Berzins, P. et al. 2015. The Productive Longevity Of Perennial Grasses Swards Depending On The Npk Fertilizer Rates. ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference. 2, (Aug. 2015), 244–251. DOI:https://doi.org/10.17770/etr2011vol2.967.