# FERTILIZER INFORMATION SHEET (Draft for review and comment -- June 8, 2004)

**Background** - Low soil fertility is a problem throughout most of
Sub-Saharan Africa (SSA). Moreover, the drastic reduction in fallow
periods and the almost continuous cropping without soil fertility
restoration has depleted the nutrient base of most soils. By the
mid-late 1990s, all SSA countries were demonstrating a negative annual
nutrient balance **^1^**. Countries that have the highest nutrient loss
rates are the ones where fertilizer use is low and soil erosion is high.
These areas include the East African highlands and a number of countries
in West Africa.

Low soil fertility is also a driving force behind the conversion of
natural areas for agricultural extension. It is generally accepted that
agricultural intensification is the only viable means to conserve key
natural areas while increasing food security for the continents growing
population and generating economic growth through improved agricultural
productivity. Land degradation undermines the ability of countries to
move in this direction, and the loss of soil nutrients is the most
important contributing factor to the land degradation process. The use
of inorganic fertilizers is a critical part of the strategy to stop land
degradation, restore soil fertility and better manage the soil resources
that are fundamental for sustainable agricultural and economic
development.

**The Importance of Water Management** **to Nutrient Uptake** - Proper
water management is important for maximizing crop use of nutrients.
About 97% of crop nutrient uptake is from soil solution (water-soluble
nutrients), which makes water by far the most important nutrient or
fertilizer delivery medium. This also means that, for the most part,
nutrient mobility is directly linked to water movement. In sandy soils,
nutrients move more quickly through the root zone and soil profile than
in other soil types, and excessive water application (or heavy rainfall)
can lead to nutrient loss through leaching. Run-off is most serious on
loamy-sands or sandy loams that often have a strong surface crust
formation. In heavier soils (clays), if nutrients are not adequately
incorporated into the soil, the chances for surface runoff in the event
of heavy rains or over-irrigation are increased. Sound water management
is especially important in rainfed conditions (common throughout SSA).
Overall, good water management leads to a more efficient use of
fertilizers and increased nutrient uptake and vice versa.

### General trends in Africa:

-   Farmers who have taken measures to conserve moisture or increase
    soil organic matter are more likely to use inorganic fertilizer.
    When farmers in some areas have capital, they often invest first in
    increasing moisture retention and/or increasing soil organic matter
    and secondly in inorganic fertilizer.

-   Farmers increase their use of fertilizer when investing more money
    in fertilizer is seen to be the best available option. This increase
    may result from changes in any of the following: fertilizer price,
    crop price, fertilizer availability, water availability, seed
    availability, knowledge about fertilizer use, or cropping pattern.

-   In West Africa, integrated soil fertility management is
    progressively adopted. It concerns the combined use of soil
    amendments and inorganic fertilizer, leading in time to improved
    soil fertility and increased fertilizer use efficiency and
    profitability. The nutrient losses to the environment are
    decreasing.

-   Given past and current use rates, USAID's fertilizer-related
    activities in Africa are unlikely to cause environmental
    problems**.**

### Application guidelines:

-   Before applying fertilizers, obtain an assessment of soil conditions
    (fertility).

-   Indiscriminate use of chemical fertilizers should be avoided.

-   Different kinds of fertilizers are required in order to maintain a
    given level of soil fertility. This depends on site-specific
    factors, including the soil type, the nutrient requirement of the
    crop and the various sources of available nutrients. Nitrogen and
    Phosphorous are the most important nutrients lacking in SSA soils.

-   Fertilizer application has to be considered in the context of the
    overall farming system. This includes the use of organic manure and
    residues, soil cultivation and crop rotation and water harvesting.
    Collectively, these factors influence the efficiency of nutrient
    use.

-   When fertilizers are used, it is very important to apply the correct
    amount for the given situation. The challenge to the farmer is to
    match as closely as possible the input of nutrients to the nutrient
    uptake of the crop, thereby minimizing losses. Over fertilization is
    both costly (wasteful) and potentially harmful to the environment.
    To apply the correct amount, the farmer has define his production
    goal.

### Potential negative environmental effects of fertilizers:

Excessive application of nutrients over time can cause pollution. Such
losses may occur when nutrients run off the land caused by heavy
rainfall, are leached through the soil, beyond the root zone, eventually
reaching the groundwater, or escape into the atmosphere as volatile
gases.

Aspects of environmental impact can be illustrated as follows:

![](media/image1.png){width="4.586805555555555in"
height="1.3194444444444444in"}

(Taken from Incitec Fertilizers)

**Nitrogen fertilizers**: Inorganic nitrogen fertilizers are readily
converted by soil organisms to nitrate in the soil. The nitrogen in soil
organic matter and organic fertilizers becomes available more slowly.
Nitrates may be readily leached if not used by crops or other
vegetation. Leaching is particularly likely in sandy soils following
heavy rainfall. Leached nitrates may contaminate underground water. This
is of concern if the water is to be used for human or livestock
consumption, as high concentrations of nitrate may affect health.

Nitrogen fertilizers can also accelerate the natural process of soil
acidification. Some fertilizers (e.g. anhydrous ammonia and urea) may
initially raise the soil pH at the site of application but in the long
term acidify the soils. This occurs when ammonium is converted to
nitrate. Acid produced in the nitrification process is used if the
nitrate is taken up by plants or soil organisms, but if the nitrate is
leached beyond the root zone, acidification occurs. Soil acidification
reduces the availability of the trace element molybdenum, fosters the
development of aluminum, iron and manganese toxicity and increases
nodulation failure in legumes. Lime may be required where acidity is a
problem (obtained from naturally occurring calcium carbonate) or the use
of acid tolerant plant species can be considered. An illustrative list
of crops with acid tolerant varieties include: rice, cassava, mango,
cashew, citrus, pineapple and cowpeas.\
\
**Phosphorus fertilizers:** Excess amounts of phosphorus have been
associated with algal blooms and the eutrophication of lakes and
waterways. In most waters phosphorous functions as a growth-limiting
factor because it is usually present in very low concentrations. Algae
only require small amounts of phosphorous to live. Excessive phosphorus
over-stimulates the growth of algae, which could deplete the water of
the dissolved oxygen that is vital to other aquatic life. Phosphorus is
relatively immobile in the soil, so conservation and cultural practices
which reduce soil erosion can significantly reduce phosphorus inputs
into water bodies and the water table.

