RESUMEN
El estudio físico del suelo ha recibido atención por su importancia para mantener la producción de caña de azúcar en forma sustentable. Se evaluó la densidad aparente (DAp) en un vertisol en los agrosistemas de caña de azúcar, pastos y selva mediana perennifolia. Para el muestreo de los ciclos de caña se seleccionaron los entresurcos donde no hubo tránsito de equipo, donde pasaron camiones y donde pasó la alzadora durante la cosecha. Se tomaron al azar 9 repeticiones de cada sitio por ciclo de cultivo. Para los agrosistemas de pasto y selva los muestreos se efectuaron al azar con seis repeticiones. La DAp entre 0-10cm de profundidad se determinó con el método del cilindro. Los 11 tratamientos fueron analizados bajo un diseño completamente al azar y contrastes ortogonales. El suelo cultivado con caña sufre mayor compactación durante la cosecha, independientemente del ciclo de cultivo. El camión, por ser más pesado, produce mayor compactación que la alzadora. La DAp se incrementa conforme a los ciclos de cultivo. Los promedios de DAp en los diferentes ciclos de caña no alcanzaron niveles críticos para las raíces (1,60g.[cm.sup.-3]); no obstante, la DAp en el agrosistema de caña superó a la del pasto y la selva. La DAp en el agrosistema de pasto es intermedia entre la selva y la caña, lo que indica que estos suelos, por el agrietamiento en el período de seca y por su reciente formación, poseen buena capacidad de amortiguamiento y explica que durante 20 años su DAp solo se ha modificado en 20% con respecto a la selva.
SUMMARY
The physical properties of soils have received attention for their role in maintaining a sustainable sugarcane production. Under this scheme, the present study was focused on evaluating the apparent density (DAp) of a vertisol soil in sugarcane, pasture and medium perennial rainforest agro-ecosystems was evaluated. Soil samples were taken from the space between furrows of a sugarcane plantation that are used as trails for trucks, trails for crop-lifters, or never affected by machinery; 9 samples were taken at random per crop cycle. Pasture and forest soils were sampled at random with 6 repetitions. DAp at 0-10cm in depth was determined by the cylinder method. Eleven treatments were analyzed by a completely randomized design and orthogonal contrasts. Soils cultivated with sugarcane suffer from higher compaction during the harvest, irrespective of the crop cycle. Truck passage results, due to their heavier weight, in more compaction than crop-lifters. DAp increases with the number of crop cycles. The DAp, averaged over the various cane cycles, did not reach the critical values for the roots (1.60g.[cm.sup.-3]); however, the DAp observed in sugarcane agro-ecosystems surpassed that of pasture and forest soils. The DAp observed in pasture agro-ecosystems is intermediate between the forest and sugarcane, which suggests that soil cracking during the dry season, as well as their recent origin, might give the former a higher dampening capacity. This might also explain why the DAp has only changed 20% in relation to rainforests during the last...