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Low-cost drip irrigation of tomatoes using saline water: a suitable technology for southern Africa?
KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering.
Stockholm Environment Institute.
Department of Plant Production and Soil Science, University of Pretoria.
Department of Plant Production and Soil Science, University of Pretoria.
2007 (English)In: Agricultural Water Management, ISSN 0378-3774, E-ISSN 1873-2283, Vol. 89, no 1-2, 59-70 p.Article in journal (Refereed) Published
Abstract [en]

Using saline water for. irrigation increases water productivity by freeing up fresh water that can be allocated to domestic or other uses. Drip irrigation is widely regarded as the most promising irrigation system in combination with saline water. Simple drip irrigation kits that are affordable for smallholder farmers have successfully been implemented for irrigation of vegetable gardens in several countries in sub-Saharan Africa. The possibility of using low-cost drip irrigation with saline water to successfully irrigate a common garden crop, tomatoes, was tested in this study. Two low-cost drip irrigation systems with different emitter discharge rates (0.2 and 2.5 1 h(-2)) were used to irrigate tomatoes (Lycopersicon esculentum Mill. cv. "Daniella") with water of three different salinity levels (0, 3 and 6 dS m(-1)). In addition, plastic mulch to minimise soil evaporation was also compared to a "bare soil" or uncovered treatment. Two consecutive tomato crops (spring and autumn) were produced during two growing seasons, starting from September 2003 and ending in April 2004, at the Hatfield Experimental Farm in Pretoria, South Africa. An average yield of 75 Mg ha(-1) was recorded for all treatments and seasons, which can be compared with the average marketable yield for South Africa of approximately 31.4 Mg ha(-1). Even at the highest irrigation water salinity (6 dS m(-1)), a yield above the average marketable yield was achieved, indicating that low-cost drip irrigation works well in combination with saline water. Furthermore, the study showed that the choice of drip irrigation system with regard to discharge rate is of minor importance when irrigating with saline water. However, combining low-cost drip irrigation with plastic mulch increased the yield by on average 10 Mg ha(-1) for all treatments. For the bare soil treatments, rainfall had an important role in the leaching of salts from the soils. Finally, the study showed that specific leaf area was higher at high irrigation water salinities, which is contrary to results from other studies. To be able to generalise the promising findings from this study, there is a need to mechanistically model the impact of different climates, soils and irrigation management practices, as well as the long-term sustainability of these systems.

Place, publisher, year, edition, pages
2007. Vol. 89, no 1-2, 59-70 p.
Keyword [en]
smallholder farmers, water productivity, discharge rate, plastic mulch, specific leaf area, micro irrigation
National Category
Ecology
Identifiers
URN: urn:nbn:se:kth:diva-5132DOI: 10.1016/j.agwat.2006.12.011ISI: 000245579500006OAI: oai:DiVA.org:kth-5132DiVA: diva2:7918
Note
Uppdaterad från submitted till published: 20101101. QC 20101101Available 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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