Effect of pH on Foliar Uptake of 2,4,5-T-1-14C

Abstract

Uptake of 2,4,5-T-1-14C [(2,4,5-trichlorophenoxy)-acetic acid] by immersion of honey mesquite [Prosopis juliflora(Swartz) DC var.glandulosa(Torr.) Cockerell] leaflets rapidly diminished as pH was increased from 3.5 to 9.5. Uptake diminished less rapidly as pH increased when 10-μl droplets were applied to leaflets that were kept moist. Uptake was equivalent from solutions of pH 3.5, 5.5, and 7.5; but severely reduced at pH 9.5, when leaflets were droplet treated and let dry. Uptake under dry conditions from pH 7.5 and 9.5 droplets containing 1 M NH4Cl was equivalent to uptake from pH 3.5 and 5.5 droplets lacking NH4Cl. NH4Cl had no enhancing effect on uptake at any pH when leaflets were immersed or droplet-treated and maintained moist. Low concentrations of urea had no enhancing effect on uptake at pH 9.5 by droplet-treated leaflets that were allowed to dry. Urea concentrations above 0.1 M inhibited uptake.