Manganese in substrate clays—harmful for plants?

Abstract

Mixtures of peat and substrate clays are commonly used as growth media for horticultural plant production. A quality protocol for substrate clays defines a threshold value of active manganese (Mnact = sum of exchangeable and easily reducible Mn) in substrate clays of < 500 mg kg–1 to prevent toxic reactions of plants. This threshold value was tested in experiments with peat‐clay blends under various growth conditions, and nutrient solution experiments were additionally conducted to investigate the effects of silicic acid and dissolved organic matter on the occurrence of Mn toxicity. Common bean (Phaseolus vulgaris L.) and hydrangea (Hydrangea macrophylla) plants were cultivated in different peat‐clay substrates and in peat under different moisture and pH levels. The clays varied in their Mnact content from 4–2354 mg kg–1. The results of the substrate experiments reveal that a threshold value for Mn in substrate clays is not justified, as plants grown in all peat‐clay substrates did not develop any Mn toxicity even at high substrate moisture or low pH conditions which are known to increase the Mn availability. The extraction of active Mn did not well reflect the Mn concentrations in plant dry matter and substrate solution. As plants tolerated high Mn concentrations in the substrate solution compared to the nutrient solution without toxicity symptoms, the influence of silicic acid and dissolved organic matter (DOM) on Mn toxicity was characterized in a nutrient‐solution experiment. Manganese toxicity was clearly diminished by silicic acid application, but not by DOM. The former effect probably explains the tolerance of bean plants in peat substrates where high silicon concentrations in the substrate solution were observed. Peat‐clay blends even provided up to five times more silicon to plants than pure peat.

Effects of steel slag application on greenhouse gas emissions and crop yield over multiple growing seasons in a subtropical paddy field in China

“…Furthermore, the slag itself contained heavy metals, especially Mn, and hence served to increase the supply of these metals to the soil . The observed maximum values of total soil Mn and Co concentrations (314 and 12 mg kg −1 , respectively), though, are well below the thresholds deleterious for growth in plants (Jugsujinda and Patrick, 1993;Kapustka et al, 2006;Shanahan et al, 2007;Mico et al, 2008;Binner and Schenk, 2013).…”

Aplicación líquida edáfica y foliar de manganeso en espinaca (Spinacia oleraceae L.) cultivada en sustrato vermicompost

“…Contenidos menores de 500 mg kg -1 de Mn activo (intercambiable + fácilmente reducido) en los sustratos deben ser garantizados para prevenir reacciones tóxicas en las plantas (Binner y Schenk, 2013). Ese valor está por debajo del sustrato vermicompost usado (566 mg kg -1 ).…”

“…La baja dis-ponibilidad del Mn para las plantas se debe en gran medida a la formación de óxidos insolubles Mn III y Mn IV , constituyendo la fracción dominante del Mn en los suelos (Binner y Schenk, 2013). También, puede ser lavado en suelos áci-dos o de textura arenosa o fijados por óxidos en suelos orgánicos (Gong et al, 2010).…”

Interaction Mechanism of Fe, Mg and Mn in Karst Soil-Mango System

“…Mn poisoning has been demonstrated to occur when the Mn content is higher than 500 mg/kg in soil [19]. However, this toxic effect will be reduced when the high content of Fe and Mg co-exist with Mn in soil [20]. The mechanism of this phenomenon has not been clearly explained until now.…”