cultivation manihot esculenta 105 starch crops 67 cultivo 48 productivity 34 cultivars 29 root productivity 27 research 26 cultivation systems 23 planting 23 development 22 economics 21 variedades 21 pests 18 weeding 18 cuttings 17 production 16 productividad de raices 16 propagation materials 15 diseases and pathogens 14 harvesting 14 marketing 14 field experiments 13 intercropping 13 propagation 13 soil requirements 13 spacing 13 timing 13 costs 12 estacas 12