Mining of Nutrients in African Soils Due to Agricultural Intensification - Principles of Sustainable Soil Management in Agroecosystems - page 409

NPK(t) net trade in 1997 and 2020 by region

ROW
China
SE Asia
S Asia
WA NA
Sub-Saharan Africa

Latin America
Former USSR
E Europe
Other developed
Australia

-1997
-2020

NPK

Japan

EC15

USA

-5,000,000 -4,000,000 -3,000,000
Exporter

-2,000,000 -1,000,000 0 1,000,000 2,000,000 3,000,000

Importer

FIGURE 15.4 Nutrient flows in net trade of agricultural commodities in 1997 and projected
to 2020. (From Craswell, E.T. et al., Nutrient flows in agricultural production and interna-
tional trade: Ecological and policy issues, ZEF Discussion Paper on Development Policy
No. 78, Center for Development Research, University of Bonn, Bonn, 2003.)

increase to 0.662 Tg of NPK in 2020. This positive side of the net trade balance is
much less than that in less populous, net food importing, regions such as West Asia
and North Africa, reflecting the subsistent nature and self-sufficiency of many coun-
tries in SSA. It is also closely associated with differences in the availability of water
between the regions and the need for virtual water trade (Grote et al. 2007). At first
sight, the positive nutrient stream due to food imports to SSA may appear to contra-
dict concerns about soil nutrient mining in rural areas due to low rates of fertilizer
inputs. However, the data presented are averages across and within countries. If, as
appears likely, the nutrients imported in food are consumed and end up as wastes in
the major cities, distant rural lands will not benefit. The imported nutrients represent
a useful resource, considering that the 1997 level represents 26% of the 1.102 Tg of
NPK fertilizer used in that year. As mentioned above, an issue in SSA is that the fer-
tilizer data used by Grote et al. (2005) include nutrients applied to plantation crops,
whereas the NPK net trade data exclude plantation and industrial crops. Vlek (1993)
estimated that in 1987, the net export from Africa of N, P 2 O 5 , and K 2 O in agricultural
commodities, mainly cotton ( Gossypium spp.), tobacco ( Nicotiana tobacum ), sugar
( Saccharum officinarum), ), coffee ( Coffea spp.), cocoa ( Theobroma cacao ), and tea
( Camellia sinensis ), was 0.296 Tg.

15.2.3 n utrient B AlAnceS At n AtionAl S cAle
Several major studies have utilized NUTMON or similar formulae to calculate
nutrient balances for arable land on an average basis for different African coun-
tries. Table 15.4 shows a comparison of the data on nutrient mining from two such