Due to its high land productivity, irrigated agriculture has an increasing role in food production. In the Alentejo region (southern Portugal) the irrigated area has grown since the completion of the Alqueva dam in 2002. Climatic change patterns foreseen for the Mediterranean region (more heat extremes, less precipitation and river flow, increasing risk of droughts and decrease in crop yields) are prone to soil salinization and sodification in irrigated areas in the region. The Roxo dam has some of the higher records of water salinity and sodicity in Portugal, which makes the Roxo irrigated area (RIA) a very interesting case study. This paper aimed at two main objectives for the RIA: (i) evaluate soil salinization and sodification, and make spatial predictions of soils susceptibility to these degradation types; (ii) monitor current salinity and sodicity of the water, and simulate the effect of empirical based scenarios of water salinity and sodicity. The RIA (8250 ha) extends ~20 km along the Roxo river (northern Aljustrel), in Cenozoic sedimentary formations. Main soils mapped are: Luvisols (~40%), Fluvisols and Regosols (~20%), Gleysols and Planosols (~20%) and Vertisols (~10%). However, there are only five soil profiles with detailed analytical data from a more recent soil survey with 83 profile descriptions in the RIA and surrounding area. Irrigation water of the Roxo dam and drainage water of the Roxo river were monitored almost monthly during Jul/2014-Nov/2015 and Jun/2016-Jan/2017, for determination of electrical conductivity (EC), sodium adsorption ratio (SAR), and other parameters. Soil salinity was not a significant problem in the RIA but a potential abundance of sodic soils was found that need future confirmation. A qualitative soil salinity index applied to the RIA suggests that soils most susceptible to salinity occur to a much smaller extent when this index is obtained from the soil profile data (approach B) than when it is based on information of the soil map (approach A). During the monitoring periods, both the water of the Roxo dam and of the Roxo river were slight to moderate saline for crop growth, with no restrictions for soil infiltration. The Roxo dam received water from the Alqueva dam for the first time between June and September 2016, and a small, though regular, decrease of the water EC (0.99 to 0.76 dS m-1) was observed during the same period. Three scenarios of irrigation water, identified by Low/High EC-SAR (L-L, H-H, L-H) were simulated with the Watsuit model. Low EC water (L-L and L-H) represent wet years and show no risk of soil salinity in the rootzone. However, the risk of waterlogging increases in sodic soils, especially with the scenario (L-H). High EC water (H-H) represents dryer years and results in severe saline conditions in the rootzone. In all three scenarios, prosodic and sodic soils are most sensible to degradation by salinization, sodification or both.
ABR, IPB, UE. 2016. QARSC – Qualidade da água da albufeira do Roxo na dinâmica dos solos e das culturas agrícolas [Internet]. Associação dos Beneficiários do Roxo, Instituto Politécnico de Beja, Universidade de Évora. Aljustrel. [cited 2017 Jan 27]. Available from: http://qarsc-abroxo.opendata.arcgis.com/?mapSize=map-normal.
Abrol IP, Yadav JSP, Massoud FI. 1988. Salt-Affected Soils and their Management. FAO Soils Bulletin 39. Rome: FAO.
APHA. 1998. Standard Methods for the Examination of Water and Wastewater, 20th edition. Washington, D.C.: American Public Health Association.
Ayers RS, Westcot DW. 1985. Water quality for agriculture. FAO Irrigation and Drainage Paper 29 Rev. 1, (Reprinted 1989, 1994). Rome: FAO.
Boehner J, Selige T. 2006. Spatial prediction of soil attributes using terrain analysis and climate regionalisation. In: Boehner J, McCloy KR, Strobl J, editors. SAGA - Analysis and Modelling Applications. Goettingen: Goettinger Geographische Abhandlungen. p. 13-28.
CEC. 2006. Thematic Strategy for Soil Protection [Internet]. Communication from the Commission to the Council, the European Parliament, the European Economic and Social Committee and the Committee of the Regions. Commission of the European Communities. COM(2006)231 Final, Brussels, 22.9.2006. [cited 2017 Feb 24]. Available from: http://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52006DC0231&from=EN.
Conrad O, Bechtel B, Bock M, Dietrich H, Fischer E, Gerlitz L, Wehberg J, Wichmann V, Böhner J. 2015. System for Automated Geoscientific Analyses (SAGA) v. 2.1.4. Geosci Model Dev. 8:1991-2007. (doi:10.5194/gmd-8-1991-2015).
DGADR. 2014. Estratégia para o Regadio Público 2014-2020. Direção Geral de Agricultura e Desenvolvimento Rural. Ministério da Agricultura e do Mar. 58 p.
EDIA. 2017. O que é o Alqueva [Internet]. Sistema Global de Rega. Empresa de Desenvolvimento e Infra-estruturas do Alqueva, S.A. [cited 2017 Feb 24]. Available from: http://sigims.edia.pt/indicadoresgeograficos/indexevo.html.
EEA. 2017. Climate change, impacts and vulnerability in Europe 2016. An indicator-based report [Internet]. European Environment Agency. EEA Report No 1/2017. [cited 2017 Feb 14]. Available from: http://www.eea.europa.eu/publications/climate-change-impacts-and-vulnerability-2016 (doi:10.2800/534806).
