Effects of waste water irrigation on soil properties and soil fauna of spinach fields in a West African urban vegetable production system☆
Graphical abstract
Introduction
In many cities of Sub-Saharan Africa, urban agriculture heavily relies on the use of industrial waste water (WW) for crop irrigation. But even treated WW frequently does not meet the international standards for agricultural use developed by WHO, FAO and UNEP with potential consequences for ecosystem health and functions (Corcoran, 2010). Particularly of concern in industrial WW used for agriculture is its often high level of sodium and potassium. High concentrations of both salts may cause, due to their accumulation in the soil, strong soil alkalinity leading to a pH above 8.5 (Soil Survey Division Staff, 1993). This may be accompanied by adverse effects on soil structural properties resulting in a compaction layer with low infiltration capacity (Dastorani et al., 2008, Hussain et al., 2002, Sou et al., 2013). In conjunction with high amounts of nitrates, potassium and chloride, sodium is a major driver for salinization processes in soils. This may add to the often reported problems of West African soils that suffer from poor native soil fertility, low organic carbon, low water-holding and cation exchange capacity, surface crusting and high soil surface temperatures (Bationo and Buerkert, 2001). Gypsum, or calcium-sulfate-dihydrate (Ca[SO4]·2H2O), has been often used as an amendment in saline-sodic agricultural fields to improve their soil physical and chemical properties. As gypsum dissolves, it releases calcium ions that displace sodium on the clay colloids in alkaline soils thereby improving soil structure (Shainberg et al., 1982). Given these bio-physical constraints to plant growth the preservation of soil biological properties is likewise important to secure nutrient turnover, help to suppress soil borne diseases and pests and to maintain bioturbation (Postma-Blaauw et al., 2010, Whitford, 1996). Many studies showed the important role of ground dwelling arthropods for nutrient cycling, pedoturbation and sediment transport (Butler, 1995, Garcia and Niell, 1991, Nichols et al., 2008). Particularly ants and termites are known to affect physical and chemical soil properties. The presence of ants can alter soil pH whereby the pH of alkaline soils can be decreased and that of acid soils increased (Frouz and Jilková, 2008). It is well recognized that extreme soil properties such as strong soil alkalinity and high soil salinity influence not only plant performance but also below-ground and above-ground communities of soil biota that are interlinked. However, our understanding about the mechanisms behind the effects of aboveground-belowground feedbacks is still very limited (De Deyn and Van der Putten, 2005, Scherber et al., 2010). Most studies examined invertebrate responses on effects of increased soil pH and soil salinity within the framework of urban ecology (Dunxiao et al., 1999, McIntyre et al., 2001, Santorufo et al., 2012) whereas our knowledge about industrial waste water as driving forces for arthropod distribution within agricultural soils is scarce.
Furthermore, the West African region had received so far little attention regarding the effects of agricultural practises on soil biodiversity, although in Burkina Faso up to 90% of the population depends on agriculture as their main source of income generation.
Hence, this study aimed to analyse the effects of intensive waste water irrigation on the structure and composition of soil-dwelling arthropods found on spinach fields (Spinacia oleracea L.) in a West African urban vegetable production system, using gypsum as a soil amendment to alleviate alkalinity-induced stress with potentially positive effects on soil arthropods.
Section snippets
Study site
The study was carried out at Kossodo, a municipal district of Ouagadougou, the rapidly growing capital of Burkina Faso with currently about 1.5 million inhabitants. Ouagadougou lies in the Sudan Savannah characterized by a hot and dry climate with an average annual temperature of 28 °C and a unimodally distributed annual rainfall of 780 mm. The rainy season lasts from late May to mid-October; the study itself was performed in December 2015, the early dry season.
