Influence of phosphorus and soil amendments on black seed (Nigella sativa L.) oil yield and nutrient uptake

• PUE in alkaline or calcareous soils highly depends on the plants ability to uptake P from the soil.
• There was a positive correlation between soil available P with P and N concentrations in plants.
• Oil and essential oil yields of black seed were affected by soil amendments.
• For every unit increase in PHI, seed yield increased.
• There was a negative correlation between PAE, PUTE and PUE with grain yield.

In order to investigate the effects of sulfur (S) oxidation and vermicompost (V) application on black seed (Nigella sativa L.) oil yield and its nitrogen and phosphorus uptake, a two-year field experiment was conducted at Faculty of Agriculture, Ferdowsi University of Mashhad, Iran in a calcareous soil during 2013 and 2014. A randomized complete block design arranged in factorial with four replications was used to analyze 12 treatments. The calcareous soil amendments (control, V + Thiobacillus thiooxidans (T), S + T and V + S + T) and three levels of P (0, 30 and 60 kg ha−1) were considered as the first and the second experimental factors, respectively. All calcareous soil amendments (V+ T, S+ T and V + S + T) caused a significant reduction in soil pH, and a significant increase in electrical conductivity (EC). In addition, calcareous soil amendments showed a considerable effect on soil available P content. The highest grain, oil and essential oil yields were obtained from V + S + T treatment. The soil amendments significantly increased N and P concentration in plants and improved P harvest index. Although a positive correlation was observed between P and N concentration, there was a negative correlation between grain yield and P use efficiency. It seems that any approach that would allocate more P to seeds, during seed development on the mother plants, would increase final yield in black seed.