China’s Soils Ruined by Overuse of Chemical Fertilizers
Cropland soils are turning acid from the
overuse of nitrogen fertilizers, decreasing productivity, polluting the
environment, and contributing huge amounts of greenhouse gas emissions; researchers
recommend reducing fertilizer use, but have not considered phasing it out
altogether by adopting organic agriculture Dr. Mae-Wan Ho
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Intensive chemical agriculture turns
There has been a significant decline in
soil pH since the 1980s in China’s major croplands, mainly from the overuse of
nitrogen fertilizers. 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 .
acidification will threaten food security and environmental safety worldwide,”
Zhang said . “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.”
recommend optimal nutrient-management strategies that can significantly reduce
nitrogen fertilizer rates without compromising crop yield, but have not
considered adopting organic agriculture and phasing out nitrogen fertilizers
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; it is approximately equal to the negative
logarithm (base 10) of the hydrogen ion (H+) concentration.)
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 percent of the world’s ice-free land and are
commonly associated with phosphorus deficiency, aluminium toxicity, and reduced
biodiversity and productivity.
agriculture has intensified greatly since the early 1980s on a limited land
area with large inputs of chemical fertilizers. Grain production and fertilizer
nitrogen consumption reached 502 Mt and 32.6 Mt respectively in 2007, increasing
54 and 191 percent since 1981. High levels of N fertilizer 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 fertilizer inputs compared with
other agricultural systems worldwide, especially cash crops like greenhouse
vegetables that have expanded rapidly since the 1980s.
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). As the scale is
logarithmic, a pH decrease of 0.3 corresponds to a doubling in hydrogen ion
Soils in group 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
Acidification of Chinese soils
Overuse of nitrogen fertilizers largely
These broad comparative results are
corroborated by data from 154 agricultural fields in which strictly paired
measurements from the same sites in the 1980s and the 2000s are available. The
average decline in pH in these sites is well over 0.5.
Yet more data
from 10 long-term monitored field sites in which soil pH was measured regularly
over 8 to 25 years also showed decreases in pH ranging from 0.45 to 2.20, only
in NPK fertilized plots and not in unfertilized soils, or soils with no crop
In the three major Chinese
double-cropping systems – wheat-maize, rice-wheat, and rice-rice – annual N
fertilizer application rates are usually above 500 kg N/ha, with nitrogen
efficiencies of only 30 to 50 percent. (Nitrogen use efficiency is generally
defined as production or carbon fixation per unit nitrogen taken up.) In these
systems, ammonium and nitrate N indicate that N loading contributes to
increasing 20 to 33 kmol H+/ha/year. Greenhouse vegetable systems,
the major cash crops, receive even greater N fertilizer inputs. In Shandong province, N fertilizer rates above 4 000 kg N/ha/y are common, with N use
efficiency well below 10 percent. Under this management, about 220 kmol H+/ha/y
accumulates. The proton (H+) generation related to N – 20 to 221
kmol/ha/y – in China is extremely high compared with values of 1.4 to 11.5
kmol/ha/y associated with the lower N fertilizer rates in other countries.
Plant uptake of base
cations (positively charged metal ions), which are then removed as harvests
from fields, also leads to soil acidification because it leaves behind excess anions
(negatively charged ions) that are balanced by an equivalent amount of H+
released to the soil. Currently, about 25 tonnes of dry biomass are harvested
annually in the three double-cropping systems, resulting in an estimated release
of 15 to 20 kmol H+ /ha/y 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 fertilizers and base cation removal is 30 to
50 kmol H+/ha/y for cereal systems, and 230 kmol/ha/y for greenhouse
vegetable systems. In comparison, acid deposition due to acid rain is negligible,
at 0.4 to 2.0 kmol/ha/y.
Each kg of
applied ammonium-N leached as nitrate-N requires 7.2 kg of CaCO3 to
neutralize, which is very expensive.
