Effect of ash from forest fires on phosphorus availability, transport, chemical forms, and content in volcanic soils

Abstract

Environmental context. Intensive fertilisation and the availability of phosphorus species (less than 10%) in cultivable soils of volcanic origin are causing the accumulation of P in these soils. Phosphorus is a macronutrient that severely limits good agricultural development, so knowledge of the distribution and the different forms of P present in soils is fundamental for sustainable agricultural practice. This novel study reports the existence of increased available P in all the soils that received a load of plant ash from different tree species. Abstract. The effect associated with the distribution of ash from plantations of native, pine, and eucalyptus forests over five soils of volcanic origin was studied by means of column leaching experiments. The results show a clear increase of pH (up to 4.4 units) and of the soil’s electric conductivity (up to 21 times), whereas total extractable P content increased 3 to 10 times with respect to the control. These effects follow a sequence depending on the origin of the ash (native forest, pine, eucalyptus), concentrated in the 0.0–10.0-cm section from the top of the columns. The observed alkalinity caused an increase of available P (from 21 to 72 times with respect to the control), in addition to decreasing residual P and increasing the extraction efficiency of the method used, discarding a transformation of inorganic P into organic P. Finally, the results show that the addition of ash is a valid and complementary alternative to phosphate fertilisation.