Effects of rock phosphate and PK mineral fertilizer on soil fertility and cocoa production in south-central Côte d'Ivoire

Côte d'Ivoire is the world's leading cocoa producer, but sustainable cocoa production is threatened by, among other things, the country's dwindling forest reserves and declining soil nutrients, mainly phosphorus. To remedy the decline in soil fertility, a study of a mineral amendment was carried out in south-central Côte d'Ivoire to ensure the sustainability of cocoa production. Specifically, the aim was to evaluate the effects of rock phosphate (RP) and PK mineral fertilizer on soil fertility and cocoa production at Divo, over three years of trials. The experimental set-up was a Fisher block design, with 4 replications for 5 treatments. The results showed that, in terms of soil fertility, treatments receiving rock phosphate generally had good assimilable phosphorus content (≥ 11.5 Cmolkg-1), a Ca/Mg ratio of between 1 and 1.5, Mg/K≥3, (Ca+Mg)/K of between 12 and 40 and Ca/SBE x100 ≥ 68%. These ratios reflect not only good cocoa-growing soil, but also a good balance between Ca and the sum of exchangeable bases (SBE) and between K and the sum of Ca and Mg. On the other hand, all treatments had potassium deficiencies with (K/S) x100 < 8%. As for yield, treatments T1 (100%RP + 100% NPK 0-23-19) with 2953.44 Kgha-1, T2 (90%RP + 100% NPK 0-23-19) with 2962.95 Kgha-1 and T3 (80% RP + 100% NPK 0-23-19) with 2862.10 Kgha-1 were the most expressive.