Agriculture Reference
In-Depth Information
Table 2.4.
Distribution of major soils in the tropics (after Sanchez, 1976; Sanchez
and Salinas, 1981).
Humid
tropics
a
(%)
Dry and
arid
(%)
Seasonal
(%)
Tropics
(%)
Highly weathered, leached, red or yellow
soils - (oxisols, ultisols, al
fi
sols)
36
61
2
51
Dry sands and shallow soils - (entisol-
psamments and lithic group)
10
33
58
17
Light-coloured, base-rich soils - (aridisols
and aridic groups)
0
15
85
14
Alluvial soils - (inceptisol-aquepts,
entisol-
fl
uvents)
40
52
8
8
Dark-coloured, base-rich soils - (vertisols,
mollisols)
8
60
32
6
Moderately weathered and leached soils -
(inceptisol-andepts and tropepts)
7
59
34
4
% of tropics 24 49 27 100
a
Classi
fi
ed on number of rainy months: humid tropics, 9.5-12 months; seasonal, 4.5-9.5
months; dry and arid, 0-4.5 months.
deserts (14%) can be very productive with irrigation. Nitrogen defi ciency
and sometimes salinity can be problems. The 17% covered by dry sands
and shallow soils are greatly limited in agricultural productivity. The most
important aspect is the development of management strategies for the dif erent
tropical soils, taking into consideration their unique properties. Management
practices developed in temperate regions may not be directly transferrable.
Soil physical characteristics are of primary concern for tropical fruit
production, with soil nutrients being secondary because they can normally be
readily corrected. Soil texture and structure, soil water storage and drainage
are crucial. Defi ciencies in these characteristics are major constraints to
production because they are dii cult and expensive to correct. Under natural
conditions, most soils considered for fruit crops in the tropics have a good
topsoil structure. This includes the highly weathered oxisols and ultisols (Table
2.5). Loss of organic matter may lead to loss of structure and crusting of these
soils after heavy rains. Some soils, however, do not favour root development
due to a dense subsoil layer that needs to be broken during soil preparation to
avoid shallow root systems. Heavy machinery may also cause the formation
of a compact subsurface layer in medium-textured oxisols with low iron and
in fi ne-textured oxisols. Low calcium and phosphorus and high aluminium
contents in the subsoils can also restrict root growth.
Tropical fruit crops have shown a wide range of soil adaptability and
have been observed to grow and produce well in a wide variety of soil types,
