By Dr. Praneet Ngamsnae
Rice cultivation is a cornerstone of agricultural economies across Asia. However, one of its most persistent environmental challenges is the management of rice straw, a major byproduct often disposed of through open field burning. This practice contributes to environmental pollution and depletes soil nutrients.
In response, microbial fermentation has emerged as a sustainable alternative to burning, with fermented rice straw showing particular promise in aquacultural applications. This approach supports integrated farming systems and provides an alternative feed source.
In freshwater aquaculture specifically, fermented rice straw offers dual benefits: it serves as a cost-effective feed option while it simultaneously enhances water quality and contributes to ecological balance within these systems. This article presents the environmental impacts of rice straw burning, outlines the history and methods of rice straw fermentation, and presents its expanding role in sustainable aquaculture.
Environmental Impacts of Rice Straw Burning
Traditional burning of rice straw releases large amounts of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), which contribute to air pollution and climate change. It also emits particulate matter (PM2.5 and PM10), which cause respiratory problems and degrade air quality (Gadde 2009). Additionally, burning destroys beneficial soil microorganisms and organic matter, thus reducing long-term soil fertility (Jain 2014).
In contrast, fermentation of rice straw (e.g. for use as animal feed or compost) reduces these environmental impacts by eliminating open burning and converting the biomass into valuable products. Anaerobic fermentation, for instance, minimizes air pollutants and enhances nutrient recycling, supporting sustainable agricultural practices (Chaudhary 2022).
Applications in Aquaculture
Rice straw fermentation is an effective technique used in aquaculture to create a nutritious food source for fish and to improve water quality. This approach is sometimes colloquially called “fish sandwich” because it creates layers of beneficial microorganisms that fish can feed on amongst the straw stalks.
In aquaculture, fermented rice straw can be integrated as a substrate for microbial protein production or used as an ingredient in formulated feeds for filter-feeding fish or crustaceans (Zhou 2004). Additionally, fermented straw can be part of biofloc technology systems which recycle waste and enhance water quality through microbial processes (Crab 2012). These practices promote circular bioeconomy models and reduce reliance on commercial feeds.
A Brief History of Fermented Rice Straw in Aquaculture
The integration of fermented rice straw into aquaculture reflects a growing awareness of its potential as a sustainable and circular resource. Historically, rice straw was considered an agricultural waste product, but its fermentation has opened new possibilities in aquafeed development. This process enhances the nutritional profile of rice straw, notably improving its digestibility and transforming it into a more efficient feed component. Fermentation also contributes to waste management within aquaculture systems by recycling agricultural byproducts into valuable inputs, thus promoting environmental sustainability and reducing the ecological footprint of fish farming (Cao 2010). Such practices align with the principles of a circular economy, where waste is repurposed to support resource efficiency.
Fermentation notably increases the protein content of rice straw, when using specific probiotics (Sarungu 2020). In addition, fermentation improves nutrient bioavailability, making the feed more digestible and palatable, which supports the growth and health performance of aquatic species (Siddik 2024).
Straw Fermentation Procedure for Fishponds
The Chiang Rai Inland Aquaculture Research and Development Center (DOF) published a recipe about rice straw fermentation for use in fishponds, which typically follows the steps below.
Step 1: Collection and Pre-treatment. Rice straw is collected post-harvest, chopped into 5-10 cm lengths to increase the surface area, and soaked in water for 12-24 hours.
Step 2: Fermentation Preparation. A mixture is prepared using 100 kg chopped rice straw, 2-3 kg molasses (as a carbon source), 1-2 kg urea (nitrogen source), 1 liter of EM or a mixture of Lactobacillus spp. and yeast, and 30-40 liters of clean water.
Step 3: Anaerobic Fermentation. The mixture is packed tightly into sealed containers or covered pits (e.g. silage bags or drums) and left to ferment for 7-14 days. The fermentation period can vary depending on temperature and humidity.
Step 4: Application in Fishponds. After fermentation, the straw can be either directly applied into fishponds at 100-200 kg/rai (1 rai = 1,600 m2) to produce natural feed via microbial and phytoplankton blooms, or used in composted form to fertilize ponds before stocking fingerlings, or mixed with aquafeed as a partial feed replacement for filter-feeding species like tilapia or common carp. This last method increases the availability of microbial biomass and enhances water quality through the recycling of nutrients (Edwards 1993; Zhou 2004).
Nutritional Benefits of Fermented Rice Straw in Aquaculture
Fermented rice straw offers several nutritional benefits for aquaculture, such as enhancing the growth and health of aquatic species. The fermentation process significantly improves the nutritional profile of rice straw, making it a valuable feed ingredient. Fermentation can elevate the protein content of rice straw from approximately 5.86% to over 13% (Begum 2013), which is crucial for fish growth and development. The digestibility of microbial protein derived from fermented rice straw can reach up to 55%, which is beneficial for fish nutrition (Han 1975). Additionally, fermented rice straw shows higher levels of essential minerals such as potassium, phosphorus, calcium, and magnesium, which are vital for fish health (Begum 2013).
In terms of feed efficiency, fish fed diets containing fermented rice straw exhibit better feed conversion ratios (FCR) and specific growth rates (SGR) compared to those fed raw straw (Zaid 2009). The fermentation process yields microbial protein that is comparable to traditional protein sources like alfalfa, enhancing the overall diet quality (Han 1975).
