Use of pulp mill ash as a substrate component for greenhouse production of marigold

Abstract

Pulp mill ash was evaluated as a substrate component in the production of greenhouse-grown French marigold (Tagetes patula L. 'Janie Deep Orange'). Peat-based substrates (75:10:15 by volume blend of peatmoss, vermiculite, and perlite) amended with 0% to 50% (by volume) pulp mill ash were compared with a standard commercially available substrate. With the exception of an unfertilized control, each substrate blend contained 5.93 kg·m-3 14N-6.2P-11.6K (3- to 4-month release) and 0.89 kg m-3 Micromax. Substrates containing higher volumes of ash had finer particles, less air space, and more waterholding capacity than the commercial substrate. Bulk density increased with increasing ash volume, and substrate containing 50% ash had 120% greater bulk density than the commercial substrate. Substrates containing ash generally had higher pH and electrical conductivity (EC) than the commercial substrate with substrate pH and EC increasing with increasing ash volume. In general, marigold plants grown in peat-based substrates with the addition of 0% to 50% ash had similar growth indices, flower dry weights, numbers of flowers, and SPAD values as plants grown in commercial substrate; however, plants grown in substrates containing 30% to 50% ash had lower shoot dry weights or root quality ratings than plants grown in commercial substrate. Plant growth index, shoot dry weight, and root quality rating decreased with increasing ash volume.