Effect of chemical and organic fertilisation on pollinators of Abelmoschus esculentus Moench (Malvaceae) in Ngaoundéré (Adamawa-Cameroon)

Abstract

Abelmoschus esculentus is a very important cultivated annual crop, in tropical and mediterranean areas. Its fruit presents a vast morphological and phenological variabilities; its flowering period is continuous all around the year but highly dependent on biotic and abiotic factors. This study was conducted to understand the influence of chemical and organic fertilisation on the variation of entomophilous insect of A. esculentus in the Adamawa region in Cameroon. Investigations were carried out during two consecutive agricultural campaigns both in dry and wet seasons on an area of 400 m² in Ngaoundere. Three cropping processes were carried out: cultivation of okra with chemical fertiliser and regular weeding; cultivation of okra with organic fertiliser, consisting of a local made compost with regular weeding; and cultivation of okra whit no fertilisation (negative control). 60 plants were randomly selected and labelled per treatment. The aim was to count for 8 times periods the different pollinating insects present on the flowers of A. esculentus for each treatment in the two seasons. Measurement of pollen grains diameter was done on 40 pollen grains for each treatment. A total of 40 flowers were selected per treatment to evaluated sugar concentration in the nectar. Results showed that a total of 27 insects were pollinators of okra in Ngaoundere, most abundant in rainy season compare to dry season. The main pollinators varied with the season. Plants fertilised with compost were more attractive in the rainy seasons than the dry season; organic fertilisation enhanced pollinator’s visits. Moreover, pollen from these plants were larger. This study rises up that, organic fertilisation leads to plants with most attractive flowers containing large pollen grains which are finally most pollinated. In both seasons, nectar from compost-amended flowers contained higher sugar concentration.