Chukwuemeka K., Anayo N. I., in Ogechi A. „Multifactor Productivity of Smallholder Yam Farmers in Ebonyi State, Nigeria“. Agricultura Scientia, Let. 16, št. 1-2, november 2020., str. 19-25, doi:10.18690/agricultura.16.1-2.19-25.2019.