In 2006, at Kossodo a flat area
Results
Fresh matter of marketable spinach leaves ranged from 40 to 612 g m−2 per plot, with a mean of 276 g m−2 ± 169 g m−2 (standard deviation) and was not affected by WW irrigation, gypsum amendment, soil pH, soil EC or by the direction or degree to which soil pH and EC changed during the sampling week (Fig. 1). The usage of WW for irrigation negatively affected soil pH and soil EC, two parameters that were positively related with each other (Fig. 1). Waste water irrigation also caused higher
Discussion
Spinach plants showed a high tolerance for the measured soil pH and EC of deteriorated soils within the studied urban production system of Ouagadougou where soils received high inputs of sodium and potassium due to the irrigation with industrial waste water that caused the development of alkaline conditions (Fig. 1). However, soils' physical structure is a further determining factor for plant performance and could possibly lead to restraints on spinach growth. Nevertheless, spinach is a common
Conclusions
Due to the negative effect of salt loaded WW on soil properties, this study showed a strong, small scale effect of WW irrigation on ground dwelling insects and spiders even on high taxonomic levels. Hence, the irrigation of spinach fields with sodic WW in West African urban vegetable production systems may lead to changes in aboveground arthropod species composition with presumably negative long-term effects on beneficial predatory insects and spiders with consequences on vegetable yield and
Acknowledgements
We thank Dr. Christoph Steiner for his help and teamwork, Yacouba Ganame and Boukaré Dabilgou for their assistance in field work, Institut de l’Environnement et de Recherches Agricoles (INERA) and Ibrahim Sori at Bureau National des Sols (BUNASOLS) for laboratory analysis. This study was funded by the German Federal Ministry of Education and Research (BMBF) and the Federal Ministry for Economic Cooperation and Development (BMZ) within the framework of the UrbanFoodPlus project (//www.urbanfoodplus.org
References (40)
- et al.
Host plant quality and fecundity in herbivorous insects
Annu. Rev. Entomol.
(2002) - et al.
Water Quality for Agriculture
(1985) - et al.
Soil organic carbon management for sustainable land use in Sudano-Sahelian West Africa
Nutr. Cycl. Agroecosyst.
(2001) - et al.
The influence of salt and nitrogen on herbivore abundance: direct and indirect effects
Oecologia
(1998) - et al.
Soil zoology II: colonization, distribution, and abundance of terrestrial Heteroptera in open landscapes of former brown coal mining areas
Ecol. Eng.
(2005) Soil fauna, guilds, functional groups and ecosystem processes
Appl. Soil Ecol.
(1998)Zoogeomorphology: Animals as Geomorphic Agents
(1995)- et al.
Soil microarthropods and their relationship to higher trophic levels in the Pedregal de san angel ecological reserve, Mexico
J. Insect Sci.
(2015) Sick Water?: the Central Role of Wastewater Management in Sustainable Development: a Rapid Response Assessment
(2010)- et al.
Evaluation of the effects of industrial wastewater on soil properties and land desertification
Desert
(2008)
Linking aboveground and belowground diversity
Trends Ecol. Evol.
Relationship between soil arthropods and soil properties in a Suburb of Qianjiang city, Hubei, China
Crit. Rev. Plant Sci.
Wastewater Treatment and Use in Agriculture
Effect of soil acidity on the entomophilic nematode Steinernema kraussei Steiner
Biol. Fertil. Soils
Crop Response and Management of Salt-affected Soils. Handbook of Plant and Crop Stress
Use of soil dwelling Diptera (Insecta, Diptera) as bioindicators: a review of ecological requirements and response to disturbance
Agric. Ecosyst. Environ.
The effect of ants on soil properties and processes (Hymenoptera: Formicidae)
Myrmecol. News
Burrowing beetles of the genus Bledius (Staphylinidae) as agents of bioturbation in the emergent areas and shores of an athalassic inland lake (Fuente de Piedra, southern of Spain)
Hydrobiologia
Terrestrial invertebrates as bioindicators: an overview of available taxonomic groups
J. Insect Conserv.
Interactions between aboveground and belowground biodiversity in terrestrial ecosystems: patterns, mechanisms, and feedbacks
Bioscience
Cited by (0)
- ☆
This paper has been recommended for acceptance by Charles Wong.