The intensification and expansion of the arable landscape by modern agricultural activities is amongst the greatest current threats to agro-ecosystem biodiversity mainly for many beneficial organisms and associated ecosystem services. By the year 2050, the world human population is expected to be around nine billion, where world food production has to be increased to feed the growing population. The biggest challenge the agriculture sector is going through is conserving agro-ecosystem biodiversity while maintaining food security [1]. Several studies have proven that organic farming helps maintain higher richness and abandon biodiversity in the agriculture ecosystem [2-3]. Organic farming was introduced to mitigate adverse effects, the current aims of organic farming are maintenance of soil fertility, avoidance of pollution, use of crop rotation, animal-welfare concerns and wider environmental aspects. Organic agriculture is generally considered as a sustainable production system due to less use of off–farm inputs, higher input–output efficiency and environmental benefits [4]. In a rice ecosystem, biodiversity includes genetics, species and ecosystem diversity.

Rice (Oryza sativa) is one of the world’s most important crops. It is grown in at least 114 countries worldwide [5] and is a staple food for nearly half of the world’s population. Rice production continues to be most significant in Asia, where 90% of the crop is grown, but it has also been stable or increasing in the Americas, Africa, and Europe [6]. Rice growing environments could vary depending on the irrigation, drainage, temperature, soil type and topography. They are irrigated environments, rain-fed lowland environments, deep water environments, upland environments and tidal wetlands [7]. In agro-ecosystems, biodiversity has a positive impact on    farmland    production.   Rich   biodiversity   facilitates ecosystem services such as pollination and as predators for the pests in the farmland [8].

The intensive agricultural practices used in conventional rice production, with the excessive use of agrochemicals and fertilizers have destroyed the natural habitats over the decades. Therefore it is a current requirement to review how moving from conventional rice production to organic rice production would affect ecosystem sustainability. This review may discuss the basic techniques applied in organic rice cultivation, the environmental impact of organic rice cultivation, biodiversity in the rice ecosystems, and effect of organic rice production to the farmers and consumers, and the conclusions.

Basic Techniques for Organic Rice Cultivation

When applying the organic application to the rice cultivation system, it has to be started with the initial land preparation step until the very last step of harvesting. That should include all management practices including nutrient management, irrigation management, weed management, pest and disease management and harvest management. Organic rice cultivating farmers recycle nutrients in fallow lands by flooding, which facilitates the decaying of stubble and weeds. Moreover, they apply animal manure, organic fertilizer and organic materials derived from coral reefs to incorporate macro and micronutrients into the soil [7]. Other than that crop rotation is also practiced by organic farmers worldwide to provide the nitrogen requirement for the rice plants. Studies have proven that up to 30-50% of nitrogen requirement could be supplied by leguminous green-manure crops for high-yielding rice varieties. Besides soil fertility, the next major challenge of organic rice production is weed management. Crop rotation, land leveling, seedbed preparation and water management can be considered as some of the primary weed controlling systems in organic rice cultivation. Utilizing longer crop rotation periods facilitates disturbing the weed life cycle, reducing the number of weed seeds on the soil. If the land is precisely levelled, flooding would be more effective in controlling the weeds. In organic farming no insecticide or pesticide is used to control the insects and pests. Instead some biological and mechanical methods are adopted by the rice farmers. Cultivating resistant varieties, timely planting, and controlling weeds help to control the pest and diseases [9].  Moreover farmers also adopt to control the pests such as biological control, microbial control, and planting trap crops to attract natural predators [10]. Bio-pesticides and herbal insect repellents can also apply to control pest and diseases in an organic farming field.

Environmental impact of organic rice cultivation

In conventional rice cultivation, most farmers use an excess amount of synthetic fertilizer expecting higher yields. Yet, utilizing excessive amounts of fertilizer have little effect on increasing rice yields. Instead, poor management practices, the application of agrochemicals and synthetic fertilizer can directly affect human health, decline soil fertility, contaminate water resources and reduce biodiversity [11]. Organic farming systems target to conserve the farm eco system without disturbing agro-biodiversity, thus using the environmentally friendly inputs such as green manure, bio pesticides etc. [12]. The basic objectives of organic farming are environmental, social, and economic sustainability. Several studies show that the adoption of organic rice production has been clearly increased with the educational background of the farmers [13] and [14] the farmers’ attitudes toward organic farming systems can influence the farmers practicing organic rice farming. Studies have proven that organic farming has a positive impact on land and water utilization as they have high gross margins per hectare and per megalitre of water use. Reduction of fossil fuel inputs in organic rice farming also positively impacts environmental sustainability. Reducing energy inputs for the tillage practices and utilization of grazing animals for ground preparation may facilitate sustainability. As organic farming systems do not apply any synthetic fertilizer, the nutrient contamination of the water sources could be minimized. Hence unlikely to damage the natural vegetation, the aquatic environment and wildlife habitats. Moreover, organic rice cultivation systems carryout range of management practices to manage the weeds, pests and diseases; hence the pesticides and weedicide residues may not affect the groundwater or the soil microbiota. Practicing land forming, minimum tillage, nutrient cycling and incorporating organic matter help to improve the soil fertility, hence facilitating the soil conservation. Efforts to increase soil organic matter, absences of the residues of synthetic fertilizers and pesticides, minimum soil and environmental disturbance facilitate conservation of the natural habitats in the rice agro-ecosystem [15].

Application of Integrated Farming Systems to Organic Rice Cultivation

Diversification of rice cultivation by integrating animal species, such as fish, duck Azolla etc. is an effective strategy to increase the rice ecosystem biodiversity [8]. Rice-fish farming system increases the paddy productivity and facilitates the efficient utilization of water resources. Hence it may provide an additional income to the farmer, while the cultivation system runs with the organic manure. Incorporating organic manure serves dual purposes, as a cheap feedstuff for the fish and fertilizer for the rice. That farming method may reduce the usage of synthetic fertilizers. Introducing Azolla to the rice-fish farming system would benefit both fish and rice production. The Azolla serves as an inexpensive fish feed and simultaneously it can fix nitrogen, where the rice cultivation benefits.

