Food production still imposes significant environmental costs, particularly in rice cultivation, which is a staple for half the world's population and a crucial livelihood for over a billion small-scale farmers. Because of the way it is farmed, rice is also the food crop with the largest adverse ecological footprint, being responsible for roughly 12% of the agricultural GHG emissions, and around 30% of total freshwater withdrawals amid growing water scarcity. Rice is therefore a valuable example of the interconnections among food insecurity, poverty, and climate change
Conservation Agriculture (CA) and the System of Rice Intensification (SRI) have a global relevance for improved crop production, poverty alleviation, food security, and climate change adaptability and mitigation. Taking advantage of the possible combination of CA and SRI approaches would allow rice farmers to intensify their cropping systems more sustainably.
CA is a system of land and farm management that optimises farming productivity and ecosystem services ultimately offering an alternative to the predominant Green Revolution paradigm. CA is based on three basic, interlinked principles:
While the agronomic principles of CA are broadly applicable, their practices for implementation are to be locally formulated and adapted to fit the given context. CA is now implemented on roughly 205 million hectares across more than 100 countries, equally distributed in the global North and South.
SRI is a crop management strategy that enhances the growth and performance of rice plants. The interlinked SRI principles are:
Like CA, SRI practices are always to be adapted to local conditions, while the principles are broadly applicable. With appropriate adjustments, SRI principles are beneficial also for other crops such as wheat, maize, sugarcane, and millet, resulting in the System of Crop Intensification (SCI).
Moving SRI practices toward a CA-based farm management addresses critical issues like soil disturbance, lack of soil cover and limited species diversity in rice paddies. Although SRI practices constitute a big step forward in terms of productivity and sustainability compared to conventional rice farming, the majority of SRI farmers still prepare their field by ploughing and puddling the soil. Also, SRI does not maintain permanent biomass cover on the soil as rice monoculture leaves the ground bare between seasons and does not promote species diversity in rice paddies. Despite these factors, combining CA with elements of SRI is not only possible, but desirable, and it already proves effective in multiple countries.
One of the most common strategies to replace soil puddling is by practising no-till, direct-seeded rice (DSR). This involves placing rice seeds directly into untilled soil rather than growing seedlings in nurseries and then transplanting them into puddled-flooded fields. Coupling no-till DSR with the SRI principle of reducing plant density, to minimise plants’ competition for water, nutrients, and sunlight, enables the development of larger canopies and deeper root systems.
In a CA system, the management of water is similar to that in SRI, maintaining the soil in a mostly moist condition with no continuous inundation. In both CA and SRI, the aim is to nurture the abundance and diversity of soil organisms and promote healthier, more active root systems. Larger, more robust root systems better tolerate water stress, improve water-use efficiency, and reduce plant lodging due to the stronger anchorage in the soil. In irrigated areas, alternate wetting and drying (AWD) is the preferred water management while there are examples of appropriate adaptations to the management of water in rainfed areas. The improved soil drainage lowers methane (CH4) emissions and the reduced application of nitrogen fertiliser resulting from the CA soil management contributes to lower nitrous oxide (N2O) emissions.
Maintaining a permanent biomass soil cover aligns well with the SRI principle of keeping the soil in aerobic conditions. Rice straw and stubble biomass are an abundant source of organic matter, but the widespread practice of burning them after harvest prevents the return of important elements to the soil and it has a heavy environmental, economic, and health cost. In a CA+SRI system the rice crop biomass is a valuable source of plant nutrients and carbon, as well as a means for integrated weed, nutrient, and insect pest management. This gives farmers an economic incentive to stop burning their straw.
If the layer of mulch is thick enough to cover the soil surface and prevent sunlight from reaching the soil, the germination of weeds is inhibited. This interacts with the CA practices of no-till and crop diversification that contribute to reducing weed occurrence. The effectiveness of straw mulch for controlling weeds is of great importance in a production system where farmers may be concerned that the aerobic soil conditions and increased spacing between plants could encourage weed growth.
Irrigated rice is conventionally raised as a monoculture, in large part because the conventional practice of flooding rice fields does not offer many options for growing associated crops. Under CA+SRI management, anaerobic soil conditions are avoided and the wider spacing between plants makes intercropping and other forms of mixed cropping more feasible. The integration of multi-purpose cover crops into crop rotations or associations can add significant amounts of organic matter to the soil system, concurrently avoiding bare soil and enhancing biodiversity.
- In Pakistan, Punjab, the PQNK system adopted by tens of thousands of farmers combines SRI and CA with organic farming as an overarching framework. Rice is grown on permanent raised beds with biomass mulch, and furrow irrigation. Thanks to the adapted machinery, PQNK is implemented on medium- and large-scale farms which benefit from increased yields, greater income, reduction of water requirements, and improved crop resilience.
- In Arkansas, USA, an innovative farmer combines CA and SRI methods for large-scale, mechanised rice production using no-till raised, mulched beds and furrow irrigation. Two rows of plants are established on each bed 40 cm apart, maintaining 15 to 20 cm between plants on the same row. This reduces the seeding rate from 28 kg ha-1 to around 5.5 kg ha-1, resulting in greater profit.
- In Maharashtra, India, the Saguna Regenerative Technique (SRT) blends CA with SRI principles, promoting direct-seeded rice on no-till raised beds and crop rotation.
- Madagascar initiated a merger of CA and SRI in 2011. More recently, the Aga Khan Foundation developed an innovative package of sustainable agriculture techniques called the Zanatany Rice Permaculture System (ZRPS). The method is being disseminated in Mozambique, India, Kenya, and Tanzania. ZRPS is based on the direct seeding of rice combined with the local production and use of 100% natural inputs for soil fertility and crop protection, overlapping crop rotations, permanent soil cover, minimum soil disturbance, reduced plant density, aerobic soil conditions, and increased soil organic matter.
Of the more than 160 million hectares of rice cultivation worldwide, only a small portion currently embrace sustainable practices such as AWD, DSR, and residue management. Even fewer rice farmers operate within integrated farming systems that encompass aspects like water, soil, crop, nutrients, residues, pest control, labour, and energy management. Shifting from traditional rice farming to a CA-based rice production approach that incorporates SRI principles provides an opportunity for rice-producing countries to boost yields, improve farmer livelihoods and food security while mitigating the environmental challenges associated with rice cultivation.
Look at the recently published peer-reviewed article ‘Compatibility between Conservation Agriculture and the System of Rice Intensification’ for more detailed information on this topic!