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Inorganic
fertilisers are sometimes the cause for a hot debate. In part this is due to
an incomplete understanding of the need for inorganic fertilisers and in
part it is due to differences in agricultural production between tropical
and temperate regions. Well, I don't want to summarise the debate here and
some developments on the use of inorganic fertilisers are sketched.
Some
historical developments
In
the late 1800s and early 1900s, it was assumed that soil fertility in the
humid tropics must be very high because it supports such abundant
vegetation as rain forest. The American soil scientist E.W. Hilgard
thought that soils of the humid tropics must be rich in humus because of
the abundant vegetation supplying plant material. Continuous and rapid
rock and soil decomposition was thought to be very high under the
prevailing climatic condition, hence providing a constant supply of
minerals for plant growth. The high fertility theory of tropical soils was
dispelled when the forest was cut, crops planted and it was discovered
that yield levels were disappointingly low or rapidly declining. The idea
emerged that soil fertility in the tropics is uniformly low and easily
lost by cultivation. This was substantiated by the fact that travellers in
the tropics noted that soils were lighter in colour and hence assumed that
such soils had lower organic matter contents and chemical fertility. It
was also assumed that many tropical soils would inversely change to
laterites (ironstone) upon cultivation.
Fertiliser
use
After
the Second World War, research emphasis was put on the improvement of soil
fertility by the judicious application of inorganic fertilisers. This
followed the introduction and widespread use of inorganic fertilisers in
the temperate regions. A large number of inorganic fertiliser experiments
was conducted from the 1950s onwards and the experiments focussed on the
search for balanced nutrition, the economics of fertilisers, credit,
subsidies and marketing of fertilisers, and fertiliser training programmes
and extension.
The
increased use of inorganic fertilisers were deemed necessary: (i) to
increase production per unit of land in the face of a growing shortage of
arable land in many developing countries, (ii) to increase marketed food
supplies or exports, and (iii) to raise incomes and return to labour.
Furthermore inorganic fertilisers were needed to make full use of the new
high-yielding varieties. The combined package of new crop varieties, pests
and disease control and the use of inorganic fertilisers caused a dramatic
increase in crop yields in many parts of the tropics. This was particular
the case in Asian countries.
Following
the food production decline in the 1960s, FAO launched in 1961 the Freedom
From Hunger Campaign (FFHC), which was partly financed by the world
fertiliser industry. The FFHC’s main target was to encourage the use of
fertilisers by smallscale farmers through education, effective means of
distribution and credit. The overall idea was that agricultural production
cannot be significantly increased in the developing countries of the world
without improving the nutrient status of most soils.
Fertiliser
use in African countries remained low and was below the need to meet
future production. Annual growth rates in fertiliser use in East Africa
was about 10% in the 1960s but had decreased to 0.7% in the 1990s. In
Southern Africa annual growth rates in fertiliser use decreased from 10%
in the 1970s to –3.4 in the 1990s. Overall growth rates in sub-Saharan
Africa remained behind the developing world since the 1960s although the
gap widens in the 1980s and 1990s. In
sub-Saharan Africa, average fertiliser use in 1990 was 8 kg nutrients per
ha arable land and land under permanent crops, as compared to the world
average of 93 kg ha–1 and 81 kg ha–1 for
developing countries. In addition most of the inorganic fertilisers in
Sub-Saharan Africa was used on plantation corps and the majority of the
smallscale farmers do not use fertilisers.
Currently, large scale and widespread inorganic fertiliser trials are no
longer conducted. Instead of advocating the use of inorganic fertilisers,
studies in the late 1980s and early 1990s focussed on new arguments to
justify the use of inorganic fertilisers. This was found when nutrient
balances were re-introduced as a research tool and widespread soil
fertility decline and nutrient mining were being reported, particularly
for sub-Saharan Africa. Not only inorganic fertilisers are being advocated
but integrated nutrient management is promoted to improve the overall
negative nutrient balance and the efficiency of nutrient use.
Decreasing
inorganic fertiliser use
Locally
it was noted that inorganic fertilisers had little or no effect due to
crop husbandry practises (poor seedbed preparation, improper seeding,
delay in sowing etc.) or because of wrong fertiliser placement, unbalanced
nutrient application, incorrect identification of nutrient limitations, or
weed and insect problems. These factors were mostly eliminated when
fertiliser trials were conducted on a research station but came to surface
when fertilisers were used by smallholders. As an overall result inorganic
fertilisers gave a poor profitability which affected the widespread use in
smallholder farming systems in many tropical regions.
Some of the fertilisers being used in tropical regions were given as aid
by European countries. This was meant to stimulate the use of fertilisers
in tropical regions and increase crop production but also meant that aid
funds were retained in Europe. Moreover European countries could maintain
their fertiliser industry which suffered from the declining rate of
fertiliser use by European farmers. The decline in inorganic fertiliser
use started in the 1980s when environmental concerns about inorganic
fertilisers were rising like the eutrophication of surface water and the
nitrate content of drinking water which is said to create health hazards
for humans under specific conditions. Inorganic fertilisers have also been
associated with the destruction of the ozone layer as nitrous oxides
resulting from denitrification can give rise to products which catalyse
ozone destruction. In other words fertilisers were regarded as
environmental damaging and as such their use was reduced.
The negative image of inorganic fertilisers in the temperate regions had
probably some indirect effects on the use of fertilisers in the tropical
regions although the environmental consequences of continued low use of
fertilisers are more devastating than those anticipated from increased
fertiliser use in the tropics. The FFHC, which was replaced in the late
1970s by FAO´s Fertiliser Programme gradually ceased in the 1990s and
currently FAO has no such programme. With a few exceptions, large scale
and widespread inorganic fertiliser trials are no longer conducted.
Instead of advocating the use of inorganic fertilisers, studies in the
late 1980s and early 1990s focussed on new arguments to justify the use of
inorganic fertilisers. This was found when nutrient balances were
re-introduced as a research tool and widespread soil fertility decline and
nutrient mining were being reported for sub-Saharan Africa. Not only
inorganic fertilisers are being advocated but integrated nutrient
management is promoted to improve the overall negative nutrient balance
and the efficiency of nutrient use.
(This
section is based on Chapter 2 from the book
"Soil fertility
decline in the tropics, with case studies on plantations".)
Publications
Hartemink,
A.E. 2003
Soil fertility decline in the tropics with case studies on
plantations. 360 pp. ISRIC-CABI, Wallingford. [with a
Foreword by Prof D.J. Greenland]. More info
here
Kauffman, J.H. & A.E.
Hartemink 2003 Soil potential and constraints
for increased agricultural production in the low yield areas of West
Africa. In: People matter: food security and soils. R. Lahmar, M. Held and
L. Montanarella (Eds). Torba, Montpellier pp. 32-43.
Offprint
Bouma, J. & A.E. Hartemink 2002
Soil science and society in the Dutch
context. Netherlands Journal of Agricultural Science 50: 133-140.
Offprint
Hartemink,
A.E. 2002 Soil science in tropical and temperate regions – Some
differences and similarities. Advances in Agronomy 77: 269-292.
Offprint
Hartemink, A.E. & R.M.
Bourke 2000 Nutrient deficiencies of agricultural
crops in Papua New Guinea. Outlook on Agriculture 29: 97-108.
PDF
Hartemink, A.E., M.
Johnston, J.N. O’Sullivan. S.
Poloma 2000 Nitrogen Use
Efficiency of taro and sweet potato in the humid lowlands of Papua New
Guinea. Agriculture, Ecosystems and Environment 79: 271-280.
PDF
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