Phosphorus Rate, Leaching Fraction, and Substrate Influence on Influent Quantity, Effluent Nutrient Content, and Response of a Containerized Woody Ornamental Crop

Abstract

Production of containerized nursery crops requires high inputs of water and mineral nutrients to maximize plant growth to produce a salable plant quickly. However, input efficiencies remain below 50% resulting in major quantities of water and nutrients leached. This study was conducted to determine if production factors could be altered to increase water and phosphorus uptake efficiency (PUE) without sacrificing plant growth. The effects of a pine bark substrate amendment (clay or sand) and a 50% reduction in both P application rate (1.0 g or 0.5 g) and leaching fraction (LF = effluent ÷ influent) (0.1 or 0.2) were investigated. Containerized Skogholm cotoneaster (Cotoneaster dammeri Schnied. ‘Skogholm’) was grown on gravel floor effluent collection plots that allowed for calculation of water and nutrient budgets. Pine bark amended with 11% (by vol.) Georgiana 0.25 to 0.85 mm calcined palygorksite-bentonite mineral aggregate (clay) increased available water 4% when compared with pine bark amended with 11% (by volume) coarse sand. Decreasing LF from 0.2 to 0.1 reduced cumulative container influent 25% and effluent volume 64%, whereas total plant dry weight was unaffected by LF. Reduction of target LF from 0.2 to 0.1 reduced dissolved reactive P concentration and content by 8% and 64%, respectively. In a sand-amended substrate, total plant dry weight decreased 16% when 1.0× P rate was reduced to 0.5× P, whereas total plant dry weight was unaffected by rate of P when pine bark was amended with clay. Plant content of all macronutrients, with the exception of N, increased when pine bark was amended with clay versus sand. Reducing P rate from 1.0× to 0.5× increased PUE 54% or 11% in a clay or sand-amended substrate, respectively. Amending pine bark with 11% (by volume) 0.25 to 0.85 mm calcined palygorksite-bentonite mineral aggregate produced an equivalent plant with half the P inputs and a 0.1 LF, which reduced water use 25% and P effluent losses 42% when compared with an industry representative substrate [8 pine bark : 1 sand (11% by volume)].