Agronomic properties of a volcanic ash-derived soil as affected by uncomposted organic materials

A sandy soil from the Vesuvian volcanic area, low in organic matter, was treated in pot experiments with raw farm-yard manure, green horse bean and wheat straw in order to study the effects of organic amendments on physical, chemical and biological properties. Farm-yard manure, rawly composted, caused a significant decrease of bulk density and improved water retention and the content of available phospate and potassium. It also showed the higher conversion co-efficient to stable humus during two years of the incubation period. It depressed the wheat seed germination and cotyledon growth for a one-year incubation period. Horse bean green manure was rapidly mineralized and did not remarkably improve the physical properties of the soil. Furthermore, it produced the lowest humus content and negatively affected seed development for eight months, but remarkably increased nutrient elements' contents (P and K). Wheat straw, added with N (2% urea form), improved humus formation and soil structure compared to horse bean; it increased K and P content and negatively affected seedling development for two months only.