The impact of a bio-fertilizer on the soil organic matter status and carbon sequestration—results from a field-scale study
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The application of bio-fertilizers is one of the management practices that can help to maintain or increase the content of organic matter (OM) and improve soil fertility in arable soils. While some results have been obtained in relation to the influence of bio-fertilizers on organic matter content, less in known about the fractional composition of humus.
Materials and methods
The aim of this study was to determine the effects of the bio-fertilizer UGmax on soil total organic carbon (TOC), dissolved organic carbon (DOC), and the fractional composition of organic matter (C of humic acids (CHAs), C of fulvic acids (CFAs), and C in humins) in the humus horizon of an arable field. Measurements were taken in 2005 before the application of UGmax and in 2008, 3 years after its application, which was done in 2005, 2006, and 2007. Forty soil samples were taken in 2005 (the control year without UGmax), while 20 samples were taken after UGmax treatment and 20 from the control in 2008. Samples were always collected after the plants were harvested.
Results and discussion
After the 3-year period of the experiment, the TOC content was 6.3 % higher in plots on which UGmax was applied in comparison to the control, while the DOC content was 0.19 percentage points lower after 3 years of bio-fertilizer use as compared to the initial year of the experiment. The contribution of DOC to TOC decreased significantly after the application of UGmax in comparison with the control. The content of CFAs and its contribution in the TOC pools in soil without UGmax was higher at the end of the experiment compared to the beginning, while there was an inverse relationship in the soil with the bio-fertilizer. In comparison with the control, organic matter in the soil treated with UGmax had a higher content of C of humic acids, C in humins, and higher CHAs/CFAs ratio.
We conclude that the use of a bio-fertilizer that increases the stable fractions of organic matter provides evidence of an increase in the soil OM stability. In turn, the contribution of the organic matter fractions that are more resistant to decomposition is crucial for increasing soil carbon sequestration.
KeywordsBio-fertilizer C of fulvic acids C of humic acids C in humins Total and dissolved organic C
Long-term soil and crop management such as the excessive use of inorganic fertilizers and pesticides along with reduced organic manure amendments to the soil, simplified crop rotations and monocultures, the use of heavy machinery, and inadequate practices of soil management exert a considerable influence on soil quality by worsening the physicochemical and biological properties of the soil (Melero et al. 2006; Liu et al. 2010). Consequently, changes in soil management may lead to a decrease of organic matter content followed by a diminution in the sustainability of the soil, which can be expected over the long term (Valarini et al. 2003). Increasing concern about the long-term productivity and sustainability of soil quality has emphasized the need to the develop management practices that reduce the potentially negative impact of agricultural activities in which proper OM management appears to be the most important factor (Chander et al. 1997).
The content of organic matter is an essential indicator of soil quality and fertility (Haynes 2005). Organic matter is one of three soil components that are crucial for its physicochemical properties, such as its sorptive and buffer abilities as well as its biodiversity and biological activity. Because of the positive influence of organic matter on soil functionality, it is imperative that its resources be maintained or improved (Lal 2011; Krasowicz et al. 2011).
Specific OM fractions differ in mobility. The dissolved organic matter (DOM) is the most mobile fraction of organic matter. DOM is the product of the transformation and decomposition of carbon compounds that are built into soil organic material. DOM consists of simple organic compounds that have a nonspecific humic substance character (fatty acids, organic acids, amino acids, carbohydrates) and water-soluble compounds that have a humus character. The formation and translocation of DOM in soils is a very important process of organic matter transformation because the DOM takes part in the C cycling between ecosystems even though it only accounts for about 1 % of the total organic carbon in agricultural soils (Gonet and Dębska 2006; Li et al. 2014). It should be kept in mind that the content, production, and consumption of dissolved organic matter are closely related to soil microbial activity. Microbial activity not only contributes to an increase of dissolved organic substances but also affects the chemical composition of DOM, which leads to changes in its bioavailability and interaction with other dissolved substances. The susceptibility of DOM to microbiological decomposition and its rate of decomposition depend on its chemical structure and dissolved organic carbon compounds may be both the substrates as well as the products in the processes of the microbiological transformation of organic matter that lead to the formation of complex compounds (Marschner and Kalbitz 2003; Kalbitz et al. 2003; Kiikkilä et al. 2014). The humified organic matter in soil, which is operationally separated into humic acids (CHAs), fulvic acids (CFAs), and humin (C humins), is considered to be the most microbially stable reservoir of soil organic matter. Humins are the most passive fraction of humified matter. The carbon ratio of CHAs to CFAs (CHAs/CFAs) has been used as a turnover indicator to describe the intensity of the humification process of soil OM (Yang et al. 2004). However, one should note that the properties of the organic matter of soils can be modified by, e.g., the cultivation method of the land (crop rotation, fertilization) as well as by other external factors (Orlov 1986; Gonet and Dębska 1999, 2006; Dębska 2004; Dębska et al. 2012).
