'White revolution' to 'white pollution' - Agricultural plastic film mulch in China

Abstract

Plastic film mulching has played an important role in Chinese agriculture due to its soil warming and moisture conservation effects. With the help of plastic film mulch technology, grain and cash crop yields have increased by 20–35% and 20–60%, respectively. The area of plastic film coverage in China reached approximately 20 million hectares, and the amount of plastic film used reached 1.25 million tons in 2011. While producing huge benefits, plastic film mulch technology has also brought on a series of pollution hazards. 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. To control pollution, the Chinese government urgently needs to elevate plastic film standards. Meanwhile, research and development of biodegradable mulch film and multi-functional mulch recovery machinery will help promote effective control and management of residual mulch pollution.

Full text

Perspective
‘White revolution’to ‘white pollution’—
agricultural plastic film mulch in China
E K Liu
1,2,3
,WQHe
1,2,3
and C R Yan
1,2
1
Institute of Environment and Sustainable Development in Agriculture, Chinese Academy of Agricultural
Sciences, Beijing 100081, People’s Republic of China
2
Key Laboratory of Dryland Agriculture, Ministry of Agriculture of the People’s Republic of China
(MOA), Beijing 100081, People’s Republic of China
E-mail: yancr@ieda.org.cn
Received 4 July 2014, revised 31 July 2014
Accepted for publication 1 August 2014
Published 9 September 2014
Abstract
Plastic film mulching has played an important role in Chinese agriculture due to its soil warming
and moisture conservation effects. With the help of plastic film mulch technology, grain and cash
crop yields have increased by 20–35% and 20–60%, respectively. The area of plastic film
coverage in China reached approximately 20 million hectares, and the amount of plastic film
used reached 1.25 million tons in 2011. While producing huge benefits, plastic film mulch
technology has also brought on a series of pollution hazards. 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. To control
pollution, the Chinese government urgently needs to elevate plastic film standards. Meanwhile,
research and development of biodegradable mulch film and multi-functional mulch recovery
machinery will help promote effective control and management of residual mulch pollution.
Keywords: agricultural plastic film, white pollution, control pollution
In the past 30 years, advancement in agricultural science and
technology has caused great changes in agricultural produc-
tion in China [1]. Plastic film mulching technology has
remarkably improved grain crop yield and water use effi-
ciency through conserving water, maintaining soil moisture,
suppressing weeds, increasing temperature and improving
cold tolerance. Nationwide, the technology has led to a
20–35% increase in grain crop yield and a 20–60% increase in
cash crop yield. Maize, wheat, cotton and potato yields have
increased by 33.7%, 33.2%, 26.1% and 36.7%, respectively,
while their corresponding water use efficiency levels have
increased by 38.9%, 30.2%, 30.2% and 37.8%, respectively
[2]. At present, transformation of Chinese agriculture aims to
establish an intensive, standardized, mechanized, indus-
trialized and specialized modern agriculture system. In this
regard, plastic film mulching technology plays a crucial role
in enhancing regional agricultural production, ensuring food
security and increasing income of farmers.
According to China Agricultural Statistical Yearbook [3],
the volume of plastic film mulch used in China increased
nearly four-fold from 319 000 tons to 1 245 000 tons from
1991 to 2011. Its annual growth rate is 7.1% and is expected
to increase in the coming years. Accordingly, the total crop
area covered with plastic film mulch similarly exhibited a
sustained rate of growth, increasing from 117 000 hm
2
in
1982 to 4 909 000 hm
2
in 1991 to 19 791 000 hm
2
in 2011.
Data from 1991, 2001 and 2011 were analyzed, and the
distribution of plastic film mulch use intensity in China was
calculated as follows: plastic film mulch use intensity =
amount of plastic film mulch usage/regional arable land area.
Over the past 20 years, all of the provinces and regions of
China have shown increasing trends in plastic film mulch use
Environmental Research Letters
Environ. Res. Lett. 9(2014) 091001 (3pp) doi:10.1088/1748-9326/9/9/091001
3
These authors contributed equally to this work.
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intensity, with increase ranging from three- to ten-fold. The
Northern regions exhibited greater growth, with higher
absolute intensity. For example, the plastic film mulch use
