Abstract

                                An attempt was made to identify the exact influences of the unfavorable characteristics of laterite soil on the productivity process using a medicinal rice type, Njavara. Three distinct phases could be identified in the nutrient uptake pattern, corresponding to the development of the plant: an accumulation phase, a dilution phase and finally, a diversion phase. The diversion phase is characterized by a decrease in dry matter accumulation due Tiller decline, which can be related to stress in the plant. Very high content of micronutrients especially of iron and manganese, in the plant could lead to inhibited metabolism and was probably the reason for low realized yields. Death of late formed tillers could thus be a protective mechanism of the plant to shed the unfavourably high levels of iron and manganese which limit growth and yield. Increased nitrogen application failing to increase yield is an indication of degraded soils, where absorption of nutrients takes place, but their transformation into yield is inhibited. Amelioration of these harmful effects is the sole way of increasing productivity

Key words : Njavara, laterite soils, tiller decline, stress influence