve a site-specific optimization of rate and timing of N fertilization and thus a more demand-oriented nitrogen nutrition of the hop plant in the future. c) What are the effects of surface and subsurface drip irrigation? In the period from 2017 to 2019, additional irrigation of the aroma variety Perle on sandy soil led to a stabilization of the agronomic parameters cone yield and alpha acid content every year. In addition, irrigation also achieved an improvement of nitrogen utilization. Compared to subsurface systems, surface drip irrigation achieved a higher efficiency if the horizontal water distribution was limited by hydraulic soil properties. It was shown that this is due to the fact that the majority of the hop plant’s fine root system is located in the hill formed along the hop rows and the soil layers beneath it. d) What are the effects of a nitrogen nutrition via irrigation water? A system comparison was made between N fertilization systems with fertigation and a solely granulated N application. The use of fertigation resulted not only in an improvement of cone yield and alpha acid content, but also in an increase of the plants nitrogen uptake and a reduction of Nmin content in the soil, which is also associated with a reduction of the risk of nitrate leaching into the groundwater. Fertilization systems with fertigation achieved a higher nitrogen utilization especially at low N-fertilization rates. If two thirds of the total amount of nitrogen were applied via irrigation water, the concentration over a 6-week period proved to have a positive impact on all analyzed varieties, especially under conditions of a limited N supply, since a higher proportion of N has been applied during main biomass formation and the stage of lateral shoot growth. For an efficient N-fertilization with fertigation the application should take place between mid-June and late July while no significant amounts of nitrogen should be applied after early August. For early maturing varieties such as Perle and Tradition, there is a risk of a late N application as it is hardly possible to lay out the drip tubes before the 25th week of the year. Therefore, in early maturing varieties, a higher proportion of N should be applied in earlier growth stages while the amount of N applied via fertigation should be less than two-thirds of the total amount of N fertilizer. A substantial advantage of fertilization systems with fertigation is that nitrogen applied via the irrigation water is immediately absorbed by the plants, which allows an effective short-term intervention in the plant’s nitrogen nutrition. On the basis of a reliable recording of the current N supply status with sensors during the main growth stage, fertigation could be used to adjust the N fertilization in order to achieve a site-specific and demand-oriented nitrogen nutrition of the hop plant.
Economic analysis and policy implications of wastewater use in agriculture in the central region of Ethiopia
(2008) Weldesilassie, Alebel Bayrau; Dabbert, Stephan
The general objective of this study was to analyze the impact of wastewater use in agriculture. It mainly focused on three aspects of wastewater use for irrigation and their policy implications: impact on crop production and productivity; its impact on the health of farmers; and the value attached to its safe use for irrigation. The main objectives of the study were, therefore, 1) to define the farming system of wastewater farmers and to analyze the impact of wastewater on crop productivity; 2) to analyze the prevalence of the actual health risks to farmers and estimate the health costs associated with the use of wastewater in irrigation; and 3) to estimate the farmer?s willingness to pay for improved or safe use of wastewater for crop production. This study used mainly primary data collected from a household survey conducted on 415 wastewater and freshwater farm households operating irrigated agricultural activities within and around Addis Ababa, a central region of Ethiopia. A Cobb Douglas production function is specified to analyze the impact of wastewater on crop productivity. The production function was estimated using a Censored Least Absolute Deviation (CLAD) econometric model. To analyze the health impact of wastewater, the probability of illness was estimated based on the theory of the utility maximizing behavior of households subject to the conventional farm household production model modified by adding a health production function. The economic value of safe use of wastewater is estimated from data obtained from a contingent valuation survey administered by in-person interviews. A dichotomous choice model is used to elicit the farmers? willingness to pay. Bivariate probit and interval regression models are used to analyze the factors determining the farmers? willingness to pay for safe use of wastewater for crop production. The study shows that the livelihoods of wastewater farm households depend on the wastewater farm. Income from a wastewater farm accounts for 62% of total annual household income, ranging from 27% to 97%. About 61% of the vegetable market of Addis Ababa, the capital city of Ethiopia with more than five million people, is produced from the wastewater farms. Leafy vegetables, which are eaten raw, are mainly produced in less polluted wastewater farms and root vegetables are produced in more polluted wastewater farms. The study revealed that wastewater farm households use significantly less doses of chemical fertilizer compared to the freshwater irrigators. However, they spend three times more on seed and five times more on farm labor. Net farm return per hectare of plots irrigated with wastewater is significantly higher than for plots irrigated with freshwater. The results also indicate that the predicted median output value per hectare is significantly higher in wastewater irrigated plots compared to plots irrigated with freshwater. The CLAD estimation result shows that higher productivity of wastewater plots is explained by investments in inputs (organic fertilizer, improved seed and agricultural