Effects of steel slag applications on CH₄, N₂O and the yields of Indonesian rice fields: a case study during two consecutive rice-growing seasons at two sites

Figures & data

Table 1 Physicochemical characteristics from two different paddy field sites

Soil parameters	Jakenan	Wedarijaksa
Texture (%)
Sand	49	3
Silt	40	45
Clay	12	52
pH
H2O	5.23	6.40
KCl	4.07	5.17
Total organic C (%)	0.51	1.09
Total N (%)	0.05	0.09
CEC (cmolc kg^−1)	3.03	21.66
Available macro and micro elements (mg kg^−1)
Fe	37	13
Mn	8	110
Zn	1.27	0.7
Cu	0.6	1.97
Total silicate (%)	20	24

Figure 1 Meteorological data during the DS in (a) Jakenan, (b) Wedarijaksa and (c) during the RS in both sites.

Table 2 Chemical compositions of steel slag

Parameters	Content
pH (H2O)	10.7
Organic C (%)	2.35
Total N (%)	0.39
P2O5 (%)	2.07
K2O (%)	0.14
Water content (%)	0.78
Total Fe (%)	4.49
Total Si (%)	10.88
Citrate extractable (mg kg^−1)
Fe	9.88
Pb	ud
Cd	ud
As	0.3
Hg	ud

ud = undetected

Table 3 Seasonal CH₄ and N₂O emissions at two different paddy field sites during rice-growing seasons

		CH4		N2O
		DS	RS	DS	RS
Sites	Application of steel slag	kg C ha^−1 season^−1		g N ha^−1 season^−1
Jakenan	Control	135 a	335 a	38.75 a	19.31 bc
	Steel slag 1 Mg ha^−1	149 a	304 a	30.57 a	13.84 c
	Steel slag 2 Mg ha^−1	-	299 a	-	12.78 c
Wedarijaksa	Control	4.99 b	3.10 b	45.99 a	46.03 a
	Steel slag 1 Mg ha^−1	4.96 b	2.71 b	41.43 a	33.70 ab
	Steel slag 2 Mg ha^−1	-	2.52 b	-	28.37 abc
	ANOVA
	Sites	***	***	ns	***
	Application of steel slag	Ns	ns	ns	*
	Sites*steel slag application	Ns	ns	ns	ns

*P < 0.05, **P < 0.01, ***P < 0.001. ns, not significant. Values in each column are means of five replicates. Different letters vertically indicate significant differences between means at P = 0.05 according to Tukey’s HSD-test.

Figure 2 Daily methane fluxes during rice-growing seasons at two different paddy field sites: (a) Jakenan DS, (b) Wedarijaksa DS, (c) Jakenan RS and (d) Wedarijaksa RS. Measurements represent a mean of fifth replicates ± standard error.

Figure 3 Daily nitrous oxide fluxes during rice-growing seasons at two different paddy field sites: (a) Jakenan DS, (b) Wedarijaksa DS, (c) Jakenan RS and (d) Wedarijaksa RS. Measurements represent a mean of fifth replicates ± standard error.

Table 4 The effects of steel slag applications on yield, total biomass and harvest index at two different paddy field sites

Sites	Application of steel slag	DS			RS
		Yield	Total biomass		Yield	Total biomass
		Mg ha^−1		Harvest index	Mg ha^−1		Harvest index
Jakenan	Control	4.36 a	10.3 b	0.42 b	8.79 a	18.6 a	0.48 c
	Steel slag 1 Mg ha-1	4.60 a	11.3 b	0.41 b	9.21 a	18.4 a	0.50 bc
	Steel slag 2 Mg ha-1	-	-	-	9.21 a	17.5 a	0.53 abc
Wedarijaksa	Control	4.58 a	15.4 a	0.30 a	6.90 b	12.9 b	0.54 abc
	Steel slag 1 Mg ha-1	4.09 a	14.7 a	0.28 a	7.23 b	12.0 b	0.60 a
	Steel slag 2 Mg ha-1	-	-	-	6.93 b	12.0 b	0.58 ab
	ANOVA
	Sites	ns	***	***	***	***	***
	Application of steel slag	ns	ns	ns	ns	ns	*
	Interaction	ns	ns	ns	ns	ns	ns

*P < 0.05, **P < 0.01, ***P < 0.001. ns, not significant. Values in each column are means of five replicates. Different letters vertically indicate significant differences between means at P = 0.05 according to Tukey’s HSD-test.

Figure 4 Soil pH during rice-growing seasons at two different paddy field sites: (a) Jakenan DS, (b) Wedarijaksa DS, (c) Jakenan RS and (d) Wedarijaksa RS.

Figure 5 Redox potential during rice-growing seasons at two different paddy field sites: (a) Jakenan RS and (b) Wedarijaksa RS.