Paddy Fields in a Globalized World 2: Methane

Methane. A powerful greenhouse gas; human activities pump it out like crazy. By now educated readers are aware of the problem of methane from production of cattle and other ruminants, which worldwide accounts for 28% of methane production (EPA). Last year, I wrote a post on paddy fields in a globalized world and learned that rice paddy fields, 90% of which are in Asia, account for roughly 20% of global methane production according to most sources, though there is much variability in the estimates. They are also known to be major producers of another greenhouse gas, nitrous oxide.

The connection between human activities and a warming world, robustly-established in the climate sciences, is important because by 2050 the world will be feeding 9 billion people, meaning that rice production and its associated methane production will likely have to increase.

In Taiwan rice is generally planted twice a year. The vast majority of methane emissions take place during the second planting (here, here). Because in every country cropping practices are different, local factors affect methane output from rice farming. This paper on the methane emissions in all 15 of Taiwan's irrigation districts observes:

The amount of methane emitted in the second crop season was 7– 16 times that emitted during the first crop season. If the reduction in planted acreage proposed (12%) is during the second crop season, this will reduce the amount of methane emitted by 21% annually.

Additionally, the rice straw following the first crop harvest is ground into the soil before the rice is planted in the second crop season. The addition of ground rice straw to the soil significantly increases the rate of emission of methane in the hot and humid summer. Removing the rice straw from the soil greatly reduces the rate of emission of methane.

The authors recommend that rice straw be removed from fields prior to the second planting to reduce methane emissions. The paper dates from 2003, when Taiwan had just entered the WTO and the government had taken thousands of hectares of rice fields out of production to comply with agreements to import rice. This ironically reduced methane emissions. The paper observes that in Taiwan temperature is the major determinant of rice field methane output; it is highest in Pingtung fields and lowest in Nantou.

Another factor in rice field methane output is water and water depth. In China methane emissions fell 40% when water-saving practices were implemented that drained fields of their water three times annually instead of keeping them continually flooded. In Taiwan the effects are similar though not so dramatic. This is because when the fields are flooded, soil bacteria shift to anaerobic fermentation of organic material in the field, which creates methane. Upland rice fields, which are not flooded, produce negligible amounts of methane. Recall, however, that as my post on paddy fields noted, flooding rice fields recharges underground water sources.

Another methane reducer in Asia was the shift to artificial fertilizer and away from animal and organic waste. Differences in fertilizer type also affect methane production. Nitrogen-rich fertilizers result in much higher methane emissions, in one 2003 study in Taiwan large reductions were found if non-nitrogen fertilizers were used (another study of methane and nitrous oxides emissions from Taiwan).

Because every region has its own special methods and practices for producing rice, there is no global fix for the problem of methane production from rice fields. But it is surely something humanity will have to consider in the coming decades.

REF: Want to reduce weeds, snails and methane in rice paddies? Try ducks!
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Paddy Fields in a Globalized World

The Taipei Times ran a really great commentary today on the many benefits of paddy fields by Chan Shun-kuei, who heads up the environmental committee of the Taipei Law Association. It paints a beautiful portrait of the positive externalities of paddy fields, which account for just over half of the cultivated farmland in Taiwan:

Most think that growing rice in paddy fields uses up a lot of water and is of little economic benefit, and that devoting more land to rice would put Taiwan’s water supply under greater strain. That may be true under the current short-term conditions, but in the long term, paddy fields actually do not use a lot of water. On the contrary, they are an efficient way of circulating water.

Apart from the private benefit gained by farmers harvesting rice, paddy fields are beneficial for the whole nation. Research conducted in Taiwan and abroad confirms that paddy fields help regulate floodwater and replenish groundwater. The reservoir ponds that dot Taiwan’s countryside contribute to this effect. Other benefits of paddy fields include beautifying the environment, purifying water, regulating the temperature and generating oxygen.

....

In 1993, Tsai Ming-hua (蔡明華), now director of the council’s Department of Irrigation and Engineering, carried out research into the beneficial effects of paddy field irrigation. He found that, between 1982 and 1992, the reduction of land devoted to paddy fields caused Taiwan to lose 13.473 billion tonnes of groundwater that would otherwise have been replenished through paddy field irrigation — roughly 23 times the storage capacity of the Zengwen Reservoir (曾文水庫).

Fighting drought in the short term may require extraordinary means, but water resources also need to be planned over the long term. Consumption can be reduced through pricing, by charging higher, differential and progressive rates for water use. Replacing old pipes would reduce leakage. Domestic and industrial wastewater can be recycled and reused. Existing reservoirs should be preserved wherever possible. Soil and water in reservoir catchment areas could be conserved by preventing unauthorized farming and construction.

