Fjölrit RALA - 15.06.2004, Side 20

phosphorus availability. Some plants also have the ability to enhance phosphorus availability
by growing roots to completely encapsulate phosphorus-bearing materials. Silicon is
considered an agronomically essential element for certain plant species (e.g., rice, sugarcane).
Soluble silica concentrations are strongly related to soil mineralogy and the intensity of the
weathering environment. Application of silicate fertilizer not only enhances plant silicon
levels, but may also enhance phosphorus availability by increasing the zero point of charge,
thereby decreasing the phosphate sorption potential. Application of controlled release
fertilizers with nutrient release pattems synchronized to crop nutrient demands can greatly
improve fertilizer-use efficiency for a number of crops grown on Andosols.
Aluminum toxicity is most prevalent in nonallophanic Andosols containing high
concentrations of water soluble and KCl-extractable aluminum derived primarily from 2:1
layer silicates. While these forms of aluminum may be toxic to sensitive crops, they may also
enhance crop productivity by suppressing several soil bome plant pathogens. Subsoil acidity
may limit root development resulting in deep leaching of nutrients and loss of crop
productivity. Surface application of gypsum, phosphogypsum and organic calcium salts may
provide a cost-effective means of ameliorating subsoil acidity.
Based on their degree of development and soil properties, volcanic soils may be considered
among the most productive agricultural soils (generally younger soils) or among the most
infertile agricultural soils (generally nonallophanic Andosols). To maximize the productivity
of volcanic soils, proper management based on an understanding of the unique physical,
chemical, and mineralogical properties of these soils must be practiced.
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