The successive reduction of soil OM as a consequence of the limited application of biomass to the soil as well as gas emissions and elution (such as soil dissolved carbon) has resulted in activities that are focused on increasing soil carbon fixation—its sequestration (Smith 2004). The process of carbon sequestration is defined as the fixation of carbon by plants, followed by their decomposition and humification in soil. This concept, which was proposed mainly in connection with a decrease in the emissions of greenhouse gases into the atmosphere, is now used to describe soil processes that limit soil carbon loss (Lal 2011). In recent years, interest in the prevention of soil organic matter loss has been growing rapidly and a great deal of attention has been paid to this problem in the context of the Soil Thematic Strategy of European Union, which was presented in COM Directive 232 (2006).
The application of bio-fertilizers that contain living microorganisms is one of the management practices that can help to maintain or increase the content of organic matter and improve soil fertility in arable soils. Although bio-fertilizers have been known for many years, relatively little research has been done to document their effects (or noneffects) on crop production or to provide evidence of their potential effects on soil properties and processes, especially in outstanding peer reviewed scientific journals (Dinesh et al. 2010; Khaliq et al. 2006; Mayer et al. 2010; Piotrowska et al. 2012; Wu et al. 2005; Zhao et al. 2005). Previous research has indicated positive, rarely negative, and the lack of any significant influence of bio-fertilizers on soil physicochemical and biological properties (Kaczmarek et al. 2008; Mayer et al. 2010; Tejada et al. 2011; Piotrowska et al. 2012). While some, usually contradictory, results have been obtained in relation to the influence of bio-fertilizers on the organic matter content (e.g., Valarini et al. 2003; Nisha et al. 2007; Schenck zu Schweinsberg-Mickan and Müller 2009; Pardo et al. 2010; Jakubus et al. 2013), less is known about the fractional composition of humus (Valarini et al. 2003), which impedes any further research in this field. Some researchers have noted the influence of bio-fertilizers on the acceleration of the humification of fresh organic matter that is introduced into the soil (Valarini et al. 2003; Fatunbi and Ncube 2009; Piotrowska et al. 2012). That is why, especially when a large amount of exogenous organic matter (e.g., natural fertilizers or different bio-wastes) is introduced into the soil, the application of specially composed bio-fertilizers is very important in order to accelerate the transformation of the biomass.
An increasing number of different microbial preparations for agricultural use are available on the market and an increasing interest in their use in agricultural practice, as well as a few ambiguous results of research, have led to further investigations into the relationships between the soil environment and microbial fertilizers. Consequently, the aim of the present paper was to determine the effect of the bio-fertilizer UGmax on the fractional composition of soil organic matter and to determine the role of bio-fertilizers in soil carbon sequestration and simultaneously in increasing its resources, which is part of the strategy to counteract climate changes.
2 Material and methods
2.1 Study site and soil sampling description
Chemical and microbiological composition of the UGmax biofertilizer
Elements (total values)
Lactic acid bacteria
7.5 × 102
1.6 × 105
1.8 × 104
3 × 103
Crop rotation and fertilization used in the study
Yield (Mg ha−1)
Dose (kg ha−1)
2.2 Determination of the TOC content and the composition of the soil organic matter quality
The content of total organic carbon (TOC) was determined using a Vario Max CNS analyzer (Elementar, Germany). The sensitivity of the apparatus was 0.001 g kg−1. All analyses and measurements were done at least in triplicate, as long as the error among three replications was less than 2 %.
Dissolved organic carbon (DOC) concentrations were measured in solutions that were obtained after extraction with 0.004 M CaCl2. The extraction was done using the soil sample to extractant ratio of 1:10 over 1 h. DOC content was assayed using a TOCN Multi N/C 3100 Analityk Jena (Germany) (Gonet et al. 2002). The sensitivity of the apparatus was 0.01 g L−1. DOC was measured until the measurement error was less than 2 %, and no fewer than three replications were done.
Carbon content (%)
Bulk density (kg m−3)
Decalcification (24 h) with 0.05 M HCl (1:10 w/v), Cdeca—carbon in solutions after decalcification
Extraction (24 h) of the remaining solid with 0.5 M NaOH (1:10 w/v) with occasional mixing, followed by centrifugation; C(HAs + FAs)—sum of the carbon of humic and fulvic acids
Precipitation (24 h) of humic acids from the resulting alkaline extract with 2 M HCl to pH = 2 and centrifugation; CFAs—carbon of fulvic acids in solutions
The fractional composition was expressed in mg kg−1 of dry matter of a soil sample and as the % share of the respective fractions in the TOC pool.
