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However, as those volcanic ashes are gradually weathered, much fertilizing-effects appear.
Because adsorbed nitrogens effectively work.
By the way, as an extremely strong fertilizer also withers plants, the concentration of the nitrogen fertilizer must be moderately diluted to obtain best effects.
Therefore, it's often reported that the more distant the interval from a crater gets and the longer the time from the fall of volcanic ash becomes, the higher the fertilizing effect also is.
It's probable that such a spatio-temporal 'distance' contributes to the dilution of the concentration.
Really, it's probable that volcanic ashes work as natural nitrogen fixater to produce nitrogen fertilizers.
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