( ( ( The ( main advantage ) ) ( of urea ) ) ( ( is ( ( ( its ( low toxicity ) ) , ) ( ( about ( 100,000 ( times less ) ) ) ( than ( that ( of ammonia ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ main) (NN advantage)) (PP (IN of) (NP (NN urea)))) (VP (VBZ is) (NP (NP (PRP$ its) (JJ low) (NN toxicity)) (, ,) (NP (NP (QP (RB about) (CD 100,000) (NNS times) (JJR less))) (PP (IN than) (NP (NP (DT that)) (PP (IN of) (NP (NN ammonia)))))))) (. .)))
The main advantage of urea is its low toxicity, about 100,000 times less than that of ammonia.
(ROOT (S (NP (NP (DT The) (JJ main) (NN advantage)) (PP (IN of) (NP (NN urea)))) (VP (VBZ is) (NP (PRP$ its) (ADJP (RB very) (JJ low)) (NN toxicity))) (. .)))