soils ruined by overuse of chemical fertilisers
Cropland soils in China
are turning acid from the overuse of nitrogen fertilisers, decreasing
productivity, polluting the environment, and contributing huge amounts
of greenhouse gas emissions. Researchers recommend reducing fertiliser
use, but have not considered phasing it out altogether by adopting organic
Intensive chemical agriculture
turns soils acid
THERE has been a significant
decline in soil pH since the 1980s in China's major croplands, mainly from
the overuse of nitrogen fertilisers. This was revealed in a study carried
out by Chinese, UK
and US researchers
led by Zhang Fu Suo at the China Agricultural
University in Beijing.1
'Serious soil acidification
will threaten food security and environmental safety worldwide,' Zhang
said.2 'Our work has shown that soil quality or soil health should be
paid more attention in intensive agricultural production systems receiving
high nitrogen and other resource inputs.'
The researchers recommend optimal
nutrient-management strategies that can significantly reduce nitrogen
fertiliser rates without compromising crop yield, but have not considered
adopting organic agriculture and phasing out nitrogen fertilisers altogether.
Soils are strongly buffered
by inorganic ions, by the weathering of soil mineral, and in the acidic
range, by interactions with aluminium and iron, so that its pH remains
relatively constant. (pH is a measure of acidity and alkalinity on a
scale of 0 to 14, 7 being neutral. A pH of less than 7 indicates acidity;
the lower the pH, the greater the acidity. pH is inversely related to
the concentration of hydrogen ions (H+), as a higher concentration indicates
Soils become acid very slowly
under natural conditions, over hundreds to millions of years. Old soils
and soils in high rainfall regions tend to be more acid. Naturally acid
soils occupy approximately 30% of the world's ice-free land and are
commonly associated with phosphorus deficiency, aluminium toxicity,
and reduced biodiversity and productivity.
Chinese agriculture has intensified
greatly since the early 1980s on a limited land area with large inputs
of chemical fertilisers. Grain production and fertiliser nitrogen (N)
consumption reached 502 megatonnes (Mt) and 32.6 Mt respectively in
2007, increasing 54% and 191% since 1981. High levels of N fertiliser
can acidify soils both directly and indirectly, and the rates of N applied
in some regions are very high compared with those of North America and
Europe. This has degraded soils and
environmental quality in the North China Plain and the Taihu
Lake region in south China, traditionally famous for its
scenic beauty but now infamously putrid and polluted.3,4
A national soil survey had
been conducted during the early 1980s, and pH was determined in all
top soils sampled. For comparison, the team collected all published
data on top soil pH from 2000 to 2008 and compiled two (unpaired) datasets
on the basis of six soil groups according to geography, and two subgroups
of cereal crops and cash crops. Both cropping systems receive very high
fertiliser inputs compared with other agricultural systems worldwide,
especially cash crops like greenhouse vegetables that have expanded
rapidly since the 1980s.
The results showed significant
drops in pH of 0.13 to 0.8 except in the highest pH soils, which represent
only a small percentage of Chinese cultivated soils. In all other soil
groups, acidification has been greater in cash crops (pH decreased by
0.3 to 0.8) than cereals (0.13 to 0.76) (see Table 1 on p.5).
Soils in group I (see Table
1) are the most acidic in south China and have acidified further since
the 1980s. Athough the net pH decreases for group I soils were small
compared to the other groups, the impact may be more pronounced because
these soils are approaching acidity at which potentially toxic metals
such as aluminium and manganese could be mobilised.
Overuse of nitrogen fertilisers
largely to blame
The results are backed up by
data from 154 agricultural fields in which they measured the same site
in the 1980s and in the 2000s. The average drop in pH in these sites
is well over 0.5.
Still more data from 10 field
sites in which soil pH was measured regularly over a period of 8 to
25 years also showed decreases in pH ranging from 0.45 to 2.20, and
only in chemically fertilised plots, not in unfertilised soils, or soils
with no crop planted.
In the three major Chinese
double-cropping systems - wheat-maize, rice-wheat, and rice-rice - annual
N fertiliser application rates are usually above 500 kg N/ha. These
systems contribute to increasing hydrogen ion concentration (i.e., acidity)
by 20 to 33 kilomols (kmol)/ha/year. Greenhouse vegetable systems, the
major cash crops, receive even greater N fertiliser inputs. In Shandong province, N fertiliser rates above
4,000 kg N/ha/year are common. Under this management, about 220 kmol
H+/ha/year accumulates in the soil. The proton (H+) generation related
to N in China
is extremely high compared with other countries with lower N fertiliser
Plant uptake of base cations
(positively charged metal ions), which are then removed as harvests
from fields, also leads to acid soils because the cations are replaced
by hydrogen ions. Currently, about 25 tonnes of dry biomass are harvested
annually in the three double-cropping systems, resulting in an estimated
release to the soil of 15 to 20 kmol H+/ha/year that compensates for
the base cations removed. In the greenhouse vegetable systems, the importance
of base cations uptake varies greatly with plant species and yield but
overall appears similar to the cereal systems.
