ROOT DYNAMICS IN PLANT AND RATOON CROPS OF SUGAR-CANE

The root system of a sugar cane crop on an Ultisol in northeastern Brazil was examined throughout the plant and first ratoon crop cycles, using both coring and minirhizotron methods. Total root masses (living plus dead, 0.9-1.1 kg m-2) and live root lengths (14.0-17.5 km m-2) were greater during the ratoon cycle than at the end of the plant cane cycle (0.75 kg m-2 and 13.8 km m-2, respectively). Root die-back during the two weeks following ratoon harvest was estimated to be 0.15 kg m-2, about 17% of the total root mass. Root die-back after the plant cane harvest was lower because fire was not used at this harvest and soil humidity was higher under the accumulated litter. A small amount of fine roots proliferated in the litter layer, amounting to 1% of the total mass and 3% of the total length. Root turnover could not be accurately assessed from minirhizotron observations due to variation in the relationship between coring data and the minirhizotron data with both time and soil depth.