Abstract
Peat is the most common substrate used in nurseries despite being a very expensive and a non-renewable material. Peat replacement with biochar could be a sound environmental practice, as it is produced from waste biomass, but evaluation of biochar as a potting substrate is needed. Ratios of peat:biochar of 100:0, 70:30, 30:70 (BC0, BC30, and BC70, respectively), two fertilizer rates (FERT1, FERT2), and arbuscular mycorrhizal fungi (AMF) inoculation were tested on potted Pelargonium plants. Plant growth, flowering, bio-physiological and nutritional responses, and root mycorrhization were evaluated. The BC30 mixture did not affect plant growth compared with pure peat. However, BC30 in combination with FERT2 treatment was more effective in enhancing nitrogen (N) and chlorophyll (CHL) leaf concentrations, and leaf and flower numbers. The BC70 mixture depressed plant growth, flowering traits, and root mycorrhization. Leaf N concentration was below the sufficiency range reported for Pelargonium growth. Leaf concentration of phosphorous (P) was adequate in pure peat and in BC30 but it dropped close to sub-optimal values in BC70. The pH value of the mixtures lowered P availability, though in BC30 the mycorrhizal activity could have allowed adequate P plant uptake. In BC70 plants, the deficiency of both N and P might be a reason for the observed growth reduction. The inoculation of the substrate with selected AMF improved plant growth (higher dry biomass, greater floral clusters, larger and more abundant leaves) and quality resulting in unstressed (lower electrolyte leakage and higher relative water content values) and greener leaves (low L∗ and C∗, high CHL content) and in more intensely colored flowers. We conclude that biochar can be applied in nursery/potted plant production provided that the proportion in the peat mixture does not exceed 30%. Furthermore, AMF inoculation contributed to achieving the best plant performance in 30% biochar amended medium.
Highlights
Biochar (BC) is produced via hydrothermal carbonization from a wide range of biomass sources including agricultural wastes, green-waste, and animal manures
The pH of BC30 and BC70 were almost one pH unit greater compared with the pure peat (BC0)
Biochar increased EC, bulk density (BD), air space (AS) and, when added at the highest proportion, it reduced total porosity (TP) and the water-filled porosity (WFC) of the substrate
Summary
Biochar (BC) is produced via hydrothermal carbonization from a wide range of biomass sources including agricultural wastes, green-waste, and animal manures (biomass feedstock). The positive effects of biochar application to agricultural soils are Biochar mixtures enhance Pelargonium growth linked to changes in soil physical and chemical parameters leading to increased water-holding capacity, reduction of bulk density (BD), and addition of cation exchange sites (Laird, 2008). By serving as a source of reduced carbon compounds and by increasing the availability of micronutrients, biochar may be beneficial to microbial populations such as arbuscular mycorrhizal fungi (AMF; Warnock et al, 2007; Solaiman et al, 2010; Lehmann et al, 2011). Above a certain threshold of application in the soil, biochar may decrease AMF root colonization (Warnock et al, 2010; Hale et al, 2013; LeCroy et al, 2013; Mukherjee and Zimmerman, 2013)
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