Thus, the total H+ added to
the soil due to nitrogen fertilisers and base cation removal is 30 to
50 kmol H+/ha/year for cereal systems, and 230 kmol/ha/year for greenhouse
vegetable systems. In comparison, acid deposition due to acid rain is
negligible, at 0.4 to 2.0 kmol/ha/year.
Nitrogen fertilisers pollute
the environment and increase greenhouse gas emissions
Soil acidification occurs not
just in China,
but wherever and whenever intensive chemical fertilisation agriculture
is practised in response to pressures to produce more food and, recently,
bioenergy crops for biofuels,5 which means even less land for growing
food in developing countries.
The overuse of chemical fertilisers
is a major source of environmental pollution from agriculture, which
China’s recent national pollution census identified to be a greater
pollution source than industry (see article next page).
Collaborating scientists Keith
Goulding and David Powlson of the UK’s
Rothamsted Research Institute highlight another important aspect of
chemical fertilisation:6 ‘The impact of N fertiliser overuse on greenhouse
gas emissions is often overlooked. It arises through the carbon dioxide
emitted when manufacturing fertiliser, and nitrous oxide, a powerful
greenhouse gas, emitted when N fertiliser is applied to soil. Our work
with Chinese collaborators shows that reductions in N use of 30% and,
in some cases, much more are possible without any threat to China’s food security, and would make a significant
contribution to reducing total greenhouse gas emissions from China.
Avoiding N fertiliser over-use is a "multiple win": farmers
save money, there is less water pollution, smaller greenhouse gas emissions,
and a smaller acidification burden on soil and water.’
The real solution is to phase
out chemical fertilisers altogether in favour of organic fertilisers.7
Dr Mae-Wan Ho is Director
and co-founder of the UK-based Institute of Science in Society <www.i-sis.org.uk>,
Editor of Science in Society magazine and scientific adviser to the
Third World Network. The above is an edited version of an article published
in Science in Society (No. 46, Summer 2010).
1. Guo JH, Liu XJ, Zhang
Y, Shen JL, Han WX, Zhang WF, Christie P, Goulding KWT, Vitousek PM
and Zhang FS. ‘Significant acidification in major Chinese croplands’.
Science 2010, 327, 1008-10.
2. 'Nitrogen fertiliser acidifies
soils in China', environmentalresearchweb,
17 February 2010, http://environmentalresearchweb.org/cws/article/research/41738
3. Ma J. ‘Disaster in Taihu
8 June 2007, http://www.chinadialogue.net/article/show/single/en/1082-Disaster-in-Taihu-Lake\
4. Yang S-Q and Liu P-W.
'Strategy of water pollution prevention in Taihu Lake
and its effects analysis'. Journal of Great Lakes
Research 2010, 36, 150-8.
5. Ho MW. ‘Biofuels: biodevastation,
hunger & false carbon credits’. Science in Society 33, 2007.
6. Rothamsted Research. ‘A
30% cut in fertiliser use in China
would not threaten food security’, 17 February 2010, http://www.bbsrc.ac.uk/media/releases/2010/100217-cut-in-fertiliser-use-in-china.aspx
7. Ho MW. ‘Sustainable agriculture,
green energies & the circular economy'. Science in Society 46, 2010.
pollution census triggers green five-year plan
is poised to launch a green five-year plan as a national census
finds wastewater runoff from farms to be a far greater source
of pollution than industry.
Census reveals major
pollution from farms
CHINA’s first nationwide
pollution census just completed finds 30.3 million tonnes of pollutants
(chemical oxygen demand, COD) discharged into water in 2007, more
than double the 13.8 million tonnes reported that year. The census
included, for the first time, measurements of wastewater runoff
from farms using chemical fertilisers and pesticides, which accounted
for 13.2 million tonnes of COD. The report, which mapped data
from 5.9 million sources, showed that China
discharged about 209 billion tonnes of wastewater and 63.7 trillion
m3 of waste gases in 2007.
The main water pollutants
were 1.73 million tonnes of ammonia nitrogen, 900 tonnes heavy
metals, 4.73 million tonnes nitrogen, and 423,000 tonnes phosphorus.
