Effectiveness of Extractants for Bioavailable Phosphorus in Tropical Soils Amended with Sewage Sludge

Table 3

Mean extracted phosphorus by Mehlich-I, H₂SO₄, and resin from samples collected at three depths from soils treated with varying rates of sewage sludge, in the long-term experiment ().

Rates	Mehlich-I	H2SO4	Resin
	mg kg^−1
	0–10 cm
0	56.7^c	51.4^c	43.3^b
5	68.8^c	60.6^c	53.0^b
10	125.2^b	102.4^b	104.5^a
20	169.0^a	148.3^a	124.1^a
RL	**	**	**
RQ	ns	ns	ns
	10–20 cm
0	21.7^b	19.4^b	19.2^b
5	24.4^b	21.1^b	22.2^b
10	47.5^ba	40.5^ba	40.8^a
20	77.9^a	65.8^a	53.2^a
RL	**	**	**
RQ	ns	ns	ns
	20–40 cm
0	5.3^b	3.9^b	6.4^b
5	6.0^b	4.5^b	7.6^b
10	8.3^ba	6.1^ba	10.9^ba
20	14.0^a	11.9^a	14.5^a
RL	*	*	**
RQ	ns	ns	ns

(i) RL: linear regression; RQ: quadratic regression; ns: not significant at 5%; ^*significant at 5%; ^**significant at 1%.
(ii) Values with the same letter within a column and same depth are not different (Tukey, ).