Pinnis, U., et al. “Technical, Economical and Ecological Estimation of Up-To-Date Combined Soil Tillage, Fertilising and Sowing Machines”. ENVIRONMENT. TECHNOLOGIES. RESOURCES. Proceedings of the International Scientific and Practical Conference, vol. 1, June 2006, pp. 212-7, https://doi.org/10.17770/etr2003vol1.2009.