Biodegradable Films: Save Water & Soil
By Dirk Staerke 15 October, 2015
Plastic mulch films help grow crops but pollute the soil. BASF's Staerke on the situation in China & their new film
Agricultural mulch films are plastic films used on the ground, under the root systems of plants, to facilitate crop cultivation. They support water conservation and sustainable water use by limiting weed growth (and thus reducing over-use of pesticides and subsequent contamination of runoff), and especially by retaining soil moisture and heat. Mulch films are a crucial part of water-efficient agriculture, especially in intensively farmed areas such as Xinjiang.
However, conventional mulch films, which are made of polyethylene (PE), can come with a potentially serious cost: the pollution of soil.
By the end of 2014, in Xinjiang alone, more than 47 million mu of farmland were covered with plastic mulch. After 30 years of aggressive use of mulch films and inadequate attention to the problems of film residue, agro-technicians find that the country’s cotton fields have been eroded severely by plastic pollution.
“While producing huge benefits, plastic film mulch technology has also brought on a series of pollution hazards.“
Prof. Yan Changrong, CAAS
“While producing huge benefits, plastic film mulch technology has also brought on a series of pollution hazards. The plastic, which is mostly made of polyethylene, doesn’t degrade in soil. The problem is worsened by the low rate of plastic film mulch recovery due to mechanized cultivation and very thin film. Large amounts of residual plastic film have detrimental effects on soil structure, water and nutrient transport and crop growth, thereby disrupting the agricultural environment and reducing crop production,” says Prof. Yan Changrong, Chinese Academy of Agricultural Sciences. Studies in Xinjiang also show that residual plastic film has affected the emergence rate of cotton seeds and reduced cotton production.
Many mulch films are buried deep in the soil
The recycling rate of mulch films in China is less than two thirds
China consumes 1.42 million tonnes of agriculture mulch films each year. With the wide application of ultra-thin plastic mulch films and the lack of technology and mechanisms for residue recycling, the recycling rate of mulch films in China is less than two thirds.
Currently the PE mulch film residue is at a level of 16 to 28 kg for each mu of land.
Many mulch films are buried deep in the soil, with some rotted to shreds that cannot be collected by hand. Farmers spend a lot of time getting rid of the residual mulch, but their efforts are often in vain due to the increasingly smaller size of the plastic residue. Collection and recycling of plastic mulch films can be expensive and time-consuming.
Mulch films – indispensable for cotton production
Cotton plantations account for more than half of the total agricultural area in Xinjiang, China’s largest cotton-planting region.
“…Xinjiang is the largest cotton and tomato producing area in China. Therefore, sustainable farming in Xinjiang plays an important role in sustainable textile and food chains…”
Daqing Zheng, Senior Vice President, BASF Greater China
China currently accounts for about 30 percent of the world’s cotton output, with only 15 percent of the world’s cotton-growing land. Its unit yield was 85 percent higher than the world average. All cotton plantations in Xinjiang involve film mulching.
“China is the world’s largest producer of cotton and one of the world’s three main tomato production and processing bases, while Xinjiang is the largest cotton and tomato producing area in China. Therefore, sustainable farming in Xinjiang plays an important role in sustainable textile and food chains in China and globally,” says Daqing Zheng, Senior Vice President, BASF Greater China.
Biodegradable films – a non-polluting alternative
At the Xinjiang Ecological Agriculture Development Summit held in Urumqi held in August, BASF presented updates on ecovio® biodegradable mulch film applications in corn, tomato and potato fields, as well as its achievements in cotton fields.
ecovio® is the name for a range of easy to use, custom tailored, biodegradable compounds, which are partially based on renewable raw materials. ecovio® consists of the certified compostable PBAT ecoflex® and polylactic acid (PLA), which is can be derived from corn or other sugar generating plants, like tapioca. It is certified compostable worldwide.
ecovio® mulch film biodegrades into water, biomass and a small amount of CO2
ecovio mulch film biodegrades into water, biomass and a small amount of CO2. Compounds of ecovio have been used in Germany, Italy and Japan since 1998. For mulch film applications ecovio has been used predominantly in Europe since 2012. ecovio for mulch film applications have been introduced and tested since 2012 in China.
Biodegradation in soil can vary due to varying natural conditions. Under laboratory conditions used in the OK Soil degradation test ecovio reaches 90% biodegradation after 190 days in soil.
According to the new studies, ecovio biodegradable mulch film has demonstrated its water retaining properties, excellent mechanical properties, insulation, and good resistance to UV radiation, at the same time contributing to equal yield – but with no pollution of soil compared to conventional PE films.
The WVTR (Water Vapor Transmission Rate) of ecovio mulch film is higher compared to PE mulch film when measured in a laboratory, although this difference cannot be directly translated into performance in the field, since mulch film has holes for the plants.
BASF began the largest ecovio trial project in Xinjiang Urghur Autonomous Region covering around a total area of 1,700 mu at end of 2014, together with the local partner Xinjiang Production and Construction Corps.
BASF started trial projects with ecovio on 5 crops in Xinjiang
BASF started trial projects on 5 crops in Xinjiang: cotton 280 mu, corn 820 mu, sugar beet 200 mu, potato 200 mu, pumpkin 200 mu and tomato 5 mu. All of these trials have shown that mulch films made with ecovio® outperform conventional technologies, especially in demanding conditions.
“In Xinjiang, cotton has a long growth period which demands that biodegradable mulch films last for at least 90 days,” says Lv Jun, Head of Agriculture Environment and Sustainable Development Institute, Shihezi Agriculture Science & Technology Research Center.
More work needed to bring biodegradable films to the mainstream
Some films in China are labelled biodegradable but are not
Standards need to be established
Not all “biodegradable” films are equal. Some mulch films found in China are labelled biodegradable, but are not – they have a high PLA content and also high TPA content (56%). Standards for biodegradability in soil need to be established for China.
“For a sustainable future in agriculture in China, the development of standards for biodegradable mulch film, regulation on the minimum thickness for PE mulch film and efficient recovery PE mulch film are the most important tasks”, Prof. Yan says.
The cost of biodegradable mulch film is also higher compared to PE mulch film. However, this does not include the costs of soil pollution and its consequent reduced yield. Further soil remediation cost are generally not taken into consideration when comparing biodegradable mulch film with PE mulch film.
Over the past years, BASF has worked with various stakeholders in China to promote sustainable farming through the use of biodegradable mulch film, including the China Plastics Processing Industry Association, the Chinese Academy of Agricultural Sciences and the National Agro-Technical Extension and Service Centre and the Xinjiang Cotton Institution. Trials are also taking place in Yunnan, Shandong, Jiangxi, and Inner Mongolia.
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