Nitrogen fertilizers pollute the
environment and increase greenhouse gas emissions
Soil acidification occurs not just in
China, but wherever and whenever intensive chemical fertilization agriculture
is practiced in response to pressures to produce more food, and recently,
bioenergy crops for biofuels  Biofuels:
Biodevastation, Hunger & False Carbon Credits (SiS 33), which
means even less land for growing food in developing countries.
Keith Goulding and David Powlson of UK’s Rothamsted Research Institute
highlight another important aspect of chemical fertilization : "The impact of N fertilizer over-use on greenhouse gas emissions
is often overlooked. It arises through the carbon dioxide emitted when
manufacturing fertilizer, and nitrous oxide, a powerful greenhouse gas, emitted
when N fertilizer is applied to soil. Our work with Chinese collaborators shows
that reductions in N use of 30 percent 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 fertilizer 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 fertilizers altogether in favour of organic fertilizers  (see Sustainable Agriculture, Green Energies and the Circular
Economy, SiS 46).
caglar Comment left 9th May 2010 21:09:16 I am a farmer and growing vegetables to sell. For more efficency i use fertilizers but while using them it is important to
keep it healthy because some fertilizers contain corruptive elements so i try to read everything about fertilizers and try
to keep my product healthy. I am grateful for those who gives information about fertilizers and anyone who
uses fertliziers should read about it, i also found another good guide which should be read too i think;
Jeffrey Michel Comment left 30th March 2010 14:02:40 Excessive coal usage is probably compounding this problem. Here in eastern Germany, the use of high-sulphur lignite had measurable effects on plant growth. Some streams became so acidic that trout could no longer spawn. Automobile emissions, arising largely in western Germany and falling on local cultivated fields were calculated to be equivalent to the amount of artificial fertlizer that German farmers used in the 1930's.
Paulo Ramos Comment left 30th March 2010 14:02:22 It is a very important information which doesn´t get most farmers that are also victims of bad technical assistance. The promisses of production!
I would like to have more detailed informations about the processes by wich Nitrogen based fertilizers or wild fire retardants turn soils acid and the implications for the atmosferic concentrations of NO2 for example.
Mae-Wan Ho Comment left 31st March 2010 17:05:02 The most important acid forming reactions for N fertilizers is microbial oxidation of ammonium compounds and urea to nitrate, especially when it N fertilizers are added in excess of what the plants can assimilate.
NH3 + 2O2 → H+ + NO3- + H2O
The most important acid forming reactions for N fertilizers is microbial oxidation of ammonium compounds and urea to nitrate, especially when it N fertilizers are added in excess of what the plants can assimilate.
NH3 + 2O2 → H+ + NO3- + H2O
The most important acid forming reactions for N fertilizers is microbial oxidation of ammonium compounds and urea to nitrate, especially when N fertilizers are added in excess of what the plants can assimilate.
NH3 + 2O2 → H+ + NO3- + H2O
CO (NH2) + 4O2 → 2H+ + 2NO3- + H2O + CO2
It is the protons (H+) generated in the nitrification reaction that causes acidity.
When plants assimilate nitrate, i.e., when they take up the nitrate and react it with an organic compound (R-OH) they consume protons, as follows:
R-OH + NO3- + H+ → R- NH2 + O2
So if nitrogen is in balance, there should be no acidification of the soil.
Rory Short Comment left 31st March 2010 17:05:47 Our arrogance as a species is appalling and will no doubt lead to our disappearance. A little knowledge is a dangerous thing and the current situation with regard to the processes of life is that we still have insufficient knowledge to be confident of the outcomes when meddling with them.
Santhanam R. Comment left 30th March 2010 14:02:55 Well one got the impression that China was the role model to follow especially after the self declaration that China will become fully organic in a few years?
The earthworm gut can make soils richer, reduce acidity. Other is to use stabilised bio solids from segregated MSW and apply them to farm lands instead of dumping in land fills , emitting GHG.
Two technologies from India can help achieve these: Biosanitizer and Vrikshayurveda a Vedic sciences based proprietary knowledge based farming.
lewse bitch 101 Comment left 14th March 2011 11:11:24 look there are no effects displayed here and effects are just as important as the problem