Abstract
Professional peat-free substrates for ornamental plant production are increasingly required by nursery growers. Most promising materials are green compost, coconut coir dust, and woody fibre, used alone or in mixtures. One of the major concerns is pH, usually higher than optimal. In this work, a method based on a three-step procedure was adopted to acidify three organic matrices alone or in mixtures and to individuate the most suitable product, between iron(II) sulphate 7-hydrate and elemental sulphur chips. Firstly, the determination of the buffering capacity by dilution with sulphuric acid was carried out to determine dosages. Afterwards, an incubation trial of 84 (iron(II) sulphate) or 120 days (sulphur chips) was conducted on matrices and substrate mixtures with calculated doses in a climatic chamber maintained at 21 °C. Iron(II) sulphate resulted not suitable because it caused a rapid, but not lasting, pH lowering and an excessive electrical conductivity (EC) increase. Sulphur chips could instead guarantee an adequate and lasting pH lowering. These results were then validated in the open field trial on matrices and substrates. The proposed acidification methodology could be considered in developing new substrates, but the rapidity of pH acidification and EC increase on plant and mineral nutrition should be further investigated.
Highlights
The valorization of organic waste in ornamental growing media has been recently grown in order to replace peat-based substrates in this sector [1]
As well as growing media containing compost, reported higher pH and electrical conductivity (EC) values compared with coconut coir dust and stabilized wood fibre (Table 1)
In previous works pH adjustment trials were conducted on different organic matrices beside compost [21], for the first time this method was applied to matrices, such as coconut coir dust and stabilized wood fibre and to mixed growing media
Summary
The valorization of organic waste in ornamental growing media has been recently grown in order to replace peat-based substrates in this sector [1]. The use of by-products, such as green compost, coconut coir dust, and woody fibre, is a widespread promising approach to reduce the use of peat in plant nurseries [2,3,4,5,6,7] For this purpose, both physical and chemical characteristics of the matrices have to be deeply studied to allow the exploitation of new mixtures and a regular and optimal development of healthy plants on alternative peat-free substrates [8,9,10,11,12]. In nurseries there is often no way to perform fertirrigation and correct the water pH, limiting the use of new matrices and substrates that have to be chemically handled For this purpose, standardized methodology is required in absence of these facilities
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