Iron toxicity is a widespread nutrient disorder of lowland rice in West Afr
ica. Soluble iron present in the soil solution under waterlogged conditions
is absorbed by roots and accumulates in leaves. It causes poor growth and
tillering and severe yield reductions, associated with leaf discoloration.
Field experiments were conducted during 1994-1996 at an iron-toxic lowland
site at Korhogo (Ivory Coast) to study the interactions between iron toxici
ty and the addition of various plant nutrients. Nine nutrient element treat
ments (combinations of N, P, K and Zn, including no fertilizer) were tested
on one iron-susceptible (Bouake 189) and one iron-tolerant (CK 4) cultivar
. The application of P, K and Zn with N reduced iron toxicity symptoms and
increased yield in both cultivars. Strong correlations were observed betwee
n grain yield and scored leaf iron toxicity symptoms across seasons and tre
atments. The iron-tolerant rice cultivar absorbed less iron or transported
less from roots to leaves, indicating the presence of a physiological avoid
ance mechanism. At any given concentration of iron in the leaves, net phots
ynthetic rates were lower in the susceptible than in the tolerant cultivar.
The iron-tolerant cultivar owed its superior performance under iron-toxic
conditions partly to avoidance (less iron accumulation in leaves) and toler
ance (superior photosynthetic potential in the presence of absorbed iron in
the leaves). Data indicated that these mechanisms can be further enhanced
through the application of P, K and Zn.