Plant husbandry – Mulching
Reexamination Certificate
1999-07-06
2001-11-20
Poon, Peter M. (Department: 3643)
Plant husbandry
Mulching
C047S05810R
Reexamination Certificate
active
06318021
ABSTRACT:
BACKGROUND
This invention relates to a method of treating biomass material such as plant biomass material, and particularly, but not exclusively, to a method of treating such materials with sufficiently large additions of the sesquioxide mineral forming constituents iron and aluminium to form protective coatings on surfaces of the material and to alter the bulk physical and chemical properties of the treated material.
The invention relates particularly to a method of treating plant material in order to protect the material from microbial decomposition.
It is known to use the reduced form of iron, Fe
2+
, and associated salts, in particular iron II sulphate for a number of purposes in agriculture and horticulture, including fertilisers, trace element additives, and slug and moss killers. In a particular use, Iron II sulphate has been used as an additive during the ageing and composting of wood bark, where it is used as an acidity moderator in the same way as other acidity regulating agents such as mineral sulphur.
Application of iron salts has also been used to condition mulches in order to reduce water retention.
The organic complexing properties of iron and aluminium ions in solution have been in common use in water purification treatments and the like to complex, precipitate and sediment coloured and odour producing organic species. Iron and aluminium, together with other more toxic metals such as copper, arsenic and the like are common ingredients of some types of wood preservatives used to protect wood cellulose fibres from fungal attack.
One such known application involves binding these metal ions to detergent chains.
Other wood preservative treatments use powerful iron complexing substances to ensure that fungal growth will be limited due to a shortage of available iron substances.
In a number of other known mulching and compost forming processes other means have been used for conferring protection from microbial decomposition, including resin coatings, colloidal lignite, clay minerals.
Iron III chloride has been used in the field treatment of crop residues. However, such use has proved unsatisfactory for the treatment of mulches and grain media because chloride is phytotoxic to many plant species. In addition, application of oxidised iron has been found to be ineffective at penetrating and reacting with chemical sites and internal surfaces in the treated material due to rapid precipitation.
SUMMARY OF THE INVENTION
Using a reduced iron II salt creates a period of oxygen depletion as dissolved oxygen is consumed by the iron oxidation reaction. This period of oxygen depletion is important, not only for creating a local microenvironment in which iron remains much more soluble for reaction, but also acting as a partial sterilant by depriving aerobic organisms of oxygen.
According to a first aspect of the present invention there is provided a method of treating biomass material to form precipitates of Fe and/or Al oxides and/or hydroxides as a protective coating on the surface of the material.
According to a second aspect of the present invention there is provided a biomass material having been treated by a method according to the first aspect of the present invention.
In natural soils, the persistence of many organic matter constituents (e.g. soil polysaccharide polymer gels and cell wall cellulose structures) is often much longer than for the same materials in laboratory culture. This is attributed to a whole series of physical and chemical protection mechanisms. Physical protection renders material inaccessible to fungal hyphae, bacterial cells and polymer degrading external enzymes that de-polymerise and solubilise the material to release smaller water soluble fractions which can be metabolised. Chemical protection refers to the alteration of polymer surfaces and enzyme cleavage points by complexed and adsorbed substances which inhibit the action of degrading enzymes. Humic substances formed during decomposition in soils and composts and colloidal clay minerals contribute to this physical and chemical protection. However the organic matter in soils is also strongly associated with hydrated and gelatinous hydroxides of iron and aluminium which are also known to be very important contributors to physical and chemical protection. These sesquioxides form naturally through a slow process in all types of soil environments, where release of Fe and Al from mineral weathering, dissolution with pH and changes in the oxidation and reduction state occur.
The present invention provides a process for bringing about the rapid formation of these sesquioxides by treating biomass materials with available and mobile forms of iron and aluminium in aqueous solution.
Most plant materials tend to have a small iron content which results from nutrient uptake during growth. If such plant material content is not intimately mixed into a mineral soil it will not be exposed to conditions where iron complexing will take place.
By means of the present invention iron is added in a mobile and soluble form of Fe
2+
which rapidly promotes the physical and chemical protection mechanisms described above.
Preferably, the method comprises treating plant biomass materials with an addition of effective amount of iron or aluminium sesquioxide forming constituents.
Preferably the sesquioxide comprises a hydrated or gelatinated hydroxide of iron or aluminium.
The invention is particularly appropriate for use with straw from crop plants, chopped wood and bark or compost.
Advantageously, the biomass materials are treated with an aqueous solution of iron ions at a concentration of between 0.1 g and 4.0 g of retained iron per litre of biomass material.
Conveniently the biomass materials are treated with a total of up to 4.0 g of iron or aluminium per litre of biomass.
When applied in a suitable volume of water, this application rate of soluble iron is sufficient to enable distribution, penetration and complexing with substrate chemical binding sites in a biomass material, followed by oxidation of any residual Fe
2+
species into precipitated Fe
3+
oxides or hydroxides. The resultant precipitated coating produced by this process is clearly visible on the surface of biomass materials within a period of one to four hours after treatment.
Plant biomass residue contains variable contents of polyphenolic tannins. Tannins can be more resistant to microbial decomposition than other constituents of the biomass. Tannins are known to bind strongly to proteins and so their ability to bind and inactivate degradative enzymes can confer resistance to breakdown by saprophytic microorganisms. Under moist or water soaking conditions, tannins become mobilised and can leach out of the material. For example, hot water extraction is the most common method for extracting vegetable tannins for other industrial uses such as leather tanning. It is also very widely known that vegetable tannins form strong specific binding complexes with iron, producing dark brown pigmented complexes, and with aluminum ions and that these complexes will precipitate water soluble tannins.
By means of the present invention, by allowing a period of wet or moist soaking in the presence of soluble iron (plus aluminium if added) initial mobilisation of tannins is allowed to take place, following which they come into contact with the iron ions forming the dark brown pigmented precipitates in the biomass material.
By means of the present invention a treatment process is provided whereby the microbial stability and quality of biomass materials is improved for use in substrates for growing plants, horticultural and field mulches, as a peat substitute constituent in composts, as a spray treatment for field crop residues, as a composting additive, as a treatment for other uses for plant biomass in bedding materials and the like, and as a crop residue treatment to bring about a long term increase in the organic matter content of cultivated soils.
Preferably, the biomass material is treated with an aqueous solution of iron prepared by dissolving iron II
Beyer Weaver & Thomas LLP
Gellner Jeffrey L.
Poon Peter M.
The University of Leeds Innovations Ltd.
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