extension services), ownership of plots and levels of pollution of the irrigation water. The overall effect of wastewater on crop productivity is negative and insignificant (compared to freshwater). Plots irrigated with less polluted wastewater are more productive than plots irrigated with more polluted wastewater. The implication of the result is that even if wastewater is a reliable source of irrigation water and contains essential plant nutrients such as NPK, the nutrient content exceeds the recommended level of the plant requirement (e.g. nitrogen) or it contains toxic elements (e.g. nickel, zinc) above the recommended limit, and thereby reduce yield. Due to unsafe wastewater irrigation systems, wastewater use in irrigation actually poses health risks to farmers. Apart from working on wastewater farms, different risk factors prevail that can cause wastewater-related diseases in the studied areas. This study shows that major risk factors causing illness are household demographic characteristics, hygienic behavior of farm families and poor access to sanitation services. Lack of awareness on health risk of wastewater as well as working without protective clothing on the farm are also important risk factors in the study area. The distribution of these risk factors varies between the wastewater and freshwater irrigation areas. The most common incidence of illness reported by farm households are intestinal infection due to hookworm and Ascaris, diarrhea and skin diseases, which also varies between the two groups of farmers as well as within the different areas of wastewater. The findings of this study show that the prevalence of illness is not only significantly higher in farmers working on wastewater farms compared to freshwater irrigators, but is also significantly higher in wastewater areas where the pollution level is higher. The probability of being sick with an intestinal illness is 15% higher for wastewater farmers than for freshwater farmers. Use of protective clothing during farm work and awareness of health risks in working on wastewater farms significantly reduce illness prevalence. In addition, hygienic behavior of farm families including eating safe raw vegetables, compound sweeping, and washing hands before a meal are important determinants of illness prevalence in wastewater irrigation areas. Therefore, use and provision of protective clothing at affordable prices, creating awareness for safe use of wastewater, and reducing the pollution level of irrigation water can significantly decrease the health risk of wastewater use in irrigation. While each of these policy interventions has a significant effect in reducing health risks, combining these measures will result in more significant reduction of health risks to farmers, and thereby maximize the benefit from the wastewater resource as a source of livelihood and vegetable supply to the residents of nearby cities. Farmers are willing to contribute money to improve the existing unsafe irrigation system. Two options were suggested by farmers to improve the existing situation: enforcing laws against polluters who discharge their wastewater without any kind of treatment, and awareness creation of safe use of wastewater for irrigation. Farmers are willing to pay for the improvement programs and there is a welfare gain to the society from safe use of wastewater for crop production. The benefit from irrigated-farming, membership to water users? association, yield value, off-farm income and working on a wastewater farm all significantly determine the farmers? probability of accepting offered bids for the improvement program. In addition to these variables, multi-purpose uses of irrigation water as well as education level determines the farmers? willingness to pay. Irrigation method has no significant effect on the farmers? willingness to pay, implying that introducing water saving and improved irrigation techniques has an important role in improving the situation without affecting the farmers? willingness to pay. Overall, this study shows that wastewater is a means of livelihood for many poor households, but the existing use of wastewater for crop production actually causes health risks both to farmers and consumers. Farmers are willing to contribute to programs designed to improve the existing situation so that it is possible to maximize the livelihood benefit at minimum health risks. However, the results do not necessarily imply that the cost of improving the situation has to be borne by the farmers only. Although the study focuses on the central region of Ethiopia, most conclusions can have a wider application in other parts of the country and in many sub-Saharan African countries where wastewater is used for irrigation.
Genotypic responses of rice to alternate wetting and drying irrigation in the Mekong Delta
(2023) Johnson, Kristian; Vo, Thuong Ti Bach; Van Nha, Duong; Asch, Folkard
In the Vietnamese Mekong Delta (VMD), alternate wetting and drying (AWD) in rice (Oryza sativa L.) production during the dry season has the potential to reduce greenhouse gas emission and freshwater use. However, its effect on yield compared with continuously flooded systems can vary. To evaluate the effect of AWD on yield and yield‐forming processes on genotypes commonly grown in the VMD, field trials over two consecutive dry seasons were conducted at the Loc Troi Group's agricultural research station in the VMD. We observed a significant yield reduction, 7% on average, across all varieties grown under AWD. Analysis of yield components showed that under AWD, genotypes on average produced more tillers, but fewer spikelets, suffered greater spikelet sterility and had a lower 1000 grain weight. The size of this effect differed between dry seasons. Accordingly, we were able to identify and characterize genotypes better suited to AWD. We also could relate shifts in sink‐source relationships to the overlap of drying events and key phenological stages other than flowering. Our study shows how successful implementation of AWD requires adaptation to both environment and genotype.
