Dr Sjoerd W. Duiker is Professor of Soil Management and Applied Soil Physics at Penn State University, USA. He has made significant contributions to both research and extension in developing more sustainable soil management practices in such areas as no-till systems, the use of cover crops, mulches and more diverse crop rotations. He is a member of the Governing Board of the Northeast Cover Crops Council which brings together universities, farmers, government agencies and others to optimise cover crop use in the north-eastern states of the USA.

Dr Andy Clark recently retired as National Communications Director of the United States Department of Agriculture (USDA) Sustainable Agriculture Research and Education (SARE) Program. He led the communications arm of the SARE Program that was instrumental in developing and disseminating sustainable crop and livestock management practices in the United States. As Communications Director, Dr Clark oversaw the development of more than 40 publications, including editing the Third Edition of the SARE publication Managing Cover Crops Profitably, widely regarded as the standard reference for farmers, agronomists and others interested in adoption of cover crops on farms in the United States.