Phosphorus fertilizers contain various impurities from the phosphate
rock and acid used in manufacturing the fertilizer. Increases in cadmium
is the greatest concern as its compounds are toxic to human beings.
Cadmium increases are most noticeable in certain crops e.g. potatoes and
leafy vegetables (lettuce and spinach) and in the organs (kidneys and
liver) of animals. Almost all phosphate fertilizers contain traces of
cadmium, and the concentration of cadmium varies considerably from
source to source. At this time, there are efforts underway in West
Africa to develop viable processes to remove cadmium from phosphate
rock. Exports of rock phosphate represented a vital source of revenue
for a number of developing countries in Africa.

**Effects on Soil Biology**: Good soil consists of 93% mineral and 7%
bio-organic substances. The bio-organic parts are humus (85%), roots
(10%) and soil organisms (5%). Most of the soil organisms are
decomposers (bacteria and fungi), which are responsible for nutrient
retention in soil. In order for nutrients to become available they must
be mineralized by the interaction of decomposers and organisms that feed
on the decomposers (protozoa, nematodes, micorarthropods and
earthworms). Plant growth is dependent on microbial nutrient
immobilization. When the number of decomposers declines in soils, more
nutrients are lost into the ground and surface water. Heavy treatments
of chemical fertilizers can kill decomposers and other soil organisms,
which will lead to a reduction in nutrient retention and possible
surface and ground water contamination.

### A summary of best management practices for soil fertility and health:

-   Integrated Soil Fertility Management (ISFM) -- the use of both
    organic and inorganic sources of nutrients rather than either alone;

-   The use of legume cover crops (plus phosphorous) and green manures
    by fallow rotation or intercropping;

-   Agroforestry practices -- in addition to soil conservation and
    production benefits, agroforestry transfers/cycles nutrients from
    within the soil profile (deeper levels to surface);

-   The use of conservation tillage rather than deep plowing (although
    conservation tillage can be harmful for production systems in
    certain regions **^2^)**;

-   Use farm site manures and household wastes, with or without
    composting;

-   Choose crops and associated plants that have high nutrient use
    efficiency.

### Fertilizers and US Government regulations (22 CFR 216):

Fertilizers are frequently lumped together with pesticides under the
generic heading, "agro or agrichemicals." From an environmental
compliance perspective (22 CFR 216), as well as from a field-level
implementation point of view, this is unfortunate because it implies
that fertilizers require the same level of scrutiny reserved for
pesticides. Whereas pesticides are subject to clearly defined procedures
and an approval process, the same is not true for fertilizers. As with
any technology, however, it is recommended that fertilizers be
thoughtfully employed within the context of the prevailing biophysical
and socio-economic conditions as well as the desired outcomes. This fact
sheet was developed to assist in that regard.

Notes:

1.  Henao, J. and Baanante, C. 1999. Estimating rates of nutrient
    depletion in soils of agricultural lands of Africa. Technical
    Bulletin. IFDC -- T 48. IFDC, Muscle Shoals, Alabama. 76p.

2.  Hoogmoed, W. 1999. Tillage for soil and water conservation in the
    semi-arid tropics. Phd thesis, Wageningen University, Holland.

### Additional Reading: 

Wallace, M.B. 1997. Fertilizer Use and Environmental Impacts \--
Positive and Negative:

A Review with Emphasis Upon Inorganic Fertilizers in Africa. Winrock.

Kelly, V.A., Crawford, E.W., Howard, J.A., Jayne, T., Staatz, J. and
Weber, M.T. 1999. Towards a

Strategy for improving agricultural inputs markets in Africa. Policy
Synthesis, no. 43 USAID Bureau of Agriculture and Food Security and the
Office of Sustainable Development.

Jayne, T.S., Kelly, V.A., and Crawford, E. 2003. Fertilizer consumption
trends in Sub-Saharan Africa.

Policy Synthesis, nos. 69. USAID, Bureau of Agriculture and Food
Security and the Office of Sustainable Development.

Kelly, V.A., Crawford, E. and Jayne, T.S. 2003. Agricultural input use
and market development in Africa: Recent perspectives and insights.
Policy Synthesis, no. 70. USAID, Bureau of Agriculture and Food Security
and the Office of Sustainable Development.

The Soil Foodweb: Its importance in ecosystem health.
[www.rain.org/\~sals/ingham.html](http://www.rain.org/~sals/ingham.html)

Swift, M. Soil Biodiversity Principles, Tropical soil and biology
fertility programme.
[www.unep.org/bpsp/Agrobiodiversity/agrobiodiversity%20thematic/soilbiodiv.pdf](http://www.unep.org/bpsp/Agrobiodiversity/agrobiodiversity thematic/soilbiodiv.pdf).

European Fertilizer Manufacturers Association. Agriculture, fertilizers
and the environment.
[www.efma.org/Publications/EUBook/Section13.asp](http://www.efma.org/Publications/EUBook/Section13.asp).

The PotashCorp. Fertile Minds Program.
<http://www.fertile-minds.org/support/cdrom_available.php>.

Incitec Fertilizers.
<http://www.incitecfertilizers.com.au/environmental_facts.cfm>.