Organic soil fertility amendments and tritrophic relationships on cabbage in Uganda: Experiences from on-station and on-farm trials

Organic soil fertility amendments may have direct or indirect pest management properties through an impact on crop characters and/or the pest’s natural enemies. This study was carried out to assess the effect of utilizing market crop wastes (MCW) as soil fertility amendments on tritrophic relationships of cabbage. The study was conducted on-station for three consecutive seasons; and was verified on-farm for one season. Treatments included 1) MCW compost incorporated in soil; 2) Un-composted MCW incorporated in soil; 3) Un-composted MCW on the soil surface; 4) a chemical fertilizer (NPK) incorporated in the soil; and 5) the un-amended control. The treatments were arranged in a randomized complete block design with three replications. The MCW were applied at a rate of 12 tonnes/ha. Data was collected on plant attributes, pest population dynamics of two pest guilds, natural enemies, and cabbage yield. Results indicated that MCW compost amended plants consistently had the highest aphids and diamondback moth infestations; the highest natural enemies’ counts and the highest cabbage yield. Correlations revealed that the soil fertility amendments had effects that cascaded to different trophic levels.