BIOMASA RADICAL DE PASTOS BAJO LABRANZA Y FERTILIZACIÓN EN UN INCEPTISOL DEL VALLE DEL SINU

Angleton grass (Dicanthium aristatum) is the dominant Gramineae specie in the Sinu River Valley. Its root growth is limited by soil compaction, a mixed effect of high density and penetration resistance. With the aim to determine the effect of vertical tillage and fertilization over root biomass, soil density and penetration resistance, four different kinds of grasses (Mulato II, Toledo, Angleton and Estrella) were established on an inceptisol soil located at Turipaná Research Center, in Cereté, Córdoba, Colombia. Four vertical tillage treatments with three repeats were evaluated: two with rigid chisel, 30 cm - 60 cm and two with grassland renovator, horizontal distance 30 and 60 cm, and 30 cm depth. Two levels of fertilization were evaluated: F1: 300 kg ha-1 of DAP (18% N - 46% P2O5), 200 kg ha-1 of KCl (60% K2O) and 150 kg ha-1 of urea (46% N) and F2: 50% of the previous described treatment. In a split plot design experiment, the effect of vertical tillage and fertilization during 18 months over soil density, penetration resistance and root biomass growth were tested by ANOVA and average Duncan comparison. No independent effect of tillage or fertilization on grasses was observed, but there are significant interaction between tillage and grasses, fertilization and grasses and tillagefertilization and grasses. It is concluded that differences in the variables soil density, penetration resistance and root biomass were due to grazing effect and tillage-fertilization-grass interaction.