Modelling nitrogen transport and transformation in a transplanted rice field experiment with reduced irrigation

Figures & data

Table 1. Selected physical and chemical properties of the tested soil in the Taihu Lake Basin of Eastern China.

Depth (cm)	Distribution of soil particle (%)		BD (g cm^−3)	OM (%)	TN (mg kg^−1)	(mg kg^−1)	(mg kg^−1)	pH (H2O)
	Silt (0.002–0.05 mm)	Clay (< 0.002 mm)
0–20	73.70	19.29	1.42	0.51	1543	4.6	6.2	6.65
20–40	81.01	18.97	1.56	0.54	621	3.1	5.8	6.85
40–60	72.83	8.64	1.51	0.37	344	2.4	4.7	6.85
60–80	81.64	3.91	1.43	0.35	313	1.2	5.1	6.80
80–100	81.59	4.16	1.43	0.33	243	1.3	4.3	6.80
100–120	80.30	8.38	1.43	0.33	224	1.4	3.4	6.85

Note: BD–bulk density, OM–organic matter, TN–total soil nitrogen.

Table 2. Agricultural activities for the transplanted rice under multiple shallow irrigation in the Taihu Lake Basin of China.

Date	Agricultural activities
2008.5.19, 2009.5.17	Raise rice nursery (400 kg seeds ha^−1, 75 kg N ha^−1)
2008.6.19, 2009.6.14	Basal fertiliser (88 kg N ha^−1); Plowed by machine (about 10 cm top soil)
2008.6.21, 2009.6.16	Transplant (1.05 × 10^6 rice seedlings ha^−1 and 2.5 × 10^5 hole ha^−1)
2008.7.12, 2009.7.10	Topdressing fertiliser (TF1, 66 kg N ha^−1)
2008.7.20–30, 2009.7.14–20	Soil drying stage
2008.8.5, 2009.8.5	Topdressing fertiliser (TF2, 66 kg N ha^−1)
2008.10.25, 2009.10.20	Harvested

Table 3. Nitrogen transformation parameters in soil used in the Hydrus-1D simulations in Lake Taihu Basin, China.

Soil layer (cm)	Kmi(day^−1)	Kd (L mg^−1)	Kn(day^−1)	Kdn(day^−1)	Kh(day^−1)
0–20	0.0045	1.8	0.26	0.04	0.74
20–40	0.0045	1.5	0.23	0.06
40–60	–	1.2	0.12	0.05
60–80	–	1.0	0.05	0.02
80–100	–	1.0	0.02	0.01
100–120	–	1.0	0.02	0.01

Note: K_mi – the comprehensive production rate of representing mineralisation/immobilisation; K_d – the distribution coefficient for ; K_n – the nitrification rate; K_dn – the denitrification rate; and K_h – the urea hydrolysis rate.

Table 4. Statistical indices (RMSE, E, d, and n) for assessing nitrogen (N) transport and transformation parameters using in Hydrus-1D simulations in the experimental transplanted rice field during the 2008 and 2009 seasons.

Items		RMSE	E	d	n
AV rate		0.026/0.042* kg ha^−1 day^−1	0.923/0.863	0.979/0.960	46/50
N concentration	in flood water	0.123/0.399 mg L^−1	0.974/0.933	0.993/0.981	39/49
	at 20 cm depth	0.084/0.107 mg L^−1	0.978/0.979	0.994/0.994	38/38
	at 40 cm depth	0.053/0.066 mg L^−1	0.938/0.906	0.984/0.975	38/38
	at 60 cm depth	0.032/0.040 mg L^−1	0.904/0.800	0.968/0.865	38/38
	at 80 cm depth	0.025/0.038 mg L^−1	0.696/−0.372	0.858/0.654	38/38
N flux	at 60 cm depth	0.094/0.141 kg ha^−1	0.976/0.912	0.993/0.937	18/18
Total N	in plant	0.873/0.892 kg ha^−1	0.994/0.995	0.999/0.999	9/9

Note: RMSE – the root mean square error, E – the Nash–Sutcliffe modelling efficiency, d – the index of agreement, n – the number of observed data, AV – ammonia volatilisation, * – the former and later data are for the 2008 and 2009 seasons, respectively.

Figure 1. Simulated (Sim.) and observed (Obs.) and concentrations in floodwater during the 2008 (a) and 2009 (b) seasons. P+I: precipitation and irrigation; BF: basal fertiliser; TF₁ and TF₂: topdressing fertiliser; the arrows at the top indicate fertiliser applications; DAB: days after basal fertiliser application.

Figure 2. Simulated (Sim) and observed (Obs) ammonia volatilisation (AV) fluxes and simulated cumulative (Cum) AV fluxes during the 2008 (a) and 2009 (b) seasons. BF: basal fertiliser; TF₁ and TF₂: topdressing fertiliser; the arrows at the top indicate fertiliser applications; DAB: days after basal fertiliser application.

Figure 3. Simulated cumulative (Cum.) nitrogen uptake (,, and total) and observed (Obs.) total nitrogen uptake during the 2008 (a) and 2009 (b) seasons. DAB: days after basal fertiliser application.

Figure 4. Comparison of simulated (Sim.) and observed (Obs.) (a, c) and (b, d) concentrations at 20, 40, 60, and 80 cm depths during the 2008 (a, b) and 2009 (c, d) seasons. BF: basal fertiliser; TF₁ and TF₂: topdressing fertiliser; the arrows at the top indicate fertiliser applications; DAB: days after basal fertiliser application.

Figure 5. Simulated (Sim) cumulative nitrogen fluxes at 0, 20, 40, and 60 cm depths below the soil surface and observed (Obs) cumulative (Cum.) nitrogen fluxes at the 60 cm depth during the 2008 (a) and 2009 (b) seasons. DAB: days after basal fertiliser application.

Table 5. Simulated nitrification and denitrification amounts (kg ha⁻¹) in soil in the multiple shallow irrigated transplanted rice field during the 2008 and 2009 seasons.

Soil depth (cm)	2008 season		2009 season
	Nitrification	Denitrification	Nitrification	Denitrification
0–20	112.6	47.2	118.0	44.3
20–40	62.7	58.3	68.4	59.1
40–60	10.6	24.1	14.7	29.4
60–80	0.7	5.9	1.5	9.4
80–100	0.3	1.7	0.6	3.6
100–120	0.2	1.0	0.4	2.5
Total	187.1	138.2	203.5	148.3

Table 6. Simulated components of nitrogen balance (kg ha⁻¹) in a 60 cm soil profile of the multiple shallow irrigated transplanted rice (TPR) and direct-seeded rice (DSR) fields during the 2008 and 2009 seasons.

Season	F	M	AV	D	SR	P	CU	SS	δ
2008-TPR	220	94.2	−50.6	−129.6	0	−8.9	−118.5	−14.3	2.3
2009-TPR	220	119.9	−53.4	−132.8	−4.1	−20.9	−116.8	−13.8	−1.9
2008-DSR	220	145.5	−63.4	−136.1	−10.3	−25.3	−114.8	−17.6	−2.0
2009-DSR	220	147.8	−58.6	−138.0	−17.0	−24.7	−112.1	−16.9	−0.5

Note: F – fertiliser, M – mineralisation, AV – ammonia volatilisation, D – denitrification, SR – surface runoff, P – percolation, CU – crop uptake, SS – change in soil storage, δ – total nitrogen balance error.