The effects of sewage sludge compost applications on a Mollisol and an Ulti
sol of Puerto Rico were evaluated. Experimental rates were control (0 compo
st), 37, 74, and 148 t/ha/yr, which were to be applied during a three-year
period. In addition, a treatment consisting of a single application of 445
t/ha was included to assess the impact of single massive applications vs. c
ontinuous applications of compost. Results here presented pertain exclusive
ly to the project's first year. The compost was obtained from the sewage sl
udge compost facility of Puerto Rico's Solid Waste Management Authority in
Arecibo. The material was predominantly inorganic and exhibited a high solu
ble salt content, which diminished its quality. Compost additions caused si
gnificant pH increases in both soils. The effects were more noticeable on t
he Ultisol (Corozal clay), where pH increased from 4.55 in the control to 6
.45 with the lowest compost treatment. The electrical conductivity of both
soils increased considerably with compost additions, sometimes appreaching
limits considered detrimental to support crop growth. The organic matter co
ntent of both soils also increased with compost additions. This increase ha
d a positive effect on their water retention capacity. Nitrogen contributio
ns from the compost were minimal. However, significant increases in the lev
els of phosphorus were observed in both soils. Compost additions caused sig
nificant increases in the levels of EDTA extractable metals (i.e., Cu, Zn,
Cd, Cr, Fe). However, elements regulated by the U.S. Environmental Protecti
on Agency (e,g., Cd, Pb, Cr) were added in amounts well below the establish
ed limits, and thus were not a reason for concern.