Msuya, C.P.; Duvel, G.H. (Gustav Heinrich)(South African Society for Agricultural Extension, Department of Agricultural Ecomomics, Extension and Rural Development, University of Pretoria, 2007)
Jibba, K.B.; Duvel, G.H. (Gustav Heinrich)(South African Society for Agricultural Extension, Department of Agriculture, Ecomomics, Extensions and Rural Development, University of Pretoria, 2008)
Zwane, E.M.; Duvel, G.H. (Gustav Heinrich)(South African Society for Agricultural Extension, Department of Agriculture, Ecomomics, Extensions and Rural Development, University of Pretoria, 2008)
Duvel, G.H. (Gustav Heinrich)(South African Society for Agricultural Extension, Department of Agriculture, Ecomomics, Extensions and Rural Development, University of Pretoria, 2008)
Duvel, G.H. (Gustav Heinrich)(South African Society for Agricultural Extension, Department of Agricultural Ecomomics, Extension and Rural Development, University of Pretoria, 2007)