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Biomass residues improve soil chemical and biological properties reestablishing native species in an exposed subsoil in Brazilian Cerrado [1]
['Thaís Soto Boni', 'Department Of Plant Protection', 'Rural Engineering', 'Soils', 'School Of Engineering', 'São Paulo State University', 'Unesp', 'Ilha Solteira', 'São Paulo', 'School Of Earth']
Date: 2022-07
Revegetation of exposed sub-soil, while a desirable strategy in the recovery processes, often fails due to extreme soil chemical properties, such as low organic matter and pH levels inhospitable to biological activities such as nutrients cycling and plant establishment. This is the case for approximately 800 ha of the Cerrado biome in Brazil, where erecting the embankment of a hydroelectric dam in the 1960’s stripped vegetation, soil, and subsoil layers thereby distorting the soil properties. This work evaluates the effectiveness of restoration management (RM) treatments, to restore the soil quality, including biological activity and chemical attributes. In a factorial scheme, RM treatments include the addition of organic residue from aquatic macrophytes (AM) at 3 rates (0, 16 and 32 t ha -1 ), combined with ash from sugar cane bagasse of agroindustrial origin (BA) at 4 rates (0, 15, 30 and 45 t ha -1 ). RM samples contrasted samples collected from undisturbed Cerrado (CER) as well as a degraded area without intervention (DAWI). The mechanized RM plots received amendments and reforestation of 10 Cerrado native tree species. After 5 years, vegetation covered up to 60% of the surface in RM treatments receiving AM32 + BA45. AM and BA residues promoted height increases in the introduced plants. All RM treatments promoted lower levels of Al 3+ than DAWI and CER. The combination of AM32 over the rates of incorporated ash increased soil pH and K values similarly to CER. Microbial-related variables, such as microbial biomass-C was the largest in CER, followed by the RM treatments, and the lowest in DAWI. The microbial quotient was no different between CER and RM treatments. The addition of residues such as AM and BA increased the vegetation covered, improved chemical and microbiological indicators. Thus, the residues used aided the recovery process of intensely degraded soils in the Cerrado area.
Funding: This work was supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) (grant number 561842/2010-8) to KLM, and by Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) master’s scholarship to TSB. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Copyright: © 2022 Soto Boni et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Introduction
With an area of approximately two million square kilometers, the Cerrado biome forms the second largest biome in South America. Anthropic threats endangering the biome’s species richness and endemism placed Cerrado on the list of critical areas for biodiversity conservation worldwide [1]. Since the 1960s, approximately half of all Cerrado area became domesticated for agriculture, livestock as well as infrastructure for transport and energy production, promoting a severe degradation of this ecosystem [2]. These land use changes led to the loss of soil quality and its functional activities, resulting in the loss of ecosystem services, such as carbon storage, nutrient cycling, and soil formation [3].
Also in the 1960s, the construction of the Ilha Solteira Hydroelectric Power Plant (HPP-ISA) fueled civil growth in the states of São Paulo and Mato Grosso do Sul, generating significant extensions of anthropogenic areas (approximately 8,000,000 m2) [4]. Building the waterways and other structures for the HPP removed native Cerrado vegetation as well as soil extending as much as 12 m deep from the surface [5, 6]. The elimination of these materials left a geological residue that resembles mined areas of very low resilience, as they are devoid of edaphic attributes that enable spontaneous plant colonization [7].
The vegetation removal and the stripping, excavation, and transportation of the soil have different effects on soil physical, chemical, and biological properties [8]. Rebuild the soil after a degradation process is an essential factor for a successful restoration process [9]. Several techniques have been used to restore and control soil losses and water runoffs, such as revegetation, which helps in recovering organic matter, restructuring the degraded soil [10], and the use of organic soil amendments to boost plant performance and soil functions [11].
For degraded Cerrado soils, amendments featuring biomass residues (e.g., aquatic macrophytes, biochar, agro-industrial residues) efficiently enrich the soils with nutrients and organic matter [12–15]. These amendments enhance biological and physical soil conditions to allow faster recovery than unamended soils still lacking organic matter [16]. Besides, the residues selected (aquatic macrophytes and ash sugarcane bagasse) were chosen due to their abundance in the study region. Aquatic macrophytes cause problems in energy-generating in the hydroelectric power plants [17], and also the region has become a major producer of sugar cane, consequently, sugar, alcohol, and residues such as bagasse, cane straw, and bagasse ash, require an alternative for disposal [18]. Combining biomass residue amendments with the reintroduction of native vegetation, which add appropriate leaves, root biomass, and root exudates, further bolster soil functioning [19].
Abundance, diversity and biochemical attributes, and metabolic activities of microorganisms can serve as indicators of soil quality improvements [20], evidencing the success of restoration programs [21].
Other recovery indicators include the microbial quotient (qMic), which defines the stock percentage of total organic carbon in the soil, and the metabolic quotient (qCO 2 ), which shows specific respiration rates according to the CO 2 released by microbial biomass as a function of time [22], it is expected that stressed soils present higher qCO 2 values than less-stressed/natural soils [23]. The low stocks of organic compounds in degraded areas reveal corresponding low values of the microbial quotient [24]. In soils of preserved areas, that is to say, under native vegetation in the Cerrado, the values of qMic range from 0.9 to 5.5 or 9 to 55% [25].
To develop tools for reconditioning these degraded areas stripped of topsoil, this work investigates whether native tree species combined with ash residue from sugarcane bagasse and/or aquatic macrophytes reestablish microbial activity and recover soil chemical properties in a severely degraded area, from where the surface horizons and native vegetation were removed and remained without vegetation cover since the 60s. We collected samples after 5 years of intervention and compared results with soils collected from an undisturbed Cerrado site as well as a degraded area without intervention.
Our hypothesis is that the addition of organic matter and nutrients, via regional residues, associated with soil tillage, can improve edaphic conditions of severely degraded soil and favor the re-establishment of vegetation and soil microbiota.
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