In addition to that, in the rice-duck integration systems, ducks mainly help to control weeds and insects in the paddy field by consuming them. Meanwhile duck droppings act as a major nutrient source for organic rice farming. This method provides an additional income to the farmer as the farmer can get an additional income simultaneously [16].

Integration of horticultural crops, such as vegetables, leafy vegetables, legumes etc. also facilitates the optimum utilization of available resources. Fruit and plantation crop integration can also be practiced under the organic rice cultivation system. Integrating all these farming systems would provide economic, social and environmental benefits. Under the ecological benefits it may help to reduce the agrochemical usage in paddy cultivation, especially the chemical fertilizers, as the necessary nutrients are readily available under the natural systems. Well managed rice-based integrated systems act as the natural ecosystems, promoting the soil fertility and soil health. In such systems, agricultural wastes are successfully recycled and facilitate the efficient utilization of available natural resources [17]. 

Biodiversity in the rice ecosystem

In the rice ecosystem, habitat, species and genetic diversity can observe. Habitat diversity can be found in the paddy field and adjacent to the cultivated field. All the beneficial and harmful insects, weeds, microorganisms in the rice ecosystem can considered as species diversity. Diversity of the rice germplasm cultivated in the field counts as genetic diversity [18]. Usually the agro ecosystem biodiversity facilitates nutrient cycling, decomposition, pollination, biological control of pests, predation, competition, allelopathy, etc. In conventional rice cultivation, most farmers tend to cultivate newly improved rice varieties, which provide a comparatively higher yield per unit area. Most of these varieties are high fertilizer responsive, photoperiod insensitive and dwarf varieties. Farmers and plant breeders have developed these varieties by utilizing the wild rice varieties, which have resistant characteristics to biotic and abiotic stresses. Therefore the germplasm conservation is essential for future crop improvements. Apart from plant diversity, species diversity is also important in the rice ecosystem. Both insect pests and their enemies live in the ecosystem. When undisturbed, the population is balanced usually pest population maintains below the threshold level. Even though inappropriate management practices, climate changes or intensive utilization of pesticides may disturb the natural balance. Microbial community in the paddy soil plays a major role in ecosystem balancing, while facilitating nutrient recycling, decomposing and increasing soil physical and chemical properties.  In addition to that weeds play a major role in the rice ecosystem. They serve as a food source and a habitat for beneficial invertebrates such as pollinators and pest predators, hence they too are supporting natural pest control and the balance of the ecosystem [18]. Loss of biodiversity in the natural rice ecosystem is caused by several factors such as cultivating only improved rice varieties, extensive use of pesticides, excess use of synthetic fertilizers, poor management practices. These are some factors that may lead to the deterioration of the biodiversity in the rice ecosystem [19]. To improve the biodiversity in the rice ecosystem some measures can be implemented such as incorporating organic matter and bio fertilizer and practicing crop rotation which can alter the available microbial community from time to time such as phosphorus solubilizing bacteria and nitrogen fixing bacteria [20].

Effect of organic rice production on Farmers and Consumers

In organic rice cultivation less initial capital is required for the inputs as less agrochemicals and synthetic fertilizers are utilized. Unlike conventional farming, organic rice producing farmers have to spend more time on their farms as organic cultivation is more labor intensive [21]. In the initial stage of the cultivation the farmer has to focus more on weed controlling as there is a huge possibility for weed emerging and suppressing the rice plants growth. Once the rice plant starts tillering and due to the organic matter accumulation on the field, less light penetration and high water retention inhibit the emergence of the weed plants. 

The application of organic manure is also a labor intensive activity in organic rice cultivation. Studies have proven that nutrient management in organic farming requires twice more labor requirements than conventional rice cultivation. On the other hand land preparation in organic cultivation is labor intensive than conventional farming as it applies minimum tillage, zero application of agrochemicals etc. In addition to that, the application of organic farming systems to the organic rice cultivation increase the household income, ensure the farmers’ food security and facilitate the optimum utilization of the available resources.

Moreover several studies have identified constraints related to organic rice farming [22]. The lengthy organic certification process, unavailability of the proper market, high cost of organic seed and fertilizer, lack of knowledge of the farmers, lack of government supports less availability of organic inputs, have been identified as the factors that hinder the organic rice cultivation in several countries [23], [24] and [25]. 

In addition to that consumer preference to purchase organic rice is gradually increasing though they are comparatively high in price. monthly income, education level, and attitude towards the environment are some aspects consumers have considered when purchasing organic rice. Thus, health concerns seem to be the main motivation among the consumers to purchase organic rice [26] and [27]. 

This review provides an overview of organic rice production and its impact on the agro-ecological biodiversity. Hence extensive research should be carried out across the rice cultivation regions to find solutions to conserve the agro-ecological biodiversity, while promoting large scale organic rice farming. Rice fields play an important role in agricultural ecosystems. Even though the conventional agricultural strategies help to improve yield per unit area, simultaneously it reduces the agro-ecosystem biodiversity, due to the extensive use of agrochemicals, cultivation of hybrid varieties etc. Different studies have proven that adopting organic farming systems to rice cultivation is a better solution for conserving the agro-ecosystems. Conserving the surrounding environments of paddy fields, improving the cropping patterns, applying integrated farming systems, promoting public awareness on ecological conservation and promoting low input farming practices are some of the options that can be implemented to maintain ecological sustainability, while ensuring the food safety through organic rice cultivation.

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