Evaluation of pollination modes on Nigella sativa yield and seed quality, with analysis of farmer practices in Northern Ethiopia

Pollination services are essential for crop productivity, yet their role in supporting both yield and nutritional quality remains understudied in many spice crops, especially under smallholder farming conditions. For Nigella sativa (N. sativa, black cumin)—Ethiopia’s second-largest spice export—no comprehensive assessment has measured how pollination influences productivity and seed quality, nor has it examined how farmer practices align with these biological needs. We combined a controlled field experiment with a household survey to address this gap in black cumin cultivation in Northern Ethiopia. The experiment employed a randomized block design with three treatments: honeybee-only pollination, open pollination, and pollinator exclusion, and compared phenological, agronomic, and seed quality traits. Honeybee‑only pollination increased seed yield by 49.1% (95% CI: 45.3–52.8%), protein content by 43.4% (95% CI: 39.7–47.1%), and germination by 60.5% (95% CI: 56.2–64.8%) compared to exclusion. Effect sizes were very large (Cohen’s d > 5 for phenological traits; η2 > 0.97 for quality parameters), indicating that pollination explained most of the observed variation. Open pollination provided intermediate benefits (yield + 42.4% over exclusion), but managed honeybee colonies added further gains (yield + 4.7%, protein + 14.6%). Floral visitor observations in the open-pollinated treatment showed that honeybees dominated floral visits (64%), with foraging peaking at 11:00–12:00. However, the farmer survey found that 74% of farmers applied pesticides during this peak period, and 93.3% had limited knowledge of pollination services. These practices could diminish the benefits observed in the experiment. This is the first study to demonstrate that managed honeybees pollinate N. sativa and that their pollination significantly improves yield and seed quality. Still, the disconnect between pollinator activity and pesticide use suggests these benefits may not reach smallholder farmers. Bridging the gap between ecological services and farmer practices through targeted extension and pollinator‑friendly management could unlock significant productivity and quality gains for Ethiopia’s spice sector.