Proper care should be taken of farmers and the land. Putting fallow fields back into production would make Taiwan more self-sufficient in food, and it would also replenish groundwater, forming a natural reservoir. As well as regulating the water supply, this would reduce the problem of land subsidence. To do so would have many advantages, since it would cost less and have a smaller environmental impact than building more reservoirs, artificial lakes or desalination plants.

The author points out that the actual amount of water used to grow the crops is tiny, the rest returns to circulation, including helping to replenish groundwater resources that benefit everyone. In addition to stopping subsidence and providing continued flows of groundwater, this paper observes that paddy field water also raises the local water tables, benefiting local flora. In fact, the author argues that "conserving water" during wet months is counterproductive:

Thus, from the viewpoint of effective utilization of water resources, it is meaningless to save water during wet months. On the contrary, if the excess water is available in rivers, it should be timely delivered to the paddy field to enhance the storage function of the paddy field, maintain adequate percolation and replenish ground-water, without having to follow the strict water conservation measures.

Experiments on using paddy fields to artificially recharge groundwater were conducted in Taiwan beginning in the 1980s (for example). The author also advocated over-irrigation as a way to replenish lost groundwater on the Changhua plain. Severe subsidence continues, however.

Paddy field water effects are so powerful that as rice imports drive paddies out of business, this author argued for converting fallow fields into wetlands to preserve their important externalities for the island's water circulation: wildlife benefits, groundwater replenishment, and flood mitigation. Sadly, it seems unlikely that anything so rational will occur.

Rice paddy field areas in Taiwan (source). How many of you would have guessed that Taoyuan has more paddy fields than Pingtung?

In Taiwan the government runs a set-aside program for farmland under which large quantities of farmland lie fallow. In some years the amount set aside exceeds the amount planted in rice (!). This program has come under much criticism, since sometimes farmland becomes unusable after being set aside and land lying uncared for invites pests that affect nearby farms. This results in abandoned land, 50,000 hectares by one 2004 estimate. When land leaves the market, it drives up the price of remaining land, pushing up rents -- and many farmers are renters, not owners. Further, for many observers it makes little sense to set aside good farmland in the lowlands while permitting farming on slopes. The set aside program is also driven by shortages of water, diverted for industrial and residential needs. Everything is exacerbated by the lack of government oversight and monitoring, a persistent problem in all areas of government policy in Taiwan.

Paddy fields have other important benefits that Chan's piece was too short to mention. This paper observes that paddies cool the air around them, saving electricity:

When water evaporated from the ponding surface of paddy, it takes up heat from surrounding air, lowering the air temperature, especially in the summer. Using the thermal band of Landsat 7 satellite image, Tan (2004) has shown a 7.81 C temperature difference between paddy field and urban land cover. To evaluate the air-cooling effect, Wu (2003) shown that the net electric power saving of rice paddy is 4,497 unit power/ha/day.

Rice paddies also purify water and release oxygen. Their single negative environmental effect is methane emissions, methane being 20 times more powerful a greenhouse gas than carbon dioxide. The IPCC estimates that 20% of total global methane emissions are from rice paddies.

One study looked at the total external benefits of rice paddies in two agricultural plains in Taiwan. It calculated:

Moreover, the internal value of rice production ranges from 1.332 to 1.886 billion NT$ and the
external value of rice paddy ranges from 5.836 to 9.851 billion NT$ in the Ping-Tung plain.

The internal value is basically what you can sell the rice for, while the external value represents the benefits to the local ecology as a whole.

Such values should spark thoughtful contemplation of the poverty that imperils many rural communities in Taiwan: as their paddies are taken out of production or converted to factories and cookie-cutter housing developments, many positive externalities that raise living standards and local incomes are lost. For this reason some academics have proposed a green subsidy for farmers because paddy field benefits are so economically important and externally beneficial.

The importance of paddies in local environmental and water regulation also raise the issue of farm subsidies in global trade agreements, the impoverished and destructive way "competitiveness" is defined, as well as the actual cost of importing agricultural goods. From the ecological perspective farm subsidies may just be one way society can return to the farmer some of the benefits the farmer gives all of us, while the loss of groundwater, flood control benefits, local cooling, wildlife, and continued subsidence are some of the hidden costs of the globalization and commodification of agricultural products that don't show up in the lower prices of imported goods, and are not recouped by local society in its interaction with global trade networks.
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