Phosphorus release from soils upon exposure to ultra-violet light

Available phosphorus (P) is often low in acid soils either due to its adsor ption or precipitation by iron (Fe) oxides and hydroxides. Ultra-violet(UV) light can induce the release of P from Fe(III)-P compounds though the phot oreduction process. Soils collected from a permanent timothy (Phleum praten se) pasture, subjected to manure applications at different rates and times of the year were irradiated at different UV-B strengths. No significant dif ference was obtained in the release of soluble reactive P (SRP) from soils irradiated at higher strength (45 mw(-1) m(-2)) or lower strength(16 mw(-1) m(-2)) of UV-B. The increase in SRP after UV irradiation, however, was hig hest in soils from unamended subplots followed by subplots amended with man ure in spring and summer. This study showed that sunlight could play a sign ificant role in maintaining a bioavailable P pool in soils. Moreover, the s tudy hypothesized that an application of manure to a timothy pasture in the summer might reduce P loss to runoff and help to utilize native soil P.