FAO. 2011. The state of the world’s land and water resources for food and agriculture (SOLAW) – Managing systems at risk [Internet]. Rome and Earthscan, London: Food and Agriculture Organization of the United Nations. 285 p. [cited 2017 Mar 06]. Available from: http://www.fao.org/docrep/017/i1688e/i1688e00.htm.
FAO. 2017. Voluntary Guidelines for Sustainable Soil Management [Internet]. Rome: Food and Agriculture Organization of the United Nations. 16 p. [cited 2017 Feb 14]. Available from: http://www.fao.org/3/a-bl813e.pdf.
FAO, ITPS. 2015. Status of the World's Soil Resources (SWSR) - Main Report [Internet]. Food and Agriculture Organization of the United Nations and Intergovernmental Technical Panel on Soils, Rome. [cited 2017 Feb 14]. Available from: www.fao.org/3/a-i5126e.pdf.
Fuglie K. 2008. Is a slowdown in agricultural productivity growth contributing to the rise in commodity prices? Agricultural Economics 39:431-441.
IDRHa-DS. 2003. Estudo de caracterização dos solos e esboço de aptidão das terras para o regadio à escala 1:25.000 na área a beneficiar com o Empreendimento de Fins Múltiplos de Alqueva. Lisboa: Instituto de Desenvolvimento Rural e Hidráulica – Divisão de Solos, MADRP.
IUSS Working Group WRB. 2015. World Reference Base for Soil Resources 2014, update 2015. International soil classification system for naming soils and creating legends for soil maps [Internet]. World Soil Resources Reports No. 106. Rome: FAO.
Marques CMP. 2016. Caracterização do aproveitamento hidroagrícola do Roxo [Internet]. In: Associação dos Beneficiários do Roxo, Instituto Politécnico de Beja, Universidade de Évora, editors. QARSC – Qualidade da água da albufeira do Roxo na dinâmica dos solos e das culturas agrícolas. Projecto Proder 50370. Aljustrel. p. 6-24 [cited 2017 Jan 27]. Available from: http://abroxo.infoagir.pt/qarsc/livro.pdf.
Marques CMP. 2017. Personal communication.
Moore ID, Grayson RB, Ladson AR. 1991. Digital terrain modeling: a review of hydrological, geomorphological and biological applications. Hydrological Processes 5:3-30.
Pansu M, Gautheyrou J. 2003. Handbook of Soil Analysis. Mineralogical, Organic and Inorganic Methods. Berlin, New York: Springer-Verlag. 995 p.
Pebesma EJ. 2016. Package ‘gstat’. Spatial and spatio-temporal geostatistical modelling, prediction and simulation [Internet] [cited 2017 Jan 27]. Available from: https://r-forge.r-project.org/projects/gstat/.
QGIS Development Team. 2016. QGIS Geographic Information System. Open Source Geospatial Foundation Project [cited 2017 Jan 27]. Available from: http://www.qgis.org/.
R Development Core Team. 2017. The R Project for Statistical Computing [Internet]. R Foundation. Vienna, Austria [cited 2017 Jan 25]. Available from: http://www.r-project.org.
Ramos TB, Gonçalves MC, Castanheira NL, Martins JC, Santos F, Prazeres A, Fernandes M. 2009. Effect of sodium and nitrogen on yield function of irrigated maize in southern Portugal. Agricultural Water Management 96(4):585-594. (doi:10.1016/j.agwat.2008.09.023).
Ramos TB, Šimůnek J, Gonçalves MC, Martins JC, Prazeres A, Castanheira NL, Pereira LS. 2011. Field evaluation of a multicomponent solute transport model in soils irrigated with saline waters. J of Hydrology 407(1-4):129-144. (doi:10.1016/j.jhydrol.2011.07.016).
Rhoades JD, Kandiah A, Mashali AM. 1992. The use of saline waters for crop production. FAO irrigation and drainage paper 48. Rome [cited 2018 Feb 22]. Available from: https://www.ars.usda.gov/pacific-west-area/riverside-ca/us-salinity-laboratory/docs/watsuit-model/.
Richards LA, editor. 1954. Diagnosis and Improvement of Saline and Alkali Soils. Agriculture Handbook No. 60. United States Salinity Laboratory Staff. Washington, D.C.: USDA.
Schermerhorn LJG, Stanton WI, Strauss G, Abreu F, Matze K, Zbyszewski G, Ferreira OV, Freire de Andrade R. 1984. Carta Geológica de Portugal na escala 1:50 000, Folha 42-D (Aljustrel). Serviços Geológicos de Portugal. Direcção Geral de Geologia e Minas.
SNIRH. 2017. Sistema Nacional de Informação de Recursos Hídricos [Internet]. Agência Portuguesa do Ambiente, I.P. [cited 2017 Jan 25]. Available from: http://snirh.pt/.
SROA. 1970. Carta dos Solos de Portugal. 6ª Ed. Vol. I: Classificação e caracterização morfológica dos solos. Lisboa: Serv. de Reconhecimento e de Ordenamento Agrário, Sec. de Estado da Agricultura.
SROA. 1972. Carta de Capacidade de Uso do Solo. Bases e normas adoptadas na sua elaboração. 6ª ed. Boletim de Solos nº 12. Lisboa: Serviço de Reconhecimento e de Ordenamento Agrário, Sec. Estado da Agricultura. Ministério da Economia.