Bananas and Food Security - Bioversity International

640 Les productions bananières / Bananas and food security – Session 4
cultivation systems, semi-intensive rainfed systems, intensive rainfed systems, irrigated
and flooded systems, mixed annual/perennial systems. It is rather clear that both banana
and plantain are cropped in all these various systems. The huge diversity of banana
cropping systems is due to a large variation in ecological conditions (soil, climate) as well
as in technical inputs and socio-economic environments.
Intensive dessert banana cropping systems for export and local market have been
extensively described and studied in such a way that precise recommendations can be
given with respect to farm management and culturing techniques (Robinson 1995).
However, high-input cropping systems may result in rapid environmental degradation
and in decreasing cycle-to-cycle crop yields. In this respect, soil fertility research is
clearly needed to answer the demand for sustainable agricultural and environmental
conservative production. Such a need is also felt in traditional cropping systems, because
soil fertility depletion is a major cause of crop yield decline (Chataigner 1988, Davies
1995, Temple 1995). This is particularly needed because bananas use considerable
amounts of water and mineral nutrients for growth and fruit production (Robinson 1995,
Lahav 1995) though they have a weak root system (Swennen 1984, Price 1995b, Delvaux
1995). Indeed, the banana root length density (RLD) is = 0.12-0.13 cm/cm -1 against RLD
values for cereal crops ˜ 0.5 cm/cm -1 (Brisson et al. 1998); the roots are usually confined
in the topsoil (25-35 first cm) and do not easily extent downwards, except in soils with
particularly high porosity (Delvaux 1995). Table 1 illustrates the quantities of water and
mineral nutrients immobilised by one high yielding banana plant during one cropping
cycle. Noteworthy is the high consumption of water, nitrogen and particularly potassium.
Only a part of the immobilised nutrients is exported by bunch harvesting: the mineral
masses immobilised to produce 1 tonne of fruits would amount to (kg) 4.3 N and 15.8 K,
i.e. 1.63 N and 4.82 K exported by the bunch.
Surprisingly and though large possibilities exist to improve crop performance
(Chataigner 1988), very little research has been devoted to the quantification of nutrient
Table 1. Average water and mineral immobilization by one Grande Naine banana
plant for a crop yield level around 60-65 t/ha (harvesting stage, roots excluded)
(adapted from Lahav 1995).
whole plant fruit
Fresh weight (kg) 175 63
Water mass (kg)
Mineral nutrients (g):
137 31
N 175 63
K 647 185
P 18 7.5
Ca 96 4.5
Mg 38 10
S 17 7.5
Mn 9 0.6
Fe 5 0.7