Home
Various activities
Research
     Bioinvasion
       Digital soil map
     Fallows
     Fertilisers
     History
     Plantations
     Publishing
     Root crops
     Soil fertility 
     Soil museum
     World food
Teaching
Publications
Contact
 
   
   
 



 
Inorganic fertilisers

 

 

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

 

     

www.alfredhartemink.nl