Baanante, Carlos A.

Henao, Julio

English

Research Papers in Economics

NUTRIENT DEPLETION IN THE AGRICULTURAL 
SOILS OF AFRICA 
Julio Henao and Carlos Baanante 
2020 BRIEF 62  A 2020 Vision for Food, Agriculture, and the Environment  OCTOBER 1999 
About two-thirds  of Africans  depend  on  agriculture for their 
livelihoods.  The  fate  of agricultural production, therefore,  di-
rectly affects economic growth, social improvement, and trade 
in Africa. As the region's population continues to grow rapidly, 
outpacing the growth rate in other regions of the world, its agri-
culturalland is becoming increasingly degraded. Farmers are 
intensifying land use to meet food needs without proper man-
agement practices and external inputs. The resulting depletion 
of nutrients from soils has caused crop production to stagnate 
or decline in many African countries. In some cases, notably in 
the East African highlands, the rate of depletion is so high that 
even drastic measures, such as doubling the application offer-
tilizer  or  manure  or  halving  erosion  losses,  would  not  be 
enough to offset nutrient deficits. Unless African governments, 
supported  by  the  international  community,  take  the  lead  in 
confronting  the  problems  of nutrient depletion,  deteriorating 
agricultural productivity will seriously undermine the founda-
tions of sustainable economic growth in Africa. 
THE EXTENT OF NUTRIENT DEPLETION 
All  African countries,  except Mauritius,  Reunion,  and  Libya, 
show negative nutrient balances every year (see Figure 1). In 
the semiarid, arid, and Sudano-Sahel ian areas that are more 
densely populated,  soils lose 60-100 kilograms of nitrogen, 
phosphorus, and potassium (NPK) per hectare each year. The 
soils of these areas are shallow, highly weathered, and subject 
to intensive cultivation but with low levels of fertilizer applica-
tion. Limited water availability and intensified land use due to 
increasing population size have restricted crop diversification 
and  the  adoption  of proper  management  practices.  Short 
growing seasons contribute to additional pressure on the land. 
In other important agricultural areas, such as those located 
in the subhumid and humid regions and in the savannas and 
forest  areas,  nutrient  losses  vary  greatly.  Rates  of nutrient 
depletion range from moderate (30 to 60 kilograms of NPK per 
hectare per year) in the humid forests and wetlands in south-
ern Central  Africa,  to  high  (above 60  kilograms) in  the  East 
African highlands. 
In 1993-95 the difference between nutrient inputs and nutri-
ent losses in the continent ranged from -14 kilograms of NPK 
per  hectare  per year  in  South  Africa  to  -136  kilograms  in 
Rwanda. Burundi and Malawi also experienced rates of  nutrient 
depletion  above  100  kilograms of NPK per hectare per year. 
About 86 percent of African countries show annual nutrient defi-
cits  greater than  30  kilograms  of NPK per heclare per year. 
More  countries  fall  into  the  high  depletion  range  than  the 
medium range. Nutrient imbalances are highest where fertilizer 
use is particularly low and nutrient loss, mainly from soil erosion, 
Figure 1-Average annual nutrient depletion (NPK) in 
Africa, 1993-95 
Kilograms of NPKlhectare 
D  More than 60 
D  30 - 60 
D  Less than 30 
JJ'~~,:  No depletion  • 
No data 
is high. The low gains in nutrients, inherently low mineral stocks 
in these soils,  and  the harsh climate of the interior plains and 
plateaus aggravate the consequences of nutrient depletion. 
The estimated net annual losses of nutrients vary consid-
erably by  subregion:  384,800  metric tons for  North  Africa, 
110,900 metric tons for South Africa, and 7,629,900 metric 
tons for Sub-Saharan Africa.  This represents a total loss of 
US$1.5 billion per year in  terms of the cost of nutrients as 
fertilizers. Forfeited yields cause additional financial losses. 
Most  crop  yields  in  Africa  did  not  change  substantially 
between  1981  and  1995,  remaining  close  to  the  average 
obtained by smallholders with rainfed land and moderate to 
low soil fertility. 
More  nitrogen  and  potassium  than  phosphorus  get  de-
pleted from African soils. Nitrogen and potassium losses pri-
marily arise from leaching and  soil erosion. These soil prob-
lems  result  mainly  from  continuous  cropping  of  cereals 
without rotation with legumes, inappropriate soil conservation 
praclices, and  inadequate amounts of fertilizer use. Guinea 
Bissau and  Nigeria experience the highest annual losses of 
nitrogen and potassium in West Africa. Nitrogen loss in East 
Africa is highest in  Burundi,  Ethiopia, Malawi,  Rwanda, and 
Uganda, and phosphorus loss is highest in  Burundi, Malawi, 
and Rwanda. 
Losses of  potassium are associated with severe erosion. The 
highest rates  of potassium  depletion occur in  Guinea Bissau 
INTERNATIONAL FOOD POLICY RESEARCH INSTITUTE  0  2033 K STREET, NW,  0  WASHINGTON, D.C. 20006-1002 U.S.A  . 
. i.I!.  PHONE: 1-202-862-5600  0  FAX: 1-202-467-4439  0  E-MAIL:  ifpri@cgiar.org  0  WEB: www.ifpri.org 
~~  IFPRI is part of a global agricultural research network, the Consultative Group on International' Agricultural Research (CGIAR). and  Nigeria  in  West  Africa,  and  Burundi,  Kenya,  Malawi, 
Rwanda, Swaziland, and Uganda in East and Southern Africa. 
NUTRIENT REQUIREMENTS AND SOIL 
MANAGEMENT PRACTICES 
Nutrient gains  in  African  soils come  about  mainly through 
mineral fertilizer application, nutrient deposition, and nitrogen 
fixation. The negative nutrient balances clearly indicate that 
not enough nutrients are being  applied in  most areas.  The 
current (1993-95) annual use of nutrients in Africa averages 
