![Sample our Environment & Sustainability journals, sign in here to start your access, latest two full volumes FREE to you for 14 days]({"type":"image" , "src" : "/sda/5935/TOC-Subject-Sample-2021-Environment-Sustainability.jpg"})
Abstract
The availability of a nutrient is related to the soil solution concentration of the nutrient, soil buffer power and the effective diffusion coefficient. A field experiment was conducted at the Rice Research and Extension Center, near Stuttgart, Arkansas to determine these parameters for ammonium (NH4), phosphorus (P), and potassium (K) under the flooded conditions of paddy rice (Oryza sativa L.) and to use these parameters to calculate the relative importance of mass flow and diffusion to nutrient movement to rice roots. Three rice cultivars were grown on a Crowley silt loam. Saturated soil samples were taken from the 0‐ to 40‐cm depth at 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). Labile and solution concentrations, buffer power and effective diffusion coefficients of NH4, P, and K were determined on 5 cm depth increments. In general, labile and solution concentrations of NH4, P, and K were highest in the top 5 cm of soil and decreased with depth. Labile NH4, P, and K concentrations in the top 5 cm depth ranged from 0.17 to 0.91, 0.022 to 0.24 and 0.78 to 4.24 μmol/g, respectively throughout the season. The average NH4 soil solution concentration in the top 5 cm was 0.08 μmol/cm3 and was not affected by sampling date. Solution concentrations of P and K in the top 5 cm ranged from 0.004 to 0.009 and 0.16 to 0.51 μmol/cm3, respectively, throughout the season. Buffer power of NH4 increased with depth and was less than 24 in the top 5 cm throughout the season. Average buffer powers for P and K were 100 and 18, respectively. The average De of NH4, P, and K in the top 5 cm were 1.3 × 10‐6, 2.5 × 107, and 1.2 × 10‐6/cm2/s, respectively, throughout the season. Ammonium diffusion was about 3.6 times faster in the top 5 cm depth increment than in the 35‐ to 40‐cm increment. In contrast, diffusion of P and K did not appear to be affected by soil depth.
The average diffusion distances per day in the top 5 cm depth increment for NH4, P, and K was 0.47, 0.23, and 0.44 cm, respectively. Diffusion is the dominant factor controlling the availability of NH4, P, and K for paddy rice soils.
Notes
Corresponding author. Published with permission of the Arkansas Agricultural Experiment Station.