intensity in Xinjiang increased from 7.0 kg hm
−2
in 1991 to
34.8 kg hm
−2
in 2011(1 kg plastic film can cover 150–250 m
2
area). Over the next ten years, the cultivation area covered by
plastic film mulch is expected to increase at a rate of 8–10%,
with the covered crop area increasing from the current 20
million hm
2
to above 30 million hm
2
and plastic film mulch
usage increasing from the current 1.2 million tons to above
two million tons.
Despite benefits of plastic film mulch technology, how-
ever, its widespread use has generated large amounts of
mulch residue. As a result, the application of plastic film
mulch technology is evolving from ‘white revolution’to
‘white pollution’(figure 1). Since plastic film mulch is mainly
composed of polyvinyl chloride, the residual mulch film does
not readily degrade in soil. The problem is worsened by the
low rate of plastic film mulch recovery due to mechanized
cultivation and thin film (less than 0.008 mm). Investigation
of the major plastic film mulch use areas in China indicated
soil residual mulch levels of 50–260 kg hm
−2
in arable lands
with long-term plastic film mulch cover (over ten years) [2].
Large amounts of residual mulch film can lead to unsustain-
able farmland use and thereby affect the agricultural envir-
onment [2,4]. The main considerations are as follows. (1)
Effect on moisture and nutrient transport in soil. These
changes primarily reflect the damage to the physical structure
of soil by residual mulch, which blocks the infiltration of
capillary water and natural water and affects the moisture
absorption in soil. As a result, nutrient movement speed and
moisture penetration are reduced. (2) Effect on crop emer-
gence and root growth. Studies in Xinjiang showed that
residual plastic film mulch levels of 200 kg hm
−2
in the top-
soil (0–20 cm) affected the emergence rate of cotton seeds and
reduced cotton production by 15%. (3) Secondary salinization
of soil. Studies showed that mulching for 5–20 consecutive
years led to a 122–146% increase in the salt content of the
topsoil. (4) Degradation of polyethylene residual mulch film
is negligible with the possible formation of environmentally
harmful chemical products such as phthalate esters [5], di-(2-
ethylhexyl) phthalate, aldehydes and ketones.
Scientists in China have recognized the hazards from
plastic film mulch pollution and taken measures to address the
problem of residual plastic film mulch. However, due to
technical and economic limitations, it remains difficult to
apply these measures at a large-scale. Residual plastic film
mulch pollution has become a serious issue and needs to be
addressed from aspects of policy, regulation and technology
in an all-round manner. (1) Improve mulch film standards and
the relevant quality control mechanisms to increase mulch
film recovery and enhance mulch film recycling [5]. The
mulch film currently used in China is less than 0.008 mm
thick; in contrast, the mulch film used in the US and European
countries are generally 0.020 mm and in Japan 0.015 mm. In
these countries, the better quality mulch film remains mostly
intact after use, and nearly no residual plastic film mulch is
left in farmland soil after mechanized recovery. (2) Accelerate
development of biodegradable mulch film with reduced pro-
duction cost to replace the mulch film most commonly used at
Figure 1. Plastic film mulching field in Tongchuang, Shaanxi and plastic mulch residue field in Shihezi, Xijiang, China.
2
Environ. Res. Lett. 9(2014) 091001 E K Liu et al

present [6], which is primarily composed of polyvinyl
chloride. (3) Accelerate research and development of light-
weight, simple and multi-functional machinery for residual
mulch film recovery. The key focus should be farm machin-
ery and technical measures that can be used for both regular
farming operations (such as plowing) and residual mulch film
recovery. Thus, highly efficient mulch film recovery should
be achieved without increasing operation cost and burden on
farmers.
Plastic film mulching technology provides good water
retention and warming effects. If residual mulch film pollu-
tion can be effectively controlled in China, the application of
plastic film mulching technology in this country will provide
a useful reference for improving crop yield and water use
efficiency in other similar regions worldwide, particularly in
regions with cold and arid climates.
Acknowledgments
We thank Professor B H So for useful comments. Partial
support came from National Natural Science Foundation of
China (31370522), 12
th
five-year plan of National Key
Technologies R&D Program (No. 2012BAD09B01) and
‘948’project from Ministry of Agriculture (2014-Z6).
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Environ. Res. Lett. 9(2014) 091001 E K Liu et al