Temperature limitations in the use of hydrogels on leptosols in a semi-arid region of Brazil
Introduction
Drylands, which include arid and semi-arid ecosystems, cover 41% of the earth's surface, play an important role in the global ecosystem, and are home to more than two billion people (Hoover et al., 2020). Arid and semi-arid environments are distinctive in terms of landforms, soil, fauna, flora, and water balance. Water scarcity and high-intensity, low-frequency rainfall are characteristic of these regions (Santos et al., 2016).
The predicted global expansion of arid and semi-arid lands will increase the population affected by water scarcity and land degradation (Feng and Fu, 2013). To feed an increasing global population, it is necessary to take advantage of drylands and use their natural resources sustainably (Thombare et al., 2018). Severe water scarcity is becoming common in many arid and semi-arid regions of the world (Mohammadinezhad and Ahmadvand, 2020), with water management being one of the biggest challenges for these regions (Abobatta, 2018).
The combination of anthropic pressure and aridity led to extreme degradation of large areas of Caatinga a native xeric shrubland of the Brazilian semi-arid region, giving rise to so-called ‘desertification hotspots’. Thus, means of preserving biodiversity and developing strategies to reclaim and restore these areas are urgent (Silva et al., 2014). Additionally, soil degradation implies a reduction or loss of its productive potential. Consequently, it is necessary to find alternatives to maintain/improve agricultural production and promote recovery of degraded areas. The use of hydrogels, to facilitate habitat restoration as well as support agricultural production in semi-arid regions is essential in order to ensure natural and agro-ecosystem functionality.
Hydrogels increase water use efficiency where irrigation water is limited (Bakass et al., 2002), and have been used in dry regions to increase the soil's capacity to absorb and retain water (Zain et al., 2018), improve crop growth (Yang et al., 2018) and restoration of degraded lands (Hüttermann et al., 2009). The positive effects of hydrogels have also been related to increased soil porosity, providing better oxygenation to plant roots (Ullah et al., 2015) and reduced soil BD (Hou et al., 2018).
Considering the characteristics of arid and semi-arid regions, it is necessary to understand how high temperatures affect the efficacy of hydrogels when applied to soil. Studies have indicated that increasing temperature compromises the functionality of agricultural hydrogels, highlighting a reduction of up to 60% of the water retention capacity in soil amended with hydrogel at temperatures up to 35 °C (Andry et al., 2009). The absorption of water by hydrogels (Acrylamide-co-Potassium Acrylates) decreased (from 37 to 97%) with increasing temperature from 20 to 65 °C (Nascimento et al., 2021).
In arid and semi-arid regions of the world, including the Brazilian semi-arid region, soil temperature values ranging from 25 to 60 °C have been recorded (Correia et al., 2012; Gao et al., 2007; Reyes et al., 2016; Wu et al., 2017; Xiao et al., 2016). Inappropriate management practices (e.g. deforestation) are commonly adopted in semi-arid regions, leaving the soil exposed to the effects of temperature, as solar radiation incident is direct to the soil surface (Scharenbroch and Bockheim, 2007; Souto et al., 2005). Thus, it is important to know the extent to which soil temperature negatively affects the functionality of hydrogels for agricultural use and habitat restoration.
This research critically evaluated the impact of thermal stress and exposure time, on the efficacy of a commercial hydrogel to improve water storage capacity, soil BD, and soil porosity. The study focused on soils and environmental conditions indicative of Brazilian semi-arid regions but the results are applicable in a global context.
Section snippets
Experimental site and soil used
The study was carried out from January to June 2018 through an experiment installed and conducted at the Soil Physics laboratory of the Federal University of Ceará, located at the Campus do Pici (Fortaleza, CE, Brazil). The soil used in the experiment was a Leptsol with a sandy loam texture, collected at the Vale do Curu Experimental Farm (Pentecoste, CE) (Latitude: 3°45′S; Longitude: 39°15′W). A bulk randomly selected composite sample of the topsoil layer (0–0.2 m) was collected from areas
Results and discussion
With the F test of analysis of variance (ANOVA), a significant interaction was found for all sources of variation: θFC, θWP, AW, BD, and porosity.
Conclusions
This research demonstrates that under extreme abiotic stress, that the hydrogel tested across all temperatures and exposure times evaluated, improves the water storage capacity, soil BD, and soil porosity. The tested hydrogel has very high potential to contribute to water management in soils in arid and semi-arid regions.
The addition of the hydrogel increased the value of θFC of the soil by up to 37%. However, and critically, the increase in the θFC of the test soil caused by the addition of
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
To the Coordination for the Improvement of Higher Education Personnel (CAPES) via Pró-Integração/23038.009848/2013-03. To National Council for Scientific and Technological Development (CNPq) (process 305907/2019-0). To the Soil Physics laboratory of the Federal University of Ceará.
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2022, European Polymer JournalCitation Excerpt :The obtained BD for the untreated soil was 0.96 g/cm3, whereas soil treated with UH-1, UH-2, UH-3 and UH-4 were found to be 0.62, 0.67, 0.74 and 0.76 g/cm3, respectively. It has been reported that the addition of hydrogel facilitates the formation of macropores in the soil for which BD of the treated soil becomes lower as compared to the untreated soil [45]. This happens because when hydrogel particles are dehydrated from their swollen state, they leave voids between the soil particles [44].