Response of lowland rice to phosphate amendments in three acidics agroecological zones of Côte d'Ivoire: Man-Gagnoa-Bouaké

The need to achieve self-sufficiency in rice led producers to overexploit soils and to use excessively chemical fertilizers, which deplete soils and make phosphorus unavailable to crops. As an alternative, eight phosphate amendements made from phosphate rocks from Morocco (MPR), Triple Superphosphate (TSP) and NPK (T0a (0%MPR + 0%TSP without NPK); T0 (0%MPR + 0%TSP+ NPK); T1 (100%MPR + 0%TSP+ NPK); T2 (90%MPR + 10%TSP+ NPK); T3 (80%MPR + 20%TSP+ NPK); T4 (40%MPR + 60%TSP+ NPK); T5 (20%MPR + 80% TSP + NPK); T6 (0%MPR + 100%TSP+ NPK) were applied to the field and their agronomic efficiencies were evaluated in Man (very acidic soil). Gagnoa (moderately acidic soil) and Bouaké (weakly acidic soil). After three cultivation cycles, results designate Man and Gagnoa as more productive zones with respectively 5.04 t ha-1 and 4.36 t ha-1 grain yield (GY), comparatively to Bouaké (3.74 t ha-1). Likewise, straw yields (SY) are 9.68 t ha-1 at Man and 6.06 t ha-1 at Gagnoa, comparatively to Bouaké (5.85 t ha-1). Treatments T3 and T4 were more productive in all zones with respectively GY of 7.50 t ha-1 and 6.50 t ha-1 in Man, 5.54 t ha-1 and 5.91 t ha- 1 in Gagnoa and 5.55 t ha-1 and 4.84 t ha-1 in Bouaké. This disparity is due to the chemical properties of the soils. In Man, Gagnoa and Bouaké, the combination 80% MPR + 20% TSP and 40% MPR + 60% TSP seem to improve better the yield of lowland rice.