Micronutrient Fe and Mn uptake from peat by marigold and petunia

Abstract

Peat substrates have the potential to function as micronutrient sources such as iron (Fe) and manganese (Mn). Typically, when planning fertilization program for crops, the components of peat substrates are not taken into account. The objective was to quantify potentially plant-available micronutrients of Fe and Mn from peat substrates by floriculture species when no additional Fe and/or Mn were applied in the fertilizer solution. Greenhouse experiments were conducted using Tagetes erecta ‘Atlantis Primrose’ marigold (iron-efficient) and Petunia x hybrida ‘Celebrity Pink Morn’ petunia (iron-inefficient) to compare extractable Fe and Mn from two peat sources with actual plant uptake of these nutrients by the plants. In Experiment 1, marigold was grown hydroponically in plastic tubs using four different nutrient solutions: complete, without Fe, without Mn, and without both Fe and Mn. Within a period of less than two weeks after transplant, the absence of Fe and Mn severely limited marigold growth. The hydroponic study highlighted the importance of providing both Fe and Mn nutrients immediately after sowing to support normal marigold growth. In Experiment 2, both marigold and petunia were grown from seed in two peat substrates (Blackmore seedling peat “BM peat” and Sunshine Professional Black Bale peat “SG peat”) and an acid-washed sand substrate. Each peat was limed at 3 g.L−1 of reagent grade CaCO3 resulting in an initial substrate-pH of 5.0 for SG peat and 5.5 for BM peat. Four nutrient solutions [(a) complete, or complete with (b) no Fe, (c) no Mn, and (d) no Fe or Mn] were applied with each irrigation without leaching. Initial substrate nutrient levels were extracted using the SME (saturated medium extract) method using either water (SMEW) or 0.005 M DTPA (diethylenetriamine-pentaacetic acid, SMED) as extractants. Over a 5-week period (during the vegetative, non-blooming stage), peat substrates provided sufficient Fe and Mn for marigold, but iron deficiency symptoms were observed in marigolds grown in sand without Fe fertilizer. Petunia plants developed iron deficiency symptoms in all substrates without Fe fertilizer. The absence of Mn fertilizer, however, did not have a significant impact on petunia growth and health, indicating that peat substrates likely provided adequate Mn for non-symptomatic petunia plant growth. The micronutrient Fe and Mn budget analysis suggested that the SMEW method underestimated the availability of Fe and Mn to the plants, whereas the SMED method may have overestimated the extractable Fe and Mn levels in relation to the actual tissue uptake. Overall, the peat substrates showed a high potential for providing Fe and Mn in quantities sufficient for the initial growth of iron-efficient marigold, but was inadequate for iron-inefficient petunia.