about 10 kilograms of NPK per hectare. Fertilizer use ranges 
from  nearly 234 kilograms per hectare in  Egypt to  46 kilo-
grams in Kenya to less than 10 kilograms in most countries in 
Sub-Saharan Africa.  North Africa,  with  about 20  percent of 
the continent's land area, accounts for 41  percent of the fertil-
izer consumption. 
Fertilizer tends to  be  used  mostly on  cash  and  plantation 
crops because of the high profitability of fertilizers in the pro-
duction of export crops. Food crops get less fertilizer because 
of unfavorable  crop/fertilizer  price  ratios  and  financial  con-
straints faced by farmers. 
To maintain current average levels of crop production with-
out depleting soil  nutrients, Africa will  require approximately 
11.7 million metric tons of NPK each year, roughly three times 
more than it currently uses (3.6 million metric tons) (see Fig-
ure 2). Sub-Saharan Africa will need by far the largest propor-
tion of this amount, 76  percent,  because its current average 
level of fertilizer use is so low. Total nutrient requirements per 
hectare  per  year  in  this  subregion  range  from  Botswana's 
24.5  NPK  (a  figure  350  percent  above  current  usage)  to 
Reunion's 437.3 NPK (about 20 NPK per hectare less than the 
country consumes). Burkina Faso would have to  increase its 
NPK consumption more than  11  times to  maintain crop pro-
duction levels without depleting nutrients and Swaziland would 
have to double its  consumption.  Estimated  average use  for 
Africa  as  a whole would  have to  increase  about 4 times to 
meet nutrient needs at the current level of production. Gener-
ally  more  nitrogen  is  required  than  potassium,  and  more 
potassium than phosphorus. 
Although increasing the use of mineral fertilizer may be the 
centerpiece of the strategy to balance nutrient depletion and 
improve soil  productivity in  Africa,  it  should  not  be taken  to 
mean that fertilizer levels should be increased beyond  basic 
requirements.  Indeed,  surpassing  recommended  levels  for 
less-responsive varieties and in poorly managed cropping sys-
tems can lead to high nutrient losses and low yields. Moreover, 
to  achieve  intended  goals,  fertilizer  use  must  be  combined 
with a broad  spectrum of complementary practices, such as 
soil  conservation,  recycling of crop residues,  livestock man-
agement, and use of organic fertilizers. Such practices could 
reduce the mineral fertilizer required to maintain current aver-
age yields by as much as 44 percent. 
Figure 2-Annual requirements for maintaining 
current yields without depleting nutrients, 
1993-95 
Kilograms of NPKlhectare 
D  More than 80 
IillTI  41 - 80 
D  20-40 
•  Nodata 
IMPLICATIONS FOR POLICY 
If nutrient depletion and land degradation continue at current 
rates, one has to wonder how farmers in African countries will 
be  able to grow enough food for ever-larger populations in 
the next century. To avoid  possible crises, national govern-
ments  and  donors  should  address  the  threat  of  nutrient 
depletion  and  land  degradation  through  policies  and  pro-
grams that promote increased productivity of land resources 
and  conservation  of the  resource  base.  Significant  policy 
changes  will  be  required  to  establish  an  environment that 
makes agricultural  inputs easily available, that encourages 
farmers to use these inputs more efficiently, and that helps 
improve local extension services and farmer support. Struc-
tural adjustments, market development, trade and price poli-
cies, credit systems, infrastructure improvement, and institu-
tional support services should be reevaluated and assessed 
for their impact on the resource base and the sustainable ex-
pansion of agricultural production and productivity. 
Many countries and  regions  need  to  integrate  natural  re-
source management with economic and sector policies. More 
economic and  environmental impact analyses at the country 
level  are  needed  to  help  set  priorities  for  agricultural  land 
issues, to assess the costs and  benefits of  policy decisions, 
and to expedite identification of  the type of investments that will 
be required to prevent land degradation and increase produc-
tion.  Prevention  of nutrient mining  through  sound  economic 
policies,  research,  information dissemination,  and  human re-
source development should be actively promoted in Africa. 
For more information see the Jull report by Julio Henao and Carlos Baanante, Estimating Rates of Nutrient Depletion in Soils of Agricultural Lands of  Africa 
(Muscle Shoals, Alabama,  USA:  International Fertilizer Development Center,  1999). 
Julio Henao is senior scientist-biometrician at the  International Fertilizer Development Center (lFDC),  a-mail: Jhenao@ifdc.org.  Carlos Baanante is 
.  director of  research and development at IFOC, e-mail: cbaanante@ifdc.org. 
"A 2020 Vision for Food, Agriculture, and the Environment" is an initiative of the International Food Policy Re-
search Institute (IFPRI) to develop a shared vision and a consensus for action on how to meet future world 
food needs while reducing poverty and protecting the environment. Through the 2020 Vision initiative, IFPRI 
is bringing together divergent schools of thought on these issues, generating research, and identifying recom-
mendations. The 2020 Briefs present information on various aspects of the issues. 
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Nutrient depletion in the agricultural soils of Africa:

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Nutrient depletion in the agricultural soils of Africa:

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