Organic Extracts for the Treatment of Rock Powder Fertilizers in Biological Agriculture

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Abstract
Four rock dusts of different geological origin (granite, basalt, diabase, volcanic rock) were treated with four organic extracts (amino acid concentrate, brewer's yeast, algae extract of Ascophyllum nodosum, cattle urine) or water as a control in laboratory trials. The experiments were conducted varying the parameters shaking time (0.5 to 3h), extract concentration (1 to 10%) and concentration of rock dust (1.25 to 20%) to demonstrate the degree to which macro- and/or micro-elements could be extracted from various rock dusts. Of the parameters tested, the variation of the concentration and of the kind of rock dust showed the greatest effect on the degree of nutrient extraction when amino acid concentrate or brewer's yeast were used. Ca, Mg and K were extracted to a greater extent from basalt or volcanic rock dust compared to granite or diabase. The greatest extraction value for Mg was obtained using the 5% amino acid concentrate with the addition of 20% basalt dust. Granite dust led to the highest release of Mn with the amino acid concentrate. The relevance of the increase of soluble macro- and micro-elements in the various extracts was evaluated by comparison with available inorganic liquid fertilizers. The nutrient values obtained experimentally in the extracts compared quite favourably with those in the commercially available liquid fertilizer.