Rice cultivation believed to be developed in the dry zone over many years ago and now it has been distributed in all agro-ecological regions except at very high elevation. According to water availability, three major categories are been recognized as major irrigation schemes (41%), minor irrigation schemes (25%), and rainfed rice lands (34%) (Bambaradeniya et al., 2004).
Rice ecosystems are currently impacted by numerous issues which lead to reducing returns from rice production such as unsuitable soil or topographical conditions, water scarcity, biotic and environmental stress, and inefficient agronomical practices. In order to increase rice production within the context of sustainable management practices, it is important to understand and classify soil quality for paddy fields that are vulnerable to degradation (Dengiz, 2020).
Soil quality is a determinant of soil fertility and productivity, maintain environmental quality and enhance plant, animal, and human health within its own land use and ecosystem boundaries (Sanchez et al., 2003). Biological measurements such as the presence of microorganisms and their types are significant within the numerous soil properties to determine and describe soil quality, which is usually complex both in measurement and interpretation (Smith et al., 1997). Recently, the long-term adverse effect has been seriously concerned that the continuous use of inorganic fertilizers on the deterioration of soil quality in the sense of soil structure, soil health, and environmental pollution (Banik et al., 2006).
Even if the past gains in rice production through chemical fertilizer, recent observations have manifest of stagnant or declining yields is due to continuous rice growing with high levels of nitrogen fertilizer and its impacts have raised concerns about long-term sustainability (Banik et al., 2006). Excessive use of fertilizer in paddy cultivation has resulted in soil acidification, degradation, air pollution, eutrophication, and crop yield reduction. By assembling these environmental and ecological problems, the continuous application of chemical fertilizer would threaten the sustainability of agriculture in the future. The Ministry of Agriculture of Sri Lanka, expected to reduce the chemical fertilizer with the concept of balanced use of both organic and chemical fertilizers for crop production to increase the crop yield while maintaining good soil fertility (Dhanapala, 2020).
Concern about the environment, inorganic fertilizer prices, and the use of fossil fuels indicates that chemical should not be the ultimate priority rather integrated approach should be aimed at (Banik et al., 2006).
The use of developed biofilm is one of the alternatives available to reduce agriculture-related environmental pollution. Biofilm is a combination of microorganisms adherent to each other and/or biotic or abiotic surfaces and embedded in a matrix of polymers (Khan et al., 2009). Such biofilms consist of microbial cells (algal, fungal, bacterial and/or other microbial) and secreted extracellular polymeric substances (EPS) by themselves to have structural and biochemical protection from environmental stresses such as UV radiation, extreme pH, osmotic shock, and desiccation (Khan et al., 2009).
Other than that microorganisms in biofilm mode allow many advantages rather than free-living single cells that enhance protection from the surrounding, proficiency to communicate and exchange genetic material, nutrient availability, and persistence in different metabolic states such as a functioning of an organ with different types of cells (Edwards & Kjellerup, 2013). Specially, these microbial communities present on the root system act to protect the plant from adverse environmental conditions and pathogenic infections. Thereby, the association between different microorganisms can gain various advantages to the enhancement of crop growth and enhancement of nutrient absorption from the soil (Seneviratne et al., 2017).
Even though these biofilms are occurring naturally in the soil, their density is not enough to have a significant effect on soil (Premarathna et al). Thus, the production and application of such biofilmed inoculants seem to be important for plant and soil conditions. Therefore, in vitro development and application of biofilms as biofertilizers knew as biofilm biofertilizer (BFBF) is a timely need amplification of sustainable agricultural productivity (Bandara et al., 2007).
Considering the product of Fungal-bacterial biofilms (FBBs), where bacteria are attached to a fungal surface is more effective than the rhizobial monocultures as nodule-like structures are formed by FBBs on the roots of non-legumes, which act as pseudo-nodules to fix N2 biologically (Seneviratne et al., 2017).
Especially in hydroponically grown rice, endophytic microbes are very important in increasing growth and yield of plants and tolerate the environment stress will be enabled due to dormancy breaking of their seed bank by the application of FBBs with its-specific biomolecules. Application of BFBFs reduced soil pH under low light and it has been observed that lowering of soil pH help dominates fungal endophytes which produce diverse organic acids, leading to an improved photosynthesis rate.
Thereby, with higher biochemical diversity of biomolecules in exudates and biochemical expressions comparison to fungal or bacterial monocultures, FBBs lead to reinstating the lost microbial diversity by breaking dormancy of soil microbial seed banks towards functioning and sustainability in agro-ecosystems (Seneviratne et al., 2017).
On the other hand, high levels of heavy metals in soil are reasonable to decrease soil microbial activity and crop production, and it becoming severe threatens human health and the whole ecosystem (Jiang et al., 2008). Limitations such as the low abundance of microbial communities and lack of available nutrients in the environment decrease the rate of oxidizing heavy metal contaminants available in the environment (Edwards & Kjellerup, 2013).
Biofilms can manage harsh environmental conditions such that microbial communities can interact and utilize heavy metals that exist in nature as dilute components of the geochemical cycles and lower the pH enough to facilitate bio precipitation of some heavy metals (Edwards & Kjellerup, 2013).
Effective microorganisms (EM) which naturally occurring beneficial bacteria and fungi in the soil system are involved in the remediation process more efficient than phytoremediation, ability to remove or destroy hazardous contaminants such as heavy metals. Considering the translocation of heavy metals in the soil-plant system in the presence of developed FBBs in Zea mays as test plant, thus heavy metal bioavailability in the soil was increased, FBBs application showed the maximum plant biomass concluding important role of FBBs in promoting plant growth and soil quality (Seneviratne et al., 2017).
Sustainable agriculture faces constraints due to low nutrient status and rapid mineralization of soil organic matter and thereby the cation exchange capacity (CEC) of the soils is further decreased. Under such conditions, during periods of high rainfall, the efficiency of mineral fertilizers is very low as mobile nutrients such as nitrate-nitrogen (NO3−N) or potassium (K+) are readily leached from the topsoil. Thus, there is a need for a new approach to increased yields, reduced negative impacts, and enhanced sustainability (Agegnehu et al., 2016).
The efficient use of soil, crop, and climate ought to be practiced while obtaining a reasonable yield, sustaining the soil and ecological conditions. Thereby, the work undertaken within the current study is in agreement with the ‘Sustainable Development Goals’ proposed by the United Nations. Though the application of developed microbial biofilms, particularly FBBs reinstate lost microbes by breaking dormancy of soil seed banks in degraded agro-ecosystems, it is important to understand the impact on the ecosystem with their complex interactions how it leads to effective soil remediation by simulating natural environmental processes.
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