Industrial mineral aggregate amendment affects physical and chemical properties of pine bark substrates

Abstract

Nonpoint source effluent containing nitrate N (NO3-N) and phosphorus (P) from containerized nursery production has garnered local, regional, and national concern. Industrial minerals have long been used as absorbents, agrochemical carriers, and barriers to retain heavy metals. Our objective was to determine the effects of a palygorskite-bentonite industrial mineral aggregate on the physical and chemical properties of a soilless substrate and the resulting impact on water and nutrient efficiency. The mineral aggregate had two particle size ranges (0.25 to 0.85 mm or 0.85 to 4.75 mm) in combination with two temperature pretreatments [low volatile material (LVM) or regular volatile material (RVM)]. A representative substrate (8 pine bark:1 coarse sand) of the southeastern United States nursery industry was also included in the study as a control. Cotoneaster dammeri C.K. Schneid. 'Skogholm' was grown in all substrates on collection pads that allowed for the quantification of daily influent and effluent volumes to calculate cumulative NO3-N, ammonium N (NH4-N), and dissolved reactive phosphorus (DRP) loss for 112 days. There was a 13% to 15% decrease in daily water application volume with no effect on Skogholm cotoneaster growth, which equated into a savings of 22 to 26 L per 14-L container in mineral aggregate-amended substrates compared with a sand-amended substrate (control). Mineral aggregate-amended substrates decreased NH4-N and DRP effluent 39% and 34%, respectively, compared with the control. In addition, LVM and particle size 0.25 to 0.85 mm reduced effluent DRP compared with the 0.85 to 4.75-mm RVM aggregate. Plant dry weight was unaffected by any of the treatments. Substantial nutrient content reduction in effluent and reductions in water application were achieved with amending pine bark with 0.25 to 0.85 mm LVM industrial mineral aggregate. A 0.25 to 0.85-mm LVM industrial mineral aggregate pine bark-amended substrate reduced effluent DRP and NH4-N greater than 40% and reduced water application 15% or 26 L when compared with the industry representative substrate.