Ref1

https://www.researchgate.net/profile/Grzegorz_Zurek2/publication/271380772_The_Effect_of_Sowing_Quantity_and_Row_Spacing_on_Seed_Production_of_Few_Minor_Grass_Species/links/550835f40cf26ff55f804a47/The-Effect-of-Sowing-Quantity-and-Row-Spacing-on-Seed-Production-of-Few-Minor-Grass-Species.pdf