Transport of bromide under intermittent and continuous ponding conditions

An understanding of water and chemical transport through the soil iscrucial for the development of proper irrigation and nutrient management practices. Because of natural heterogeneity and variability of soils, results often cannot be extrapolated between sites and from laboratory to field. In this study, transport of bromide (Br-) was investigated in a silt loam soil under intermittent and continuous pondingconditions using 10 pairs of stations in a 0.40-ha field. Each station consisted of a double ring infiltrometer and three solution samplers installed at 30, 60, and 100 cm depths. A 3-cm pulse of KBr- with an average Br- concentration of 500 ppm was applied to each station. Upon depletion of the pulse, 8 cm of water was ponded in each infiltrometer. For the continuous ponding stations, water was added daily and infiltrated volume was recorded. For each intermittent treatment, the time between subsequent irrigations was equal to the time for complete 8 cm infiltration plus 7 d of redistribution time. Solution samples were collected from all samplers on a daily basis for 3 mo, and analyzed for bromide concentration in the lab. At 30-cm depth, the mean tracer velocities for intermittent and continuous ponding treatments were larger than piston flow velocities by factors of 2.05 and 1.57, respectively. Solute velocities decreased with depth for both treatments. Nutrient management models based on piston flow velocities mayoverestimate the mass of available nutrients to plants in the root zone. [ABSTRACT FROM AUTHOR]