At the moment, the vast majority of rice production is done by flooding the rice fields, and keeping them flooded in standing water for the entire life cycle of the rice. It is done this way because rice is a semi-aquatic plant so it feeds it massive demand of water, protects it against infections, and stops weeds from growing. This way of growing rice ends up emitting massive amounts of methane due to microbes feeding on organic matter as the oxygen levels diminishes in the standing water.
The two main alternatives that have been tried, and are already used are AWD and Furrow Irrigation
AWD (Alternate Wetting and Drying). It still involves flooding the fields, but instead of keeping it flooded, farmers would drain it a few times per season. They would flood the fields to about 5-7cm (2-3 inches) above the soil, and let the water drop to 10-15 cm (4-6 inches) under the surface of the soil. Doing only one of this cycle per season could reduce methane emissions by around 35%. Doing it 3 or 4 times could reduce methane emissions by more than 50%. A farm in Arkansas at which this has been tried has show that they could reduce emissions by over 60%.
This method, while very promising and efficient, is quite difficult to implement in Asia where rice has been domesticated thousands (around 9000) of years ago, and the method of cultivation has seen very little change. It would also be very difficult to implement in mountainous regions where farms are interconnected in steps. Moreover, the rainy season of southeast Asia makes it near impossible as the fields stay flooded even if the farmers stop irrigating the crops.
Furrow irrigation involves planting the rice in rows of dirt mounds, and flooding the channels in between the rows. This allows oxygen in the soil and, in return, reduce the emissions by limiting the decomposition of organic matter. This method is already popular in parts of the U.S.A. where farmers rotate rice and soy crops. Furrow irrigation would also be much easier to implement in mountainous regions than AWD.
In addition to water management, straw management is an other effective strategy. The food the microbes feed on is the straw left by the previous harvest. One way of doing this is to burn the leftover straw (least labor intensive, fastest, cheapest way), but it impacts air-quality significantly, and thus, has non-negligible health consequences. The better options would be to physically remove the straw, but it is much more labor intensive, and thus more expensive. But the straw can be sold to mushroom farmers as a growing medium for the fungi. This could also create work as straw balers would be needed. Straw can actually also be used to create a biodegradable alternative to single-use plastic.
There are a few other options like switching to higher-yields varieties of rice, different soil additives, and using other types (usually more expensive) of fertilizers.
If you are really interested in learning more, these two studies are really interesting, and offer many different water and straw management techniques.
The straw thing is super interesting (all of it is really-- thanks for this explanation). I wonder if there is a way to do in-situ biochar of the straw that isn’t just setting the field on fire.
Yes of sure!
At the moment, the vast majority of rice production is done by flooding the rice fields, and keeping them flooded in standing water for the entire life cycle of the rice. It is done this way because rice is a semi-aquatic plant so it feeds it massive demand of water, protects it against infections, and stops weeds from growing. This way of growing rice ends up emitting massive amounts of methane due to microbes feeding on organic matter as the oxygen levels diminishes in the standing water.
The two main alternatives that have been tried, and are already used are AWD and Furrow Irrigation
AWD (Alternate Wetting and Drying). It still involves flooding the fields, but instead of keeping it flooded, farmers would drain it a few times per season. They would flood the fields to about 5-7cm (2-3 inches) above the soil, and let the water drop to 10-15 cm (4-6 inches) under the surface of the soil. Doing only one of this cycle per season could reduce methane emissions by around 35%. Doing it 3 or 4 times could reduce methane emissions by more than 50%. A farm in Arkansas at which this has been tried has show that they could reduce emissions by over 60%. This method, while very promising and efficient, is quite difficult to implement in Asia where rice has been domesticated thousands (around 9000) of years ago, and the method of cultivation has seen very little change. It would also be very difficult to implement in mountainous regions where farms are interconnected in steps. Moreover, the rainy season of southeast Asia makes it near impossible as the fields stay flooded even if the farmers stop irrigating the crops.
Furrow irrigation involves planting the rice in rows of dirt mounds, and flooding the channels in between the rows. This allows oxygen in the soil and, in return, reduce the emissions by limiting the decomposition of organic matter. This method is already popular in parts of the U.S.A. where farmers rotate rice and soy crops. Furrow irrigation would also be much easier to implement in mountainous regions than AWD.
In addition to water management, straw management is an other effective strategy. The food the microbes feed on is the straw left by the previous harvest. One way of doing this is to burn the leftover straw (least labor intensive, fastest, cheapest way), but it impacts air-quality significantly, and thus, has non-negligible health consequences. The better options would be to physically remove the straw, but it is much more labor intensive, and thus more expensive. But the straw can be sold to mushroom farmers as a growing medium for the fungi. This could also create work as straw balers would be needed. Straw can actually also be used to create a biodegradable alternative to single-use plastic.
There are a few other options like switching to higher-yields varieties of rice, different soil additives, and using other types (usually more expensive) of fertilizers.
If you are really interested in learning more, these two studies are really interesting, and offer many different water and straw management techniques.
water management: https://www.mdpi.com/2073-4395/13/6/1522
straw management: https://www.researchgate.net/publication/356796388_A_Review_on_Rice_Straw_Management_Strategies
Thanks for detailed explanation 👍
The straw thing is super interesting (all of it is really-- thanks for this explanation). I wonder if there is a way to do in-situ biochar of the straw that isn’t just setting the field on fire.