Microeconomic analysis of policies addressing food security, water and energy trade-offs in Malawi
(2017) McNulty, Emily; Zeller, Manfred
The increasing pressure from the world’s population on limited natural resources has reached an urgent level. The global demand for water, food, and energy is unsustainable, and poses a threat to human health, political stability, and environmental well-being. The poor in developing countries are most vulnerable to the negative effects of the exploitation of constrained resources, and the segregation of development programs by sector means that policy interventions do little to help. Currently, development policies are created in isolation from one another, within their own sectoral realms, and inter-sector coordination is rare. Policy interventions that affect more than one sector are key to holistic, sustainable development, but because they face an ownership issue, not falling under any one sector’s jurisdiction, they often go unaddressed. The alternative to the status quo is the use of a nexus perspective, which emphasizes the interconnectedness of sectors and seeks to implement policy interventions with the best net outcomes. Policy makers are encouraged to adopt “systems thinking”, to resist over-focused investments and interventions, and to seek regulatory cooperation. The body of nexus literature is growing mainly with the establishment of theoretical frameworks and macroeconomic studies that model outcomes of nexus interventions. This thesis contributes to the pool of nexus literature with microeconomic studies that are evaluated from the perspective of the food-energy-water (FEW) nexus. Microeconomic analysis is valuable to the nexus perspective not only because it informs macroeconomic models, but also because it provides empirical evidence of nexus forces at work. The subjects of the three studies contained in this thesis are smallholder farmers in Dedza, Malawi. The first study investigates the farmers’ willingness to invest in communally-owned irrigation schemes and the household socioeconomic characteristics that determine that willingness. The study is intended to inform Irrigation Management Transfer (IMT) programs, to help smooth the process of the transfer of irrigation scheme ownership from the government to local stakeholders. The promotion of IMT programs is considered a FEW nexus intervention because irrigation affects not only the water sector, but also the energy and food sectors. The second study in this thesis elicits smallholder farmers’ preferences for a conditional cash transfer (CCT) over a fertilizer subsidy coupon, with the intent of presenting policy makers with an alternative to Malawi’s Farm Input Subsidy Program (FISP). The narrow focus of the FISP, combined with its astronomical budget and disputed impact, indicate that it is time for an alternative, nexus-oriented intervention. The conditionality of a CCT means it can be targeted directly at certain sectors, and because beneficiaries are free to spend the cash as they choose, the impact will be spread over all three sectors. The third study in this thesis explores smallholder farmers’ willingness to pay (WTP) for improved cookstoves (ICS) and the socioeconomic characteristics that determine their WTP, to assist ICS promoting programs with pricing and targeting. Widespread sustained ICS adoption and the resulting fuel savings would directly affect the food and energy sectors, and indirectly affect the water sector. The high morbidity rates caused by reliance on biomass fuels for cooking would decline with sustained ICS adoption and proper use, resulting in human health improvements that would affect all three nodes of the nexus. There would be further indirect effects on all three sectors resulting from advancements in gender equality and climate change mitigation. While the findings of these studies have interesting implications for the FEW nexus, the interventions in question should be applied in an economy-wide model to determine the nexus effects. Such coordination of micro- and macroeconomic research, coupled with the inter-sector perspective, characterize the nexus approach and the future of development policy.
