Vigovskis, Janis, Aivars Jermuss, Agrita Svarta, and Daina Sarkanbarde. “The Changes of Nutrient Content in Soil in Long-Term Fertilizer Experiments”. ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference 2 (June 17, 2015): 329–332. Accessed May 2, 2024. https://journals.rta.lv/index.php/ETR/article/view/624.