ENVIRONMENTAL PHOSPHORUS INDEXES IN MANURE AMENDED SOILS IN THE FRASER BASIN OF BRITISH-COLUMBIA, CANADA

Poultry production in the Fraser Basin of British Columbia, Canada is recognized as one of the primary agricultural income generators for fa rmers. The downside, however, is the large volume of poultry manure th at must be disposed of on a limited land base in environmentally sound ways. There are concerns about the potential translocation of P, as w ell as N and heavy metals, from manure amended soils to surface and gr ound waters. Regulations regarding land disposal of manure should be b ased on knowledge of P behaviour in soils. Soils that had received man ure were sampled. Equilibrium P concentrations at zero sorption (EPC(o )) were determined to assess the possibility of soils to gain or relea se P when they are placed in contact with natural waters. Soils with h igh EPC(o) values have greater possibility to while release P into wat ers than soils with low EPC(o). While Bray-P and oxalate extractable P (P-o) can be used to indicate the available P to plants and natively sorbed P, respectively, they are not related with EPC(o). Neither is t he total P content of the soils. P saturation percentage of soil, whic h is used in the Netherlands as a basis of manure disposal regulation, is in good agreement with EPC(o). This indicates that it is the perce ntage of surface occupied by phosphate rather than the absolute conten ts of various P fractions that determines the movement of P from soil to water. EPC(o) is better than P saturation percentage in concept, bu t the measurement of P saturation percentage is easier than EPC(o). Da ta on soil EPC(o) and P saturation percentage may be helpful in guidin g land disposal of manure to prevent over-applications which may accel erate P transport to surface waters.