Long-term application of fused magnesium phosphate and calcium silicate change soil chemical properties, C decomposition and N mineralization in a single rice paddy field of Northeastern Japan

Figures & data

Table 1. Details of applications of inorganic fertilizers, organic matter and mineral slags in six treatments

Treatments	Inorganic fertilizer			Organic matter^†		Mineral slag addition
	(kg·ha^−1)			(Mg·ha^−1)		(Mg·ha^−1)
	N	P2O5	K2O	Rice straw	Rice straw compost	FMgP^¶	CaSi^¶
Chemical fertilizer (CF)	80	68	83	-	-	-	-
CF+Mineral slags (CF+)	80	68	83	-	-	0.3	1.5
CF+Rice straw (RS)	80	68	83	6	-	-	-
CF+Rice straw+Mineral slags (RS+)	80	68	83	6	-	0.3	1.5
CF+Compost manure (CM)	80	68	83		10	-	-
CF+Compost manure+Mineral slags (CM+)	80	68	83	-	10	0.3	1.5

^†Water contents of rice straw and rice straw compost were about 10% and 75%, respectively.

^¶FMgP is fused magnesium phosphate and CaSi is calcium silicate.

Figure 1. Long-term effects of mineral slag addition on the changes in pH at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Figure 2. Long-term effects of mineral slag additions on the changes in EC at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Figure 3. Long-term effects of mineral slag additions on the changes in available P at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Figure 4. Long-term effects of mineral slag additions on the changes in soil organic carbon at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Table 2. The best parameters obtained from the 8-week anaerobic incubation experiment at 30°C for measuring the C decomposition potential (C_o) and N mineralization potential (N_o) for the soil samples from different long-term inorganic fertilizer application treatments at 0−25 cm soil depth. The curves were simulated using the first-order reaction model as $D\mathrm{e}\mathrm{c}\mathrm{C}(\mathrm{o}\mathrm{r}Min\mathrm{N})=C_0(\mathrm{o}\mathrm{r}{N}_0)\times \left(1-e^{-K_{c(\mathrm{o}\mathrm{r}\mathrm{n})}t}\right)$

Treatments	C decomposition			N mineralization			Co/No	Kc/Kn
	Co	Kc^†	R^2*	No	Kn^†	R^2*
	(g C kg^−1)	(wk^−1)		(g N kg^−1)	(wk^−1)
CF	0.443	0.442	0.982	0.092	0.398	0.990	4.82	1.11
CF+	0.310	0.509	0.985	0.098	0.365	0.997	3.16	1.39
RS	0.563	0.678	0.974	0.123	0.620	0.988	4.58	1.09
RS+	0.533	0.377	0.995	0.126	0.446	0.978	4.23	0.85
CM	0.493	0.814	0.980	0.111	0.685	0.978	4.44	1.19
CM+	0.466	0.392	0.987	0.127	0.520	0.975	3.67	0.75

^†K_c and K_n are the rate constants for the first-order reaction models.

*R² was the coefficient of determination for each model. All models were fitted significantly at P < 0.01.

Figure 5. Long-term effects of mineral slag additions on the changes in total nitrogen at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Figure 6. Long-term effects of mineral slag additions on the changes in the C/N ratio at the 0–25 cm soil depth (a) and 5-cm soil depth increments (b). Bars are standard deviation (n = 3).

Figure 7. The changes in carbon (C) decomposition (a) and nitrogen (N) mineralization (b) at the 0–25 cm soil depth under anaerobic incubation at 30°C for 8 weeks. Both were simulated by the first-order reaction model as $D\mathrm{e}\mathrm{c}\mathrm{C}(\mathrm{o}\mathrm{r}Min\mathrm{N})=C_0(\mathrm{o}\mathrm{r}{N}_0)\times \left(1-e^{-K_{c(\mathrm{o}\mathrm{r}\mathrm{n})}t}\right)$.