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Model-based evaluation of low-cost drip-irrigation systems and management strategies using saline water
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering, Environmental Geochemistry and Ecotechnology.
2007 (English)In: Irrigation science, ISSN 0342-7188, E-ISSN 1432-1319, Vol. 25, no 4, 387-399 p.Article in journal (Refereed) Published
Abstract [en]

A drip-irrigation module was developed and included in an ecosystem model and tested on two independent datasets, spring and autumn, on field-grown tomato. Simulated soil evaporation correlated well with measurements for spring (2.62 mm d(-1) compared to 2.60 mm d(-1)). Changes in soil water content were less well portrayed by the model (spring r(2) = 0.27; autumn r(2) = 0.45). More independent data is needed for further model testing in combination with developments of the spatial representation of below-ground variables. In a fresh-water drip-irrigated system, about 30% of the incoming water was transpired, 40% was lost as non-productive evaporative flows, and the remainder left the system as surface runoff or drainage. Simulations showed that saline water irrigation (6 dS m(-1)) caused reduced transpiration, which led to higher drainage and soil evaporation, compared with fresh water. Covering the soil with plastic mulch resulted in an increase in yield and transpiration. Finally, two different drip-irrigation discharge rates (0.2 and 2.5 l h(-1)) were compared; however the simulations indicated that the discharge rate did not have any impact on the partitioning of the incoming water to the system. The model proved to be a useful tool for evaluating the importance of specific management options.

Place, publisher, year, edition, pages
2007. Vol. 25, no 4, 387-399 p.
Keyword [en]
transpiration, evaporation, sprinkler
National Category
Ecology
Identifiers
URN: urn:nbn:se:kth:diva-5134DOI: 10.1007/s00271-006-0054-8ISI: 000247785100007Scopus ID: 2-s2.0-34347396379OAI: oai:DiVA.org:kth-5134DiVA: diva2:7920
Note

QC 20101102. Updated from submitted to published 20120327. Previous title: Modelling management strategies for low-cost drip-irrigation systems using saline water

Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Irrigation with saline water using low-cost drip-irrigation systems in sub-Saharan Africa
Open this publication in new window or tab >>Irrigation with saline water using low-cost drip-irrigation systems in sub-Saharan Africa
2005 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

In the scope of future population support, agricultural productivity, in particular in sub-Saharan Africa, has to increase drastically to meet the UN’s millennium development goals of eradicating extreme poverty and hunger by 2015. Water availability in the root-zone limits crop production in large parts of the developing world. As competition for fresh water increases, water of lower quality, for example saline or polluted water, is often used for irrigation. Low-cost drip systems are suitable for saline water irrigation because they effectuate a minimisation of salt accumulation, leaf burn and peaks in salt concentration. Nonetheless, all types of saline water irrigation contain the risk for causing soil salinisation. Thus, in order to achieve long-term sustainability of these systems, appropriate management strategies are needed. The choice of management practices may be influenced by local conditions such as climate, soil and irrigation water salinity. A litera-ture review showed that there is a potential for saline water irrigation in sub-Saharan Africa in water scarce areas. Low-cost drip irrigation with saline water (6 dS m-1) was successfully used to irrigate two consecutive crops of tomato in semi-arid South Africa. An integrated ecosystems model was developed to simulate long-term yield and salt accumulation in a drip-irrigated agricultural system for a range of salinities, climates and management techniques. Crop, salt and water balance data from two field experiments conducted in Israel and South Africa, respectively, were used to parameterise and test the model. Emphasis was placed on testing the usability of the model as a tool for evaluating the importance of certain plausible management options of low-cost, drip-irrigation systems. Therefore, particular focus was directed towards correctly describing soil salinity stress on plant growth and soil evaporation from a distributed (wetted and dry) surface. In addition, the model was developed to function for different climates without having to change any other parameters or variables except for the actual climatic data. Simulations were subsequently run over a 30-year period to study long-term yield and salt accumulation in the soil profile for two sites in South Africa, demonstrating the applicability of the model. Model simulations showed that high soil salinities reduced crop growth and thus increased both drainage and soil evaporation. Further, covering the soil with a plastic sheet led to a reduction of soil evaporation and a subsequent increase in both transpiration and drainage. Rainfall was crucial for the leaching of salts from the soil, and thus in regions with low levels of rainfall, a higher leaching fraction of supplied saline irrigation water has to compensate for the lack of rain. However, a high leaching fraction also causes large amounts of salt leaching, which could potentially pollute underlying groundwater and downstream ecosystems. This risk can be mitigated using mulching, which minimises non-productive water losses, thereby lowering irrigation water needs. The choice of irrigation water salinity, frequency of irrigation and soil coverage may differ between the farmer and the regional water manager due to different preferences. Furthermore, the study highlighted how environmental variables such as water use efficiency and radiation use efficiency can be used as indicators of system performance. Whereas the latter is first and foremost a general stress indicator, water use efficiency more precisely describes specific factors such as plant size, allocation patterns and evaporative demand, which will affect the exchange of carbon dioxide and water through the stomata.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. x, 26 p.
Series
Trita-LWR. PHD, ISSN 1650-8602 ; 1020
Keyword
Ecology, Water use efficiency; Radiation use efficiency, Management techniques, Modelling, Tomato, Ekologi
National Category
Ecology
Identifiers
urn:nbn:se:kth:diva-209 (URN)91-7178-063-7 (ISBN)
Public defence
2005-05-27, D3, Lindstedtsvägen 5, KTH, 10:00
Opponent
Supervisors
Note
QC 20101102Available from: 2005-05-18 Created: 2005-05-18 Last updated: 2010-11-02Bibliographically approved

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