Kurayemen, C., P. I. Agber, and A. Aminu. “ASSESSMENT OF SOIL MANAGEMENT PRACTICES ON SOIL PRODUCTIVITY USING RIQUIER PRODUCTIVITY INDEX MODEL IN MAKURDI, BENUE STATE, NIGERIA”. Academic Journal of Current Research, vol. 7, no. 4, Apr. 2020, pp. 46-53, http://cirdjournals.com/index.php/ajcr/article/view/308.