The use of rock dust as a natural media amendment for the production of horticultural crops in controlled environments

Armah, Abraham (2021) The use of rock dust as a natural media amendment for the production of horticultural crops in controlled environments. Masters thesis, Memorial University of Newfoundland.

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Abstract

Rock dust (RD) is a by-product of the mining industry generated after extracting precious minerals like gold. However, RD has low commercial use and is typically stocked-piled at mine sites for disposal. Potentially, RD contains macro- and micronutrients required for crop growth. Thus, RD could be a valuable substrate for amending crop growth media, thereby improving productivity and enhancing economic and environmental benefits. This study aimed to evaluate the potential of RD as a natural soil amendment for improving media quality, agronomic performance, and nutritional quality of vegetable crops produced under controlled environmental conditions. The controlled environmental pot experiments were carried out in a walk-in growth chamber located at Grenfell Campus, Memorial University of Newfoundland. Experimental treatments contained 10 different media formulations amended with RD and were denoted as follows: 1) 100%Rock dust (RD), 2) 50%Rock dust+50% Topsoil(RDT), 3) 50%Rock dust+ 25%Biochar + 25% Promix (RBP) 4) 100%Topsoil(TS), 5) 25%Rock dust + 75% Topsoil(RT), 6) Huplaso (H) (negative control), 7) 50%Rock dust+ 25% compost +25% Promix (RCP)8)50%RD+ 50%Promix (RP), 9) Promix (Control), 10) 50%Rock dust + 50%Biochar(RB). The experiment was a completely randomized design (CRD) with four replications and three crops (amaranth, kale, and lettuce) per treatment. Agronomic performance evaluated included chlorophyll content, root shoot ratio, biomass yield etc.), growth media quality included active microbial community structure, mineral composition, porosity, bulk density, pH, and field capacity.), and crop nutritional quality was represented by phenolic content, antioxidant activity, mineral nutrients, and fatty acid composition. We observed six different microbial communities, namely G+ & G- & Fungi (F), protozoa, and eukaryote, and a strong relationship between the physicochemical properties of the media and the active microbial composition. These include high correlations between the bulk density and the microbial composition. The best agronomic performance was observed in RCP, RBP, RB, and RP. This includes increased total biomass, chlorophyll content, number of leaves, and fresh weight. The RD-based media amendments, RCP, RBP, RB, and RP successfully modulated horticulture crop nutritional composition (fatty acids, protein, minerals, and antioxidants). We next tried to assess the relationship between media quality and how this influences the crop agronomic performance and nutritional quality. We observed substantial positive correlations(r=0.88) of BD (bulk density) with RSR (root-shoot ratio), a negative correlation(r=-0.81) of BD with G+&G-&F, a positive correlation(r=0.74) of porosity with FW (Fresh weight), and strong positive correlation of TBM (Total biomass) with MUFA (Monosaturated fatty acid) and a strong positive correlation of BD with total macro minerals in the plant tissue. Mechanistically, the strong associations observed between the media quality and crop agronomic performance as well as nutritional quality suggest that RD-based media have superior bulk density, porosity, nutrient composition, and microbial composition. This resulted in crops having an enhanced capacity to absorb nutrients from the media mineralized by G+&G-&F and translocate this into superior biomass and bioaccumulation of the following nutrients: protein, MUFA, total antioxidant, and total macronutrients. Our results demonstrate that using RD as natural media amendment could provide a cost-effective way of providing a high-quality growth media for producing vegetables with superior yield or biomass and improved nutritional quality under controlled environmental conditions. RD-based natural media amendments could provide a sustainable alternative for the by-product disposal.

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