[Superficial drainage and conservation tillage under a system of crop rotation]

abonos fosfatados application rates broadcasting cosecha crotalaria densidad del suelo dose d'application drainage de surface drenaje de superficie evaluation fallow systems fertilisation fertilizer application field experimentation genetic soil types glycine max harvesting labranza phosphate fertilizers rotation culturale rotational cropping sistemas con barbecho site preparation soil density surface drainage tillage travail du sol venezuela zea mays