Other pollutants included:
Sulphur dioxide emissions,
23.2 million tonnes
Nitrogen oxides, 17.98
Dusts, 19.21 million
Soot, 11.7 million tonnes
Solid waste, 3.8 billion
tonnes (of which 45.7 million tonnes hazardous)
Livestock faeces, 243
Livestock urine, 163
Plastic film on cropfields,
121,000 tonnes (80.3% recycled).
Wang Yanliang of the
ministry of agriculture acknowledged the high contributions from
intensive livestock farming and excessive use of fertilisers and
pesticides in the fields.
That is due to the immense
size of China's
agricultural sector and the country's massive dependency on artificial
China uses only 7% of the world's
land to feed 22% of its population. (According to a recent Greenpeace
report, the country consumes 35% of the world's nitrogen fertiliser.)
Wang said the ministry would improve the efficiency of pesticide
and fertiliser use, expand biogas generation from animal waste,
which it has already supported in successive five-year plans,1
and change agricultural lifestyles to protect the environment.
The extent of agricultural
waste could prove a larger problem than the many factories dumping
pollution into China's rivers and lakes because it
is easier to control factories than millions of farms.
Reliance on chemical
farming not necessary
Wen Tiejun, dean of the
school of agriculture and rural development at Renmin University, said his research suggested
that Chinese farmers used nearly twice as much fertilisers as
they need, and the census should be used as a turning point. He
said: 'For almost all of China's 5,000-year history, agriculture
had given our country a carbon-absorbing economy but in the past
40 years, agriculture has become one of the top pollution sources.
Experience shows that we don't have to rely on chemical farming
to resolve the food security issue. The government needs to foster
Indeed, Chinese peasants
have farmed sustainably according to the circular economy of nature,
as, for example, in the circular economy of the dyke-pond system2
that, in its heyday, supported 17 people per hectare without using
fertilisers and pesticides.
The pollution report
comes at an opportune time as the country's 11th five-year plan
(2006-2010) is drawing to a close, and officials are preparing
the groundwork for the 12th five-year plan. Environmental protection
is given the top priority.
The new five-year plan
aims to reduce carbon intensity - carbon emissions per unit of
GDP - by up to 45% by 2020, when 15% of its energy use will be
non-fossil fuel. It also aims to reverse deforestation by increasing
the total forest cover by 40 hectares and increasing the total
forest stock volume by 1.3 billion m3.
The plan will set specific
targets for different economic regions of China
and will become domestic law, so firms will be legally required
to meet the emission reduction targets. Some experts estimate
that environmental degradation currently costs the Chinese economy
up to 8% of its GDP, so the plan, though painful to firms, is
undoubtedly beneficial for China's long-term economic growth.
The plan is likely to
call for more than $450 billion in investment to protect the environment,
more than double the $219 billion of the 11th five-year plan.
Wastewater treatment companies will be hoping to reap the benefits.
environmental protection industry is reported to be growing at
between 15% and 20% a year. The ministry of environmental protection
has estimated that the production value of the industry will reach
$161 billion in 2010.
to restore 'circular economy agriculture'
What appears to be missing
from the 12th five-year plan is a systems-approach that combines
environmental protection with food and energy production. This
is particularly important as new findings also reveal widespread
acidification of the soil in China's major croplands since the
intensification of agriculture began in the early 1980s, which
is reducing soil productivity.
One approach based on
the anaerobic digestion of livestock and other wastes, already
supported by the Chinese government, is envisaged in a 'Dream
Farm 2', which recreates the circular economy that has served
China so well in the past.3 It uses anaerobic digestion to prevent
pollution by retaining and recycling the wastes into food and
energy resources, while incorporating renewable energies at the
microscale such as wind, solar and hydroelectric, making use of
locally available resources as much as possible.
In our most recent report
on truly renewable and sustainable energies,4 we show it is both
possible and profitable to phase out fossil fuel use altogether
by 2050 for all nations of the world, rich and poor, provided
there is sufficient political will, wisdom, and international
cooperation. - Science in Society (No. 46, Summer 2010)
1. Li KM and Ho MW.
'Biogas China'. Science in Society 32, 2006.
2. Ho MW. 'Circular
economy of the dyke-pond system'. Science in Society 32, 2006.
3. Ho MW. 'Sustainable
agriculture, green energies and the circular economy'. Science
in Society 46, 2010; and Ho MW, Burcher S, Lim LC et al. Food
Futures Now. ISIS and TWN, 2008.
4. Ho MW, Cherry B,
Burcher S and Saunders P. Green Energies: 100% Renewables by 2050.
ISIS and TWN, 2009.
*Third World Resurgence
No. 237, May 2010, pp 2-5