Fertilizer, Irrigation, and Natural Ericaceous Root and Soil Inoculum (NERS): Effects on Container-grown Ericaceous Nursery Crop Biomass, Tissue Nutrient Concentration, and Leachate Nutrient Quality

Abstract

We tested the effects of using an inoculum containing natural ericoid roots and soil (NERS) with two fertilizer and irrigation rates on plant growth, shoot (stems and leaves) nutrient concentration, leachate quality, and mycorrhizal colonization of container-grown Coast Leucothoe [Leucothoe axillaris (Lam.) D. Don] and Japanese Pieris [Pieris japonica (Thunb.) D. Don ex G. Don]. Uniform rooted liners were grown in 10.8-L containers in a pine bark, peatmoss, and sand (8:1:1 by volume) substrate medium in a randomized complete block design with four replications. A controlled-release fertilizer, Polyon® Plus 14-16-8 (14N–7P–6.6K), was incorporated in the substrate medium at the 100% manufacturer's recommended fertilizer rate [representing high fertilizer rate (HF)] (56 g per container) to supply 7.84 g nitrogen (N) and at 50% the manufacturer's recommended rate [representing low fertilizer rate (LF)]. Plants were irrigated using a cyclic drip irrigation system at high (HI) and low (LI) irrigation rates calibrated to supply 25.2 L of water and 16.8 L per week, respectively. On average, NERS inoculation increased shoot growth of Leucothoe and Pieris by 56% and 60%, respectively. Shoots of Leucothoe inoculated with NERS had higher N, phosphorus (P), magnesium (Mg), and manganese (Mn) concentrations than non-inoculated plants. At LF, nitrous-N (NOx-N) and orthophosphorus (PO4-P) concentrations in the leachate were reduced by 53% from Leucothoe and 62% from Pieris compared with HF-treated plants. A reduction of 37% and 36% in PO4-P concentration in leachates from Leucothoe and Pieris, respectively, were achieved at the reduced irrigation (LI) rate. The NERS inoculation reduced PO4-P concentrations in leachate from Leucothoe by 26% and NOx-N concentration by 33% in leachates from Pieris compared with non-inoculated plants. Compared with plants grown in the HI–HF treatment, the combination of LI–LF treatment reduced NOx-N concentrations in leachates from Leucothoe by 60% (P = 0.016) and reduced PO4-P leachate concentrations from Pieris by 72% (P = 0.0096). Decreasing the fertilizer rate to 50% of the recommended rate and the irrigation rate to 67% of the recommended rate in conjunction with the incorporation of NERS reduced leachate nutrient concentrations of two main water pollutants (NOx-N and PO4-P). Adopting the practice of adding NERS containing fungi and bacteria can be an effective system to increase shoot dry weight, allow reduction in fertilizer application, conserve water for irrigation, and minimize subsequent nutrient runoff in nursery operations.