Reducing irrigation water supply to accomplish the goal of designing sustainable cropping systems in the North China plain
(2007) Binder, Jochen; Claupein, Wilhelm
An International Research Training Group (IRTG) of the University of Hohenheim and the China Agricultural University, entitled ?Modeling Material Flows and Production Systems for Sustainable Resource Use in the North China Plain? was launched in 2004. The major hypothesis was ?that adjustments in cropping systems and management practices provided potential for sustainable resource protection on a high yield level?. The research program was conducted in one of the most important economic and agricultural regions in China, the North China Plain (NCP). The NCP is one of the major maize (Zea mays L.) and wheat (Triticum aestivum L.) growing areas. A literature review indicated that over the last two decades yields for wheat and maize increased by more than 20%, which had mainly been achieved by augmenting the amount of irrigation water and fertilizer. Besides the positive effects on yield an increasing amount of these input factors leads to many environmental problems. Field experiments were carried out to compare different cropping systems. Currently, the double cropping of winter wheat and summer maize is the common cultivation system in the NCP. It consists of growing two crops mostly winter wheat and summer maize in one year. The winter wheat production depends on a supplemental irrigation, because rainfall is concentrated in the summer months during the maize growing season. An alternative to the intensive double cropping system could be the single cultivation of spring maize. Relative less irrigation water is required for spring maize production, because the rainy season coincides with the main part of the maize growing season. Due to the longer growing season spring maize normally realises higher yields in comparison to summer maize. However, the total yield of a double copping system of wheat and maize is higher. The evaluated system three harvests in two years (winter wheat and summer maize in the first year followed by spring maize in the second year) forms a balance between the double cropping system and the single cropping of spring maize. Due to the fact that three crops are grown in two years total yield is higher in comparison to single cropping of spring maize (two harvests in two years) but lower in comparison to the traditional double cropping system (four harvests in two years). However the lower cropping index in contrast to the double cropping of wheat and maize results in a lower demand of the input factors irrigation water and N-fertilizer whereas in comparison to the single cropping of spring maize a higher amount of input factor is required. Besides the conduction of field experiments for the collection of empirical datasets, the CERES-Maize and CERES-Wheat models were used to quantify the effects of different irrigation management practices on crop growth, productivity and sustainability of agricultural production. Results indicated that there is a considerable potential for reducing the irrigation amount for winter wheat. However, the results also showed that a supplemental irrigation at critical growth stages seems to be essential to maintain high yields and to ensure an adequate gross margin. In a more complex approach the CERES-Maize model was used to simulate the yield of summer maize and spring maize across the NCP. The spatial and temporal climate variability was taken into account by using up to 30 years of weather data from 14 meteorological stations. The simulated results were linked to a Geographic Information System (GIS). Results indicated that the yield distinction between summer maize and spring maize was partially very low as a result of water shortage at flowering stage. A delay in sowing and the use of adapted cultivars with a later flowering date could help to increase spring maize yields. Summarizing, the results of this study indicate that water is one of the most limiting factors for crop production in the NCP. Further, the reduction of total water consumption will become more and more important with water becoming increasingly scarce and thus costly. Consequently agriculture has to undergo and is already undergoing dramatic changes. The results of this study indicated that there are several possibilities optimize cropping systems in the NCP, focussing on a more sustainable use of water while maintaining high yields. In this context, crop models are valuable tools for e.g. irrigation planning or evaluating different cropping designs in the NCP.
Role of irrigation water pricing in sustainable water resources management along the Tarim river, Northwest China
(2016) Mamitimin, Yusuyunjiang; Doluschitz, Reiner
The main objectives of the study are to explore whether irrigation water pricing can lead to efficient water use in agriculture along the Tarim River. To understand land and water use development and driving forces along the Aksu-Tarim Basin, a workshop was conducted in Urumqi which is capital city of Xinjiang Uyghur Autonomous Region. Local experts from different research disciplines as well as relevant stakeholder participated in the workshop. Besides, data were collected and analyzed from preselected sources such as statistical yearbook and government’s official document. Research results embedded in the first article revealed that there was a huge land expansion and increase in water use for agriculture during the period from 1989 to 2011. The results also indicate that interaction of vast population growth, positive price development, agricultural profitability increase, government’s afforestation program (Grain for Green) and insufficient control of land expansion were the main driving forces for those developments. Farmers’ behavior towards the changes of irrigation water pricing is one of the important factor determining efficiency of water pricing to elicit water conservation and demand reduction. Therefore, a total of 257 farm household interviews were conducted, of which 128 served to find out farmers’ responses towards the changes of water pricing in different parts of Tarim River in July and August 2012. The results of statistical analyses are presented in the second article. Results show that only less than half of the interviewed farm households would react to increased water prices with proper changes of their farming practices leading to a more efficient water use. Results also show that