Successful Case Studies
Several examples from Asia demonstrate effective fermented rice straw applications in aquaculture.
In Thailand, constructing compost heaps of fermented rice straw in fishponds is an effective approach to reduce the reliance on commercial feed during fish rearing. This method supports both nursery and grow-out stages by fostering the development of various natural foods such as green water, rotifers, red worms, and beneficial bacteria that fish consume. Additionally, fish can feed on fermented straw or dried grass that have decomposed, which can decrease the need for commercial feed by 30-50%. For a 1,600 m2 pond, about 500-1,000 kilograms of rice straw or dried grass per production cycle (8-12 months) is sufficient. This practice also helps to reduce pollution caused by agricultural residue burning (DOF).
Northern Vietnam’s integrated rice-fish-livestock systems utilized fermented rice straw as cattle feed, with the nutrient-rich effluent allowed to flow into fishponds. This approach increased fish yield by 20-25% without additional feed inputs by enhancing natural pond productivity and supporting plankton growth while improving overall system sustainability through effective waste reuse (Prein 2002).
In China, fermented rice straw served as both fertilizer and substrate in carp polyculture ponds. The decomposition process boosted microbial activity and natural food availability, resulting in 15-20% better growth rates for carp species. Dissolved oxygen and ammonia levels remained within safe limits, supporting ecological practices and reducing commercial feed dependency (Zhou 2004).
These cases demonstrate how fermented rice straw can be successfully integrated across different aquaculture systems and geographical contexts.
Economic Benefits
Fermented rice straw offers significant economic benefits for fish farming through cost reduction and resource efficiency. By utilizing this agricultural waste, farmers can decrease their dependence on expensive fishmeal and imported feed components, with studies showing formulation cost reductions of INR 3.5-6.1 per kg compared to untreated alternatives (INR stands for Indian rupee; 1 Indian rupee = 0.38 Thai baht = 0.012 US dollar) (Jannathulla 2022).
The fermentation process substantially enhances nutritional value, increases protein levels by up to 97% and reduces crude fiber content (Zaid 2009). This nutritional improvement leads to better feed conversion ratios and growth rates in fish, directly improving economic returns (Surianti 2021). Fish fed with fermented rice straw demonstrated higher survival rates, better growth performance, enhanced disease resistance, and improved nutrient absorption. These benefits translate to increased yields and reduced treatment costs.
Although the benefits of fermented rice straw are significant, it is essential to consider potential challenges, such as the need for proper fermentation techniques to maximize nutrient availability and the variability in nutrient profiles caused by different fermentation conditions.
Challenges to the Effective Use of Fermented Rice Straw
Despite its potential as an aquafeed ingredient, fermented rice straw faces several implementation challenges.
Quality and safety issues arise from antinutritional factors and microbial contaminants and thus require careful fermentation management. Nutritional quality varies significantly according to fermentation techniques, microorganisms used, and straw composition, creating inconsistencies that hinder reliable commercial implementation (Siddik 2024).
Socio-economic barriers include limited farmer awareness and resources, necessitating policy support and education to improve economic viability. Nevertheless, solutions to these challenges present opportunities for innovation in aquaculture sustainability, for potential enhancement of fish growth, for reduction of environmental impacts and for promotion of circular agricultural economies (Singh 2023).
Policy Interventions in Promoting Rice Straw Use
Policy interventions will play a vital role in the promotion of rice straw utilization in sustainable aquaculture. Incentive programs, technical support, and regulatory frameworks can drive the adoption of practices that convert agricultural waste into valuable inputs. Targeted subsidies, research funding, and public-private partnerships can support the development and implementation of rice straw-based innovations. Extension services can bridge the gap between applied research and field application, thus helping producers overcome technical challenges.
These measures will help promote the conversion of rice straw into products such as fish feed, pond substrates, and water quality enhancers, thus addressing waste management while supporting circular resource use. Integrated policy approaches will also foster collaboration between the agricultural and aquacultural sectors, reducing costs and generating value-added revenue streams.
Wider adoption of rice straw use requires alignment between policy, technology, and local practices. Governments and extension services should provide training, supply starter cultures, and demonstrate practical applications. Embedding rice straw use into local circular bioeconomy strategies can create economic incentives and reduce the environmental impacts of rice farming.
Conclusion
The integration of fermented rice straw into aquaculture systems represents a promising and environmentally sound innovation within sustainable agriculture. Diverting rice straw from a harmful open-field burning practice to a closed fermentation process not only mitigates greenhouse gas emissions and air pollution but also transforms agricultural waste into a nutrient-rich resource. The application of fermented rice-straw in aquaculture, particularly in systems involving filter-feeding fish species, enhances water quality, stimulates microbial activity, and reduces reliance on commercial feed inputs.
Nutritional studies have demonstrated that fermentation improves the protein content, digestibility, and mineral composition of rice straw, resulting in better growth performance, survival rate, and efficiency for cultured fish. Economically, the use of fermented rice straw supports cost-effective aquaculture practices, improves profitability for farmers and promotes circular bioeconomy principles.
Successful case studies across Asia illustrate the adaptability of this method to various ecological and socio-economic contexts. However, to scale up adoption, challenges related to fermentation consistency, quality control, farmer education, and supportive policy frameworks must be addressed. Through strategic policy interventions, technical training, and community engagement, fermented rice straw can play a transformative role in enhancing aquaculture’s sustainability, in reducing environmental degradation, and in strengthening rural livelihoods.
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