Rockdust soil amendment shows promise
Nursery seedlings demonstrate early vigor and fast growth
by Barrie Oldfield
President, The Men of the Trees, Western Australia
Australia's soils are ancient, many millions of years old. Ages of weathering and leaching have left them in an impoverished condition. Australian farmers realize that to grow crops profitably requires continual inputs of soluble fertilizers, especially phosphorus and nitrogen in various forms and essential trace elements. They also know that the cultivation of these soils which lack structure is fraught with land management problems. Despite the greatest care, large tracts of land are lost each year to salt and to wind erosion.
The Men of the Trees, a worldwide voluntary non-governmental organization dedicated to the planting and protection of trees, is active in Western Australia helping rural communities to control wind erosion and salt outbreaks. The establishment of tree seedlings to survive, untended, in a semi-arid environment (annual rainfall in the order of that of the Sahel) is a skill in itself. But having to contend with compacted, acidic, nutrient deficient soils was seen as a problem to be defined and overcome.
In 1989 this voluntary Society began to review work done 100 years ago by the German agronomist Julius Hensel. Hensel showed that if we would mimic the natural soil-forming processes of the millennia, plants would grow with greater vigor and health. Periodic glaciations replenished the soil minerals through the grinding action of the glaciers as they moved over the Earth's crust. Thus the soils of the higher latitudes support a rich agriculture, whilst those of Australia and the warm temperate to tropical world must be regarded as more or less deficient and fragile.
In order to determine how effective remineralization might be, a series of small scatter trials was undertaken. Volunteers, most of them living close to Perth, Western Australia, each undertook to dedicate a four square meter plot to the trial. The quartered plot would contain both treated and control squares, and participants were given a free choice of what plants to grow. In the treated squares a measured amount of finely ground granite dust, equivalent to an application rate of 70 tonnes/hectare, was incorporated into the top 10 cm.
After two seasons of trials the results were collated. Results were varied and somewhat inconclusive, although a "golden thread" started to emerge. Some quantitative work undertaken by two undergraduate student of the School of Biology, Curtin University of Technology, working under the supervision of Dr. J.E.D. Fox, demonstrated significant improvement in both biomass and root development. Overall, there was sufficient evidence to warrant a larger trial at the Society's tree nursery, St. Barbe Grove, at Hazelmore, just outside of Perth.
Setting up the nursery trial
On December 10-11 1990 the trial was set up. Four species of trees were chosen: Eucalyptus gomphocephala, E. angustissima, Casuarina obesa and Acacia saligna. They were seeded into trays, each of which contained 42 Jiffystrip compartments filled with standard nursery potting mix into which finely ground granite dust had been thoroughly mixed. A further two trays were set up with standard potting mix only as a control.
One theory of remineralization holds that soil micro-organisms are revitalized through access to a newly cut face of igneous rock. As both the potting mix and rock dust were sterile materials, it was decided to inoculate half the trays. The inoculant was derived from soil scrapings taken from the A-1 horizon within the feeder root zone of an old Acacia longifolia plus some commercially bagged worm castings.
One third of the trays had rock dust added at the rate of 12 tonnes/hectare, one third at 15/ha, and one third at 20/ha. Of each rock dust application rate, half the trays were inoculated, half left without. The four species of trees were then seeded, with two trays being seeded to each species under each of the six conditions of the trial, giving a total of 48 trays altogether. Finally, the trays were set up on a trestle under normal summer nursery conditions of 50% shade cloth and twice daily watering.
Favorable results became apparent within seven weeks of the start of the trial. First to take the lead was E. gomphocephala. By mid-February 1991 these seedlings were fully double the height of the control, and more abundant in leaf area. The control seedlings were themselves growing at the accepted rate for the seedlings.
This outstanding growth rate attracted widespread interest. Newspaper and television reports appeared. Whilst the publicity was welcome, it did pose some problems in how to answer the many questions about the "chemistry" of the rock dust; and, indeed, if "chemistry" is an adequate description of the function of the dust. One suggestion is that the rock dust, pH 8.6, neutralizes soil acidity and particularly benefits E. gomphocephala, which is known to prefer such conditions.
Then, as the trial proceeded, other tree species began to show extra vigor. Next to take the lead was Acacia saligna. By May 24, 24 weeks into the trial, the best of the trial seedlings were standing 39 cm tall, whilst the control were still at "ground level" making their first phylodes. Casaurina obesa at 24 weeks were 40 percent taller than control, and Eucalyptus angustissima fully double the control height. All plants under rock dust treatment were healthy in appearance. Those that had received the inoculant showed a marginal advantage over those without, but this would need further detailed measurement to fully assess.
Seedlings which are allowed to develop beyond 25 cm tall in the trays at the nursery often exhibit a matting of the roots, indicating an overgrowing in that environment. To test the experimental trees, trays were picked at random, upturned and the tray removed for examination. In no case was root matting a problem. In fact, most seedlings examined at 24 weeks were perfect for planting out, the root tips emerging through the sides of the Jiffy pots into the air space by 1-20 mm.
Broad acre trials to follow
It may be many years before this remineralization trial is concluded, and so it seems appropriate at this time to make a preliminary report in the hope that others may feel encouraged to replicate the trial in both field and laboratory.
Spurred on by the results, The Men of the Trees in Western Australia are taking on 23 hectares of typical wheat-growing country 180 kilometers northeast of Dowerin. Their aim will be to improve and revitalize the soils whilst exploring a range of novel agroforestry systems capable of yielding products of value to the farmer or the farm. All manner of help will be welcomed, advisory, material, practical, or financial.
The Earth Renewal and Restoration Alliance — www.ancientforests.us — www.carbon-negative.us — www.nutrient-dense.info — 2/14/2009