Fresh and Composted Paper Sludges Sustain Soil Productivity

Table 4

Residual effects of applications of fresh and composted paper sludge, and N fertilizer on soil bulk density, nitrogen and carbon contents, C/N ratio, and C (Mg ha^-1) at 10–20-cm soil layer in 2004.

Treatments	Bulk density	Total N	C	C/N	C
	g cm^-3	g kg^-1	g kg^-1		Mg ha^-1
Frequency (single application)
Control	1.49	1.36	16.7	12	41.80
N fertilizer (160 kg N ha^-1)	1.52	1.27	14.9	12	38.60
FDS	1.45	1.53	20.4	13	50.23
CDS	1.48	1.50	19.0	13	47.56
FDS + 120 kg N ha^-1	1.50	1.47	20.0	13	50.97
CDS + 120 kg N ha^-1	1.47	1.58	20.6	13	50.75
Frequency (triple application)
Control	1.53	1.34	16.3	12	42.35
N fertilizer (160 kg N ha^-1)	1.47	1.31	16.3	12	40.80
FDS	1.41	1.57	22.6	14	54.02
CDS	1.46	1.44	19.1	13	47.50
FDS + 120 kg N ha^-1	1.43	1.49	20.6	14	49.91
CDS + 120 kg N ha^-1	1.43	1.57	21.9	14	52.75
ANOVA F values
Treatments	2.62	10.52^∗∗	24.86^∗∗	20.00^∗∗	20.68^∗∗
Frequency	4.14	0.00	4.69^∗	16.51^∗∗	1.72
Treatments × Frequency	1.04	0.32	0.86	1.23	0.58
Contrasts
(1) Control versus others	5.52^∗	10.55^∗∗	31.56^∗∗	31.71^∗∗	24.21^∗∗
(2) N fert. versus FDS and CDS	4.94^∗	35.44^∗∗	78.08^∗∗	52.00^∗∗	69.44^∗∗
(3) FDS versus CDS	0.28	0.09	2.14	12.39^∗∗	2.02
(4) FDS^‡ versus FDSN^§	1.68	1.92	2.88	0.70	1.06
(5) CDS^{ versus CDSN^#	0.67	4.61^∗	9.64^∗∗	3.20	6.68^∗

∗. ∗∗ =.05 and  .01 probability levels of statistically significant difference, respectively.
^‡FDS, ^§FDSN: fresh paper sludges alone or with N fertilizer, respectively.
^{CDS, ^#CDSN: composted paper sludges alone or with N fertilizer, respectively.