NUTRIENT-UPTAKE RELATIONSHIP TO ROOT CHARACTERISTICS OF RICE

Data on root parameters and distribution are important for an improved understanding of the factors influencing nutrient uptake by a crop. T herefore, a study was conducted on a Crowley silt loam at the Rice Res earch and Extension Center near Stuttgart, Arkansas to measure root gr owth and N, P and K uptake by three rice (Oryza sativa L.) cultivars a t active tillering (36 days after emergence (DAE)), maximum tillering (41 DAE), 1.25 cm internode elongation (55 DAE), booting (77 DAE) and heading (88 DAE). Soil-root core samples were taken to a depth of 40 c m after plant samples were removed, sectioned into 5 cm intervals, roo ts were washed from soil and root lengths, dry weights and radii were measured. Root parameters were significantly affected by the soil dept h x growth stage interaction. In addition, only root radius was affect ed by cultivar. At the 0- to 5-cm soil depth, root length density rang ed from 38 to 93 cm cm(-3) throughout the growing season and decreased with depth to about 2 cm cm(-3) in the 35- to 40-cm depth increment. The increase in root length measured with each succeeding growth stage in each soil horizon also resulted in increased root surface area hen ce providing more exposed area for nutrient uptake. About 90% of the t otal root length was found in the 0- to 20-cm soil depth throughout th e season. Average root radius measured in the 0- to 5-cm and 35- to 40 -cm depth increments ranged from 0.012 to 0.013 cm and 0.004 to 0.005 cm, respectively throughout the season. Total nutrient uptake by rice differed among cultivars only during vegetative growth. Differences in total nutrient uptake among the cultivars in the field appear to be r elated to absorption kinetics of the cultivars measured in a growth ch amber study.