Organic and inorganic fertilization differently affect the agronomic performance of two okra (Abelmoschus esculentus L. Moench) varieties and soil fertility
Abstract
Okra is a key vegetable in West Africa, but poor fertilization practices and low soil fertility constrain its productivity. This study evaluated the responses of two okra varieties (AVOK1504 and Konni) to twelve fertilization treatments, including poultry manure (PM), foliar biostimulant (ABC grower), NPK, Urea, and K 2 SO 4 , applied alone or in combination. A split-plot design with three replications was used, with “Variety” as the main factor and “Fertilizers” as the sub-factor. The field trial was implemented over two seasons (years 2021 and 2022) at Abomey-Calavi (Southern Benin) with Sudano-Guinean climatic conditions. Growth parameters, yield components, soil properties, and climatic data were collected. Analysis of variance with the least significant difference at p < 0.05, was performed to assess statistical differences in growth parameters, yield, and yield components. Fertilization regimes significantly influenced plant height, stem diameter, branching, and leaf development ( p < 0.001). T2 induced early flowering and fruiting for the Konni variety, whatever the season: respectively 38.3 and 39.3 days after sowing (season1) 47 and 48 days after sowing (season2). Konni yielded significantly higher than AVOK1504 regardless the season ( p < 0.001). Sole organic fertilizer and its combinations with mineral fertilizers enhanced growth and yield, with 10 t/ha PM (T2), 10 t/ha PM + 200 kg NPK + 50 kg Urea + 50 kg K₂SO₄ (T6) and T7 (T6 + 250L/ha ABC grower) achieving the highest yields: 4.3 t/ha, 5.3 t/ha and 5.8 t/ha, respectively, for Konni against 5.1 t/ha, 4.8 t/ha and 5.3 t/ha, respectively, for AVOK1504. Sole PM at 10 t/ha (T2) showed similar statistical yield performance as T6 and T7, despite its low inputs composition, and additionally most effectively enhanced soil pH, total N, Ca, and Mg. Notably, none of the treatments increased soil organic carbon or available phosphorus, an unexpected result given the high carbon content of the PM applied. Findings highlight the agronomic benefits of integrated nutrient management for optimizing okra productivity and soil health. These results inform fertilizer recommendations and sustainable soil fertility management strategies for okra-producing regions in Benin and similar agroecological zones.