increasing water prices encourage the farmers to shift their irrigation from surface water to groundwater which may result in further environmental problems. In the second article it is not possible to access the impact of different water price levels and changes in the water pricing practices because of its technicality and complexity. Besides, an irrigation water pricing reform needs to consider institutional aspects which are usually ignored in research on water pricing. Therefore, an innovative approach, Bayesian network modeling, was employed to find out the effects of different water price levels, changes in water pricing practices, and other agricultural policy options on the water use efficiency along the Tarim River. Results presented in the third article show no significant impact of water prices increased by 0-50% on water use efficiency. Solely an increase of 100% may have a relevant positive effect on water use efficiency. The model results also reveal that water pricing may provide a promising option to increase water use efficiency provided that volumetrically measuring systems, subsidies for water saving technologies, and technical support are available. The fourth article discusses the economics of cotton production and land use changes along the Tarim River from 1989 to 2009 using data from official statistical yearbooks. The results of a trend analysis indicate that the land area of cotton increased. In contrast, the area of other crops slightly decreased. Results of comparative advantage index of cotton production show that most farmers in the upper stream are more efficient in cotton production compared to farmers of the lower stream, whereas farmers in Xinjiang Production and Construction Corps are more efficient than farmers outside the Xinjiang Production and Construction Corps. The overall results of the study indicate that irrigation water pricing is not the best option to achieve an efficient water use in agriculture along the Tarim River. It requires additional adjustments and supportive agricultural policies such as the availability of volumetric measuring systems, subsidies for water-saving technologies, technological support for farmers, as well as a further institutional reform. Besides, special attention should be given to the protection of groundwater resources, especially when water prices increase. Furthermore, additional research is needed to examine the impacts of water pricing on farmers’ welfare, and the role of transferable water rights and water user associations in terms of an efficient water use along the Tarim River.
The impact of irrigated biomass plantations on mesoscale climate in coastal arid regions
(2015) Branch, Oliver; Wulfmeyer, Volker
Large-scale agroforestry in coastal arid and semi-arid regions could provide a geoengineering solution to anthropogenic climate change. Since agroforestry may impact on mesoscale climate in unknown ways, urgent research into potential impacts of large-plantations is needed to fully assess the viability and optimal placement for such schemes. Validated mesoscale simulations provide insights into feedbacks between land surface and atmosphere, particularly with respect to convective processes. Simulations of irrigated Simmondsia chinensis (jojoba) plantations were carried out with the WRF-NOAH atmosphere-land surface model using prescribed land surface and plant parameters. A sub-surface irrigation algorithm was developed based on critical soil moisture stress levels and implemented into the model code. The simulation of desert and plantation land surfaces was validated with field data from two sites in the Negev Desert - an arid desert site and a 400 ha jojoba plantation. For desert and vegetated surfaces, the model output of diurnal meteorological quantities and energy fluxes generally match well with the respective observations. Diurnal 2m-temperatures over the desert and plantation are matched by the model to within ± 0.2 °C and ± 1.5 °C, respectively. Wind speeds for both surfaces match to within 0.5 ms−1 and plantation latent heat is reproduced to within ± 20 Wm−2. Subsequent to validation, larger plantations of 100 km × 100 km were then simulated in two coastal arid regions, Israel and Oman over a period of one month and compared with control runs, without plantations. In Oman, convection and precipitation were triggered or enhanced by the plantation over multiple days whereas in Israel almost no impacts were observed. Two mechanisms were responsible for observed convection initiation: turbulent vertical transport of scalars due to increased surface heating and roughness as well as a low pressure-induced convergence at the canopy leeside. The main contributors to the surface heating effect were reduced albedo and the high water-use efficiency exhibited by specialist desert species. The combination of increased net surface radiation and high stomatal resistances significantly limited transpiration and led to a surplus in sensible heat flux compared with the surrounding soils (> 100 Wm−2). In Oman, convection initiation triggered by the plantation tended to occur on days when a high mid-tropospheric temperature lapse rate and significant surface air humidity were present. Israel exhibits more stable lapse rates during summer and drier conditions aloft, both of which suppressed convection significantly, even with a similar land surface perturbation. The initiation of moist convection at the mesoscale is therefore strongly controlled by prevailing synoptic conditions. A regional climatological analysis of temperature and humidity ECMWF reanalysis data and station precipitation data indicate that the south-west of North America has particularly suitable conditions for impacts. Coastal locations in Baja California and the Sonoran Desert exhibit a seasonal concurrence of monsoonal instability, high surface humidity and integrated column water vapor, but at the same time low precipitation. Therefore plantation impacts on convection there are likely and could be beneficial in terms of higher amounts of precipitation. These findings indicate that mesoscale convective events can be triggered by large plantations within arid and semi-arid regions and that these effects may be controllable via judicious placement of such schemes. Thus arid agroforestry has the potential not only to increase precipitation and reverse desertification within arid and semi-arid regions, but also to mitigate climate change if implemented on very large scales.