Phosphorus mineralization from three similar municipal solid waste composts subject to leaching

A laboratory experiment was conducted using three similar, mature, municipa l solid waste (MSW) composts to determine the phosphorus mineralization of each. The treatments consisted of the control (100 % sand), and 50:50 mixtu res of sand and '96, '97, and '98 MSW composts. The date of each MSW compos t corresponds to the year in which it was used in field plots. Each treatme nt was placed in a glass column and replicated four times. The columns were subject to leaching, at room temperature (20+/- 2 degreesC), by adding 100 mi of deionized H2O once a week, for 10 weeks, and then once every two wee ks for another 10 weeks. Inorganic P levels in the leachate were determined colormetrically with a Technicon Autoanalyzer II. The data were statistica lly analyzed with a one-factor ANOVA model at a significance level of 0.05. The levels of H2O extractable P in the '98 MSW leachate were found to be s tatistically higher than in the other three treatments for the first six we eks, with a high of 1640 mug of H2O extractable P. The phosphorous in the ' 96 and '97 MSW compost leachates attained peaks of 327 and 444 mug P, respe ctively; then leveled off to approximately the same amount as the '98 MSW. The control followed the same pattern as the '96 and '97 MSW leachates, but at a lower level. Four of the 20 sampling dates registered water extractab le P levels in the leachate for the control, with a high of 100 mug P. The results suggested differences in the levels of total P in the three MSW com posts, which were found to be 3, 7 and 9 g kg(-1) in the '96,'97, and '98 M SW composts, respectively. This experiment could be expanded to incorporate N and K, and address why the '96 and '97 MSW composts mineralized similarl y but the '98 MSW compost was different.