Reducing nitrogen pollution while improving tomato production by controlled-release urea application

Figures & data

Figure 1. The accumulative release rate of N from controlled-release urea (CRU) in 25°C water.

Figure 2. Irrigation events and the soil temperature at 15 cm depth in the first season (a) and the second season (b).

Figure 3. Nitrate N concentrations in soil water at a depth of 100 cm in the first season (a) and the second season (b). (The solid arrows represent N top-dressing only for CN treatment at 30, 61 and 83 DAT in the first season, and at 68, 90 and 104 DAT in the second season, respectively).

Table 1. Total N₂O emissions in the seasons of 2012 and 2013.

Treatment	First season (kg/ha)	Second season (kg/ha)	Sum of two seasons (kg/ha)	N2O emissions factor*(%)
CK	2.47 b^§	0.69 c	3.16 b	-
CRN1	2.83 b	1.05 bc	3.88 b	0.08 b
CRN2	2.95 b	1.14 bc	4.09 b	0.08 b
CRN3	3.30 b	1.51 b	4.81 b	0.11 b
CN	5.33 a	2.60 a	7.93 a	0.32 a

^aMeans followed by the same letter in the same list do not differ using the Tukey test (p ≤ 0.05).

^bN₂O emissions factor of each treatment = (N₂O emissions of the treatment – N₂O of CK)/N applied.

Figure 4. N₂O fluxes during the first season (a) and the second season (b) in a greenhouse tomato cropping system in Beijing, northern China.

Table 2. Tomato yields in the seasons of 2012 and 2013.

Treatment	First season (t/ha)	Second season (t/ha)	Sum yield of two seasons (t/ha)
CK	111 a^§	78.6 b	190 b
CRN1	121 a	94.0 ab	216 ab
CRN2	132 a	98.2 a	230 a
CRN3	115 a	85.6 ab	200 ab
CN	113 a	83.3 ab	196 b

^aMeans followed by the same letter in the same list do not differ using the Tukey test (p ≤ 0.05).

Table 3. Nitrogen fertilizer and labor costs as well as income from fruits for the two seasons.

Treatment	N fertilizer cost ($/ha/year)	Labor cost of fertilization^ǂ ($/ha/year)	Income^+ ($/ha/year)	Income increment^++ ($/ha/year)	Economic efficiency^+++
CK	0	150	39,822	0	0
CRN1	326	150	45,300	5,478	11.5
CRN2	476	150	48,300	8,478	13.5
CRN3	627	150	42,000	2,178	2.80
CN	384	420	41,100	1,278	1.59

^a Labor cost of fertilization = labor cost of basal application + labor cost of top-dressing

^b Income = tomato yields × price of tomato.

^c Income increment = income of each treatment – income of CK.

^d Economic efficiency = income increment/(N fertilizer cost + labor cost of fertilization)

Price, CM: 90 $/t; urea, 300 $/t; controlled-release urea, 525 $/t; fresh fruit tomato, 210 $/t; labor cost of basal application: 150 $/ha; labor cost of each top-dressing: 90 $/ha (top-dressing is only conducted at the CN treatment)

Figure 5. Cumulative N release rate from CRUs under field conditions in the two seasons.

Figure 6. Mineral N dynamics in the 0–20 cm soil layer from seedling to harvest in the first season (a) and the second season (b).

Table 4. Calculated apparent N surplus in the greenhouse tomato system in 2012 and 2013 in Beijing, China.

Item	CK	CRN1	CRN2	CRN3	CN
First season kg N/ha
Soil mineral N (0–60 cm) before transplanting	327	327	327	327	327
Organic N	0	134	134	134	134
Chemical N	0	300	450	600	600
N from irrigation water ^d)	6.09	6.09	6.09	6.09	6.09
N uptake by tomato ^b)	221 a ^c)	253 a	262 a	237 a	231 a
Soil mineral N (0–60 cm) after harvest	97.0 d	264 cd	306 bc	468 ab	570 a
N surplus ^a) in the first season  Second season	15.1 b	250 a	349 a	362 a	266 a
Soil mineral N (0–60 cm) before transplanting	97.0 d	264 cd	306 bc	468 ab	570 a
Organic N	0	134	134	134	134
Chemical N	0	300	450	600	600
N from irrigation water	5.55	5.55	5.55	5.55	5.55
N uptake by tomato	177 b	192 ab	213 a	212 ab	211 ab
Soil mineral N (0–60) cm after harvest	94.2 c	276 bc	338 b	478 ab	567 a
N surplus in the second season	−168 c	236 b	345 ab	518 a	532 a
Sum of N surplus of two seasons	−153 c	486 b	694 ab	880 a	798 a

^aN surplus = soil mineral N before transplanting + Organic N from manure + Chemical N from controlled-release urea and CU + N from irrigation water – N uptake by tomato – soil mineral N after harvest

^bPlant dry matter at harvest and N concentrations of plant and fruit are provided in the supplementary table.

^cMeans followed by the same letter in the same row do not differ using the Tukey test (p ≤ 0.05).

^dN from irrigation water (kg N/ha) = irrigation amount (mm) × 3.56 mg N/L/100

Figure 7. Relationships between the N application rate and the average nitrate N concentration in the soil water (a), N₂O emissions (b), and tomato yields (c) under the CK, CRN1, CRN2, and CRN3 treatments based on regression analysis.