Is rice straw accumulation affecting our planet?

31 March 2022 | Yanis Pantoja

It certainly is affecting our planet! 

Rice crop is grown in the cultivable areas of all the six habitable continents except for the ice-covered continent of Antarctica where agriculture is not feasible. It has been a noticeable part of our culture for several centuries with many festivals across the globe celebrating its heavy harvest. Rice is grown in many countries with a gross cultivated area of nearly 160 million hectares. 

Every year, more than 700 million tons of rice straw is produced worldwide1.  Due to the lack of economically viable options, open field burning is the most common practice for straw disposal, releasing large amounts of harmful gases2.  This leads to alarming levels of environmental pollution causing acute respiratory illness; it also represents a tremendous waste of biomass resources 3. Currently, only about 20% of rice straw is used for practical purposes, such as production of biofuels, paper, fertilisers and animal feed, and after harvest most is either burned in situ, incorporated in the soil or used as mulch for the following crop. However, in Vietnam the situation is different.  

Rice straw is a very important as a feedstock material and for the planet. In this article, we will explain why it is important to find different ways to utilise rice straw, especially in biofuel production.  

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What is Rice Straw, and why does it matter? 

Rice straw is a rice by-product, and it is separated from the grains after the plants are threshed either manually, using stationary threshers or, more recently, by using combine harvesters. Asia produces 90% of the world’s rice and, consequently, it is where the bulk of the straw is produced. Straw utilization as a valuable biomass for biotechnological applications has not been taken into consideration in countries such as Vietnam  1 

With the increase of the population around the world, more production of rice is required, and the rice-cropping systems have been intensified. The rapid introduction of combine harvesters constitutes a game changer because of the larger amounts of straw that is left spread out on the field. Manual collection of the straw in the field is unprofitable because of the high labour cost. Incorporation in the soil poses challenges in intensive systems with two to three cropping rounds per year. This is due to the insufficient time for decomposition, leaving the straw with poor fertilization properties for the soil and hindering crop establishment.  

As a result, open-field burning of straw has increased dramatically, despite being banned in most rice-growing countries because of pollution and the associated health issues. Thus, there is a need to develop new technologies to utilize it as a feedstock to produce biofuels and biopower 2. 

Global-rice-straw-burning-zones

Global Rice straw Burning areas, worldwide.

How is Rice Straw used in Vietnam?

In 2014, 13 million tons of rice straw, equivalent to 60% of the total straw in the Mekong River Delta (MRD) region, Vietnam’s largest rice production area, was burned on-site. In 2016, Vietnam was ranked the third rice exporter worldwide, behind India and Thailand. Statistical data shows that Vietnam produced and released an annual average of 54 million tons of rice straw into the environment, between 2010 and 2019 1. A small portion of rice straw is used as feedstock for mushroom production and to feed farm animals. Most of the produced rice straw is either removed from the field, in situ burned, piled, or spread in the field. This is because using rice straw has cost implications (e.g. collection, transportation) which in turn provide a lower incentive compared to the quick earnings obtained from the next crop.  

In Vietnam, the estimated rice straw residue generated in 2018 and 2019 was approximately 44 million tons per year. Son La, Lao Cai, Ben Tre and Soc Trang are provinces in Vietnam that burn between 70-75% of rice residues 2

However, we cannot simply stop burning straw, since there are also some benefits associated with it. The process of on-site burning releases and recycles nutrients to the soil, including fast-reacting silicon (ca. 5–10% of rice-straw mass is silicon). The presence of enough silicon in the soil has been shown to play a beneficial role in mitigating arsenic uptake in rice, by reducing the translocation of arsenic from the soil to rice. A cessation of on-site open rice-straw burning worldwide will likely increase the availability of arsenic uptake in rice, leading to possible higher human dietary arsenic exposure. Therefore, just as it is important to reduce and find alternatives to rice straw burning in the fields, it is also crucial to find way to keep arsenic levels low in rice 3.

Remember:

  • It is very important to note that rice feeds approximately half the world population, so the generation of less rice straw might not be an easy option. 

  • Burning straw waste in open fields is an “easy” choice for farmers worldwide. However, in doing this biomass is lost, and the pollution increases.

  • Its burning in the field causes acute respiratory illness and alarming pollution levels.

  • Worldwide cessation of on-site rice straw burning is implausible due to a lack of enforcement and a large gap between supporters such as, policy makers, environmentalists, and the farmers.

In our article "The vicious cycle of rice straw burning in Vietnam", we describe why the burning of rice straw is a vicious cycle in more detail. It is essential to highlight the importance of developing new technologies to utilize rice straw in the production of biofuels and biopower.  Find out more about how biotechnology is used to convert rice straw into high value products in the following articles: Biorefineries; Bioethanol, a carbon dioxide neutral neutral energy source; Malic acid is part of your daily life

Carey, M. et al. Global Sourcing of Low-Inorganic Arsenic Rice Grain. Expo. Heal. 12, 711–719 (2020).

Minas, A. M., Mander, S. & McLachlan, C. How can we engage farmers in bioenergy development? Building a social innovation strategy for rice straw bioenergy in the Philippines and Vietnam. Energy Res. Soc. Sci. 70, 1–17 (2020)

3 Gummert, M., Hung, N. Van, Chivenge, P. & Douthwaite, B. Sustainable Rice Straw Management. Sustainable Rice Straw Management (2020). doi:10.1007/978-3-030-32373-8