Constraints in Irrigated Lowland Rice Cultivation as Affected by the Harmattan in Guinean Savanna Zone of Central Côte d'Ivoire

Lowland rice accounts for about 36% of the total rice area in Côte d'Ivoire and contributes over 20% of total paddy production. Lowland rice cultivation under flooded or irrigated conditions has a potential average yield of 6-8 t/ha, with the possibility of two cropping cycles per year. Despite the availability of water in these lowlands, which could allow three cropping cycles per year, farmers are limited to two cycles due to the impact of the Harmattan, which occurs in the last trimester of the year and severely affects yields. Harmattan is characterised by low temperatures associated with dusty winds during two-thirds of the dry season in the bimodal rainfall area of the Guinea savannah in West Africa. This particular climate adversely affects rice production even in irrigable lowland perimeters, allowing only one cycle of rice production instead of two or three. In order to improve rice production in this agroclimate, it is necessary to diagnose the constraints. Two agronomic trials were conducted in the irrigable valley of M'bé II, in a Guinea savannah zone of central Côte d'Ivoire. The first trial was an omission trial (Fc-N, Fc-P, Fc-K, Fc-Ca, Fc-Mg and Fc-Zn) with a complete fertiliser (Fc) consisting of 30 kg N ha-1, 60 kg P ha-1, 50 kg K ha-1, 50 kg Ca ha-1, 50 kg Mg ha-1 and 10 kg Zn ha-1. The control was no fertiliser treatment. All treatments consisted of NPK applied at the same rates and Ca (0, 50, 100 and 150 kg ha-1), Mg (0, 50, 100 and 150 kg ha-1) and Zn (0, 10, 20 and 30 kg ha-1) added in the respective treatments. The application of N, K and Mg can increase the yield of irrigated rice in the Harmattan period. Further improvement can be observed by combining 90 kg Ca ha-1 with NPK.