Abdl Alazez, N. K. ., Moter, R. M. ., & Hassan, A. Z. (2012). Effect of nitrogen and phosphorus fertilzation and planting dates on growth, flower yield and methoxalen conceration in Calendula officinalis L. Journal of Biotechnology Research Center, 6(1), 10–18. https://doi.org/10.24126/jobrc.2012.6.1.190