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ISHS Acta Horticulturae 17: Symposium on Protected Growing of Vegetables


Author:   Dr. B. Werminghausen
DOI:   10.17660/ActaHortic.1971.17.9
A continuing aim of agricultural research is to find materials with good and persistent action in the soil, such as is observed in humus. It is possible to attain this goal by using expanded plastics. Thus, for instance, styrofoam, is suitable for permanent improvement of heavy soils structure and garden mixes and hygromul for amelioration of the water holding capacity of light soils.

Hygromul is an expanded plastic, tolerated by plants. It is obtained in the expanding of a condensation product of urea and formaldehyde. The material has a spongy structure, i.e. mostly open cells and therefore high water holding capacity. Hygromul is a soil amendment agent, which in light soils and substrates holds water and makes possible a good utilization of the water from natural rainfalls and sprinkler irrigation.

The specific gravity of the freshly produced material in blocks ranges from 0.04 to 0.45 and in flakes from 0.011 to 0.013.

The water content of the freshly produced material is about 70% and of the blocky material, following several weeks of storage, about 5% of the weight.

The maximal amount of water retained by freshly produced material is from 1 to 100% of the dry weight and about 50% of the volume.

Analysis results (the values refer to dry material):

N - as total nitrogen - 30.5% Mn - 0.0005%
N - in soluble form  - 0.25% Cu - 0.0034%
P2O5 - 0.57% Zn - 0.0004%
K2O  - 0.0016% Mo - 0.0005%
MgO - 0.004% C   - 32.9%
B      - 0.0001% pH - about 3.0
Fe    - 0.0009%  

This expanded plastic may be considered as an organic substance on the basis of its chemical composition. It may be ashed up to 0.5%.

The high content of nitrogen which is released during the disintegration of the foam in the soil and is available to the plants is of importance. No final evaluation of the durability of the material in the soil can be given as yet. A durability similar to that of peat may be expected.

The foam may be prepared at any time in unlimited amounts and uniform quality. The prerequisites for this was the designing of a foaming equipment. The exigencies concerning the latter were to be of dependable exploitation, simple and not to exceed the size of a truck's loading area.

About 25 m3 of the material are produced in one hour. The expanding may be done in trenches, bales may be formed, or the foam may be sprayed directly in the field. In the last case it is possible to cover

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