Upward flux of water and deep-placed P in relation to soil texture, water table depth and evaporation rate

Abstract

SummaryUpward flux of water and deep-placed (8–10 cm) P was studied in columns of sandyloam and silty clay loam, with water tables of 60 and 90 cm, each subjected to potential evaporation rates of 2–2 and 7–5 mm/day, for 15 days. An amount of 300 mg P/kg soil, labelled with 20 /tCi 32P/g P, was applied as diammonium hydrogen orthophosphate.Evaporation losses increased with increase in potential evaporation (PE) and decrease in depth to water table in both soils, but the ratio of actual to potential evaporation (AE/PE) decreased with increasing PE, indicating that the evaporative losses in both the soils were mainly controlled by their hydraulic conductive properties. Under no circumstances did AE equal PE. Evaporation, in general, was higher from sandy loam than from silty clay loam.Corresponding to water flux, total upward P flux increased with increasing PE and decreasing depth to water. In the sandy loam, with 2–2 mm PE/day, 21 % of the deepplaced P moved to the soil surface with the 60 cm water table, against 5 % with the 90 cm water table. Under 7–5 mm PE/day, 39% P migrated to the surface with the 60 cm water table, but no 3aP was detected at the surface with the 90 cm water table. In the silty clay loam, however, P movement was much restricted.