2.3 Statistical calculations
The dataset was analyzed in the field in a classical way in order to investigate the general status of the soil C fractions with UGmax and without the bio-fertilizer (control) in 2005 and 2008. The statistical parameters such as mean, maximum and minimum, standard deviation (SD), and coefficient of variation (CV%) were evaluated using STATISTICA v. 9.0 software. The dataset was checked for normality using the Shapiro-Wilk test (α = 5 %). Since normality was the general observation, we chose not to transform the values before further analyses. A one-way analysis of variance (ANOVA) was performed to examine the effect of the application of UGmax (UGmax and control) on the properties that were studied within the same year. In the case of significant F tests, differences between the group means were assessed using the Tukey test (p ≤ 0.05).
The coefficient of variation (CV) gives a normalized measure of spreading about the mean. Wilding (1985) proposed a classification scheme for identifying the extent of variability for soil properties based on their CV values in which values of 0–15, 16–35, and >36 % indicate little, moderate, or high variability, respectively.
3 Results and discussion
3.1 The content of TOC in soil
3.2 The content of DOC and its contribution to TOC
3.3 Fractional composition of organic matter
Content of various fractions of soil carbon (mg kg−1)
The contribution of humus fractions in TOC content (%)
The content of CFAs and its contribution in the TOC pools in soil without UGmax was higher at the end of the experiment compared to the beginning, while the relationship was inverse in the soil with bio-fertilizer (Tables 3 and 4). The data related to the CFAs indicated a slight variability as was indicated by CV values between 7.6 and 13.1 %. After 3 years of the application of UGmax, the participation of CFAs in TOC was 4.9 percentage points lower as compared to control soil (2008) (Table 4). It should be emphasized that irrespective of the experiment plot, the content and the share of CFAs in the TOC pools was higher compared to the content and contribution of CHAs. After using UGmax over a 3-year period, the difference between the contributions of CFAs and CHAs to the TOC pool decreased (Table 4).
The content of the fraction of CHAs and its contribution to TOC in the soil with UGmax was higher as compared to the control soil (Tables 3 and 4). The significant influence of a bio-fertilizer (EMs) on CHAs was noted in the study of Valarini et al. (2003) in which treatments with fresh plant debris or animal manure with the addition of EM was compared to the same plots but without a bio-fertilizer. In our study, irrespective of the experiment plot, a decrease in the content and the share of CHAs in TOC were noted during the experiment. After 3 years of the study, the mean difference in the share of CHAs in TOC between the control and UGmax soil amounted to 0.8 percentage points, while at the beginning of the experiment, it was 1.4 percentage points.
The humins fraction is the largest part of soil organic matter. In our study the participation of C humins in TOC ranged from 56.4 to 69.0 % (Table 4). At the beginning of the experiment, the mean value and the share of C humins in TOC was higher in the control soil than in the field on which UGmax was to be applied, while an inverse relationship was noted at the end of the study (Tables 3 and 4). In light of the fact that the C humins is the fraction of organic matter that is the most resistant to decomposition, its statistically significant increase may indicate the significant role of UGmax bio-fertilizer in the processes of soil C sequestration.
According to Piotrowska et al. (2012), the incorporation of UGmax into the soil significantly increased the cellulase activity, which is the group of enzymes that take part in cellulose decomposition. On the one hand, the increase of enzymatic activity may indicate the processes of the mineralization of organic matter, while on the other hand, it may indicate the beginning of the humification process. As was stated by Orlov (1986) and Ventorino et al. (2011), one of the mechanisms of humification is the polycondensation and polymerization of compounds that have a lower molecular mass that are formed from the biochemical transformation of macromolecules (cellulose, lignin). The data from this study, e.g., the higher contribution of the fraction of CHAs in TOC in the UGmax field as compared to the control (Table 4), indicates that the bio-fertilizer UGmax plays a significant role in the activation of the transformation processes, which results in the creation of macromolecular compounds.
The application of UGmax on arable soil resulted in significant changes in the quantity and quality of soil organic matter. Organic matter in the soil treated with UGmax had a higher TOC content, a higher content and contribution of CHAs and C humin in TOC, higher CHAs/CFAs ratio and a lower content of DOC as compared to the control. The use of a bio-fertilizer that increases the formation of permanent humus compounds provides evidence of an increase in the soil organic matter stability. Consequently, the contribution of the organic matter fractions that are more resistant to decomposition is crucial for increasing soil carbon sequestration. Therefore, beneficial soil microbes should be further studied and exploited for the development of sustainable agriculture as an ecological alternative for soil fertility management. Despite the fact that some research activity has been done to document the effects (or noneffects) of many bio-fertilizers on crop production or on soil processes, little is known about the mechanisms that drive bio-fertilizers and their molecular determinants. Accordingly, further investigation should be performed to recognize and improve the survival, establishment, and performance of microorganisms when applied to soil.
The authors thank the UTP University of Science and Technology in Bydgoszcz for supporting this work. Much gratitude is due to Michele Simmons for proof reading the article.
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