Alleviating soil sickness caused by aerobic monocropping: Responses of aerobic rice to various nitrogen sources

Figures & data

Table 1 Nitrogen sources, N rates, soil, varieties and sampling dates in the four pot experiments

Experiment	Nitrogen source	Nitrogen rate (g pot^−1)	Soil	Variety	Sampling stage
1	Ammonium sulfate, urea, ammonium chloride, ammonium nitrate and potassium nitrate	0.3, 0.6, 0.9 and 1.2	Aerobic soil^†	Apo	Vegetative
2	Ammonium sulfate and urea	0.3, 0.6, 0.9 and 1.2	Aerobic soil^†	Apo	Maturity
3	Ammonium sulfate and urea	1.2	Aerobic soil^† and flooded soil^‡	Apo	Vegetative
4	Ammonium sulfate	1.2	Aerobic soil^†	Apo, IR78877-208-B-1-2 and IR80508-B-57-3-B	Vegetative
^†Soil from a field where aerobic rice has been grown continuously for 11 seasons since 2001 in both dry and wet seasons.
^‡Soil from a field where flooded rice has been grown continuously.

Figure 1  (a) Plant height, (b) stem number, (c) leaf area, (d) above-ground biomass, (e) SPAD value and (f) above-ground N uptake of Apo grown aerobically in soil under five N sources (ammonium sulfate, urea, ammonium chloride, ammonium nitrate and potassium nitrate) at four N rates (N1–N4 = 0.3, 0.6, 0.9 and 1.2 g N pot−1, respectively) and in an untreated control (CK) and oven-heated soil treatment in pot experiment 1. The soil was from an aerobic field where aerobic rice has been grown continuously for 11 seasons. Oven heating of the soil was done at 120°C for 12 h. Error bars represent the standard error.

Figure 2  (a) Panicle number per pot, (b) spikelets per panicle, (c) grain filling, (d) above-ground biomass, (e) harvest index, (f) grain yield, (g) SPAD value and (h) above-ground N uptake of Apo grown aerobically in soil with four rates of ammonium sulfate or urea application (N1–N4 = 0.3, 0.6, 0.9 and 1.2 g N pot−1, respectively) and in an untreated control (CK) and oven-heated soil treatment in pot experiment 2. The soil was from an aerobic field where aerobic rice has been grown continuously for 11 seasons. Oven heating of the soil was done at 120°C for 12 h. Error bars represent the standard error.

Table 2 Plant growth of Apo grown aerobically under the application of ammonium sulfate and urea and oven heating of the soil compared with the untreated control in pot experiment 3

Parameter	Control	Ammonium sulfate^†	Urea^†	Oven^‡
Aerobic soil
Plant height (cm)	45.2 c	77.5 a	58.7 b	80.8 a
Stem number per pot	4.7 d	19.7 b	8.8 c	22.2 a
Leaf area (cm^2 pot^−1)	105 d	951 b	300 c	1,423 a
Above-ground biomass (g pot^−1)	0.96 d	8.51 b	2.70 c	13.98 a
SPAD value	27.7 c	37.4 a	34.4 b	33.7 b
Above-ground N uptake (mg pot^−1)	21 c	266 a	81 b	249 a
Flooded soil
Plant height (cm)	68.8 c	75.7 ab	74.3 b	79.2 a
Stem number per pot	11.5 b	21.3 a	14.3 b	20.7 a
Leaf area (cm^2 pot^−1)	589 b	923 a	690 b	1,106 a
Above-ground biomass (g pot^−1)	5.44 c	8.09 ab	6.28 bc	9.21 a
SPAD value	34.6 b	37.9 a	37.3 a	37.7 a
Above-ground N uptake (mg pot^−1)	121 c	260 a	196 b	262 a
^†The rate of ammonium sulfate and urea was 1.2 g N per pot
^‡Oven heating of the soil was done at 120°C for 12 h. Within a row, means followed by different letters are significantly different at P < 0.05 according to a least significant difference test. The aerobic soil was from a field where aerobic rice has been grown continuously for 11 seasons. The flooded soil was from an adjacent field where flooded rice has been grown continuously.

Figure 3  (a) Plant height, (b) stem number, (c) leaf area, (d) aboveground biomass, (e) SPAD value and (f) above-ground N uptake of three rice varieties grown aerobically under untreated, ammonium-sulfate fertilized soil and oven-heated soil in pot experiment 4. The soil was from an aerobic field where aerobic rice has been grown continuously for 11 seasons. The three varieties were Apo, IR78877-208-B-1-2 and IR80508-B-57-3-B. The rate of ammonium sulfate application was 1.2 g N pot−1. Oven heating of the soil was done at 120°C for 12 h. Error bars represent the standard error.

Table 3 Apparent N recovery rate and root dry weight of Apo grown aerobically under the application of ammonium sulfate and urea in pot experiment 1 (vegetative stage) and 2 (maturity)

Nitrogen rate (g N pot^−1)	Vegetative stage		Maturity
	Ammonium sulfate	Urea	Ammonium sulfate	Urea
Apparent N recovery rate
0.3	0.11 a	0.11 a	0.45 a	0.42 a
0.6	0.22 a	0.11 b	0.43 a	0.41 a
0.9	0.18 a	0.07 b	0.53 a	0.42 b
1.2	0.24 a	0.07 b	0.56 a	0.36 b
Root dry weight (g pot^−1)
0.3	0.92 a	0.95 a	4.1 a	3.5 a
0.6	1.39 a	0.74 b	5.2 b	7.2 a
0.9	1.30 a	0.81 a	6.8 a	6.6 a
1.2	2.00 a	0.76 b	6.5 b	9.8 a
Within a row under each sampling stage, means followed by different letters are significantly different at at P < 0.05 according to a least significant difference test. The aerobic soil was from a field where aerobic rice has been grown continuously for 11 seasons.