Characterization of manures from fish cage farming in Chile.

This study aims to characterize salmonid manures and to determine their potential use in agricultural soils. Sampling was carried out below salmon and trout cages in farms located in lakes and in the sea in the South of Chile during 2002-2003. Manure was analyzed for macronutrients, micronutrients and heavy metals. Results showed a high variability between samples and differences between sea and lake manure. Dry matter contents were low averaging c. 12-15%. Manures showed low OM contents with values <c. 15% and a neutral pH (c. 7.0). Both manures had low total N contents with values of <0.9%, more than 75% of which was in the organic form. Lake manure showed high contents of P (1.56%), Ca (3.89%), Fe (27,948 ppm), Mn (446 ppm), Al (31,789 ppm), As (5.13 ppm), Cd (1.04 ppm), Cr (18.8 ppm), Ni (12.3 ppm), Pb (3.5 ppm) and Zn (393 ppm). Sea manure had high contents of Mg (1.65% ppm), K (0.63%), Na (11.8%) and Cu (89 ppm). Salmonid manure had low nutrients and heavy metal contents and a potential use in agricultural soils, which could reduce the risks of water pollution on water from fish farming.