B. HAKYEMEZ, HAKAN, and YASEMIN KAVDIR. “Effects of Some Forage Crops and Mixture on Sunflower Yield and Soil Nitrogen Content”. Asian Journal of Chemistry, vol. 20, no. 3, Mar. 2010, pp. 2251-6, https://asianpubs.org/index.php/ajchem/article/view/19237.