Diagnostic of mineral deficiencies and interactions in upland rice yield declining on foot slope soil in a humid forest zone

Abstract Haphazardly fertilization can impaired rice production inducing yield declining in continuous cropping even with high input management. To sustain upland rice production on foot slope ferralsol in a humid forest zone of West Africa, soil deficient nutrients were identified in omission trial concerning N, P, K, Ca, Mg and Zn –fertilizers in Côte d'Ivoire from 2003 to 2005. The relationship between rice grain yield and nutrient contents in soil and above ground organs were also determined. Significant (P = 0.05) yield depressions were observed for P and K exclusion treatments as deficient nutrients in the first (P) and second (PK) years. Chaminade index revealed also secondary soil deficiency for Mg and N in the subsequent year with a decreasing trend from 2003 to 2005 [N (85%, 104%, 78%), P (63%, 51%, 56%), K (95%, 44%, 62%) and Mg (87%, 85%, 64%)] likely to grain yield declining. Antagonistic relationships in rice mineral nutrition, soil leaching and acidification as well as increasing of Mn availability and soil nutrient deficiencies were main factors of yield declining. These processes were discussed to be depending on the initial soil fertility level that was somewhat differing in savanna ecology. Application of P, PK and PKNMg fertilizers were recommended for three years cropping respectively. Practice of minimum tillage and maintaining high ratio of Ca: Mg was suggested for reinforcing the yield stabilization.