Optimizing black cumin (Nigella sativa L.) productivity under semi-arid conditions: effects of sowing date and seed rate on seed yield and oil content

Abstract

Black cumin (Nigella sativa L.) is a very important medicinal plant; however, its productivity in rainfed semi-arid environments is increasingly threatened by changing climate conditions. Mitigating the negative impacts of climate change may be possible through agricultural practices such as early sowing and seed rate. This study was conducted to determine the effects of different sowing dates and seed rates on the yield and yield parameters of black cumin over two consecutive growing seasons (2021–2022) under rainfed semi-arid climate conditions. The experiment was carried out using a split plot design with five sowing dates (early March to late April) and three seed rates (10, 20, and 30 kg ha−1). Results indicated that sowing date was the primary determinant of crop performance. Early sowing (early to mid-March) significantly extended both vegetative and reproductive phases, resulting in improved plant growth, yield components, and seed filling. This shift in crop development reduced exposure to terminal heat stress and led to the highest seed yield (1,099.3 kg h−1) and oil productivity. Multiple regression analysis revealed that mean temperature during the reproductive phase was the dominant climatic factor limiting yield (P < 0.001), while precipitation had a positive but less pronounced effect (P < 0.01). In addition, seed rate significantly affected yield, with lower seed rate (10 kg ha−1) enhancing both seed yield and oil content by reducing intra specific competition. Delayed sowing shortened the growth cycle and reduced yield by approximately 65%. Despite interannual climatic variability, consistent responses across years indicate that early sowing combined with lower seed rates is an effective strategy to improve productivity under semi-arid conditions. These findings demonstrate that optimizing sowing date and seed rate not only enhances yield and oil content but also provides a practical adaptation strategy to mitigate the adverse effects of climatic stress.