On the responses of carrots (Daucus carota L.) to nitrogen supply

Figures & data

Figure 1. Weather observations at the site of Expt 1314 plotted against DAS carrots: A, cumulative rain; B, cumulative thermal time above a base of 0°C; C, cumulative solar radiation; and D, potential soil water deficit (D_ø). In A–C, the solid lines indicate the observations for the 2013–2014 season and the pecked lines show the average for the previous 10 years. In B, the crosses indicate the days on which N fertiliser was applied.

Figure 2. Weather observations at the site of Expt 1415 plotted against days after sowing carrots (DAS): A, cumulative rain; B, cumulative thermal time above a base of 0°C; C, cumulative solar radiation; and D, potential soil water deficit (D_ø). In A–C, the solid lines indicate the observations for the 2014–2015 season and the pecked lines show the average for the previous 10 years. In D, the crosses indicate the days on which N fertiliser was applied.

Table 1. Soil chemical properties at the experimental sites.

Expt	pH	Soil N (kg N ha^−1)		Olsen P (µg mL^−1)	Exchangeable cations (meq 100 g^−1)
		Mineralisable	Mineral		Ca	K	Mg	Na	CEC
1314	5.63 ± 0.049	145 ± 10	25 ± 3.4	30 ± 2.0	9.9 ± 0.76	1.37 ± 0.062	2.0 ± 0.14	0.10 ± 0.008	19.3 ± 1.29
1415	5.68 ± 0.044	129 ± 31	64 ± 16	30 ± 1.7	10.9 ± 0.48	1.06 ± 0.055	1.8 ± 0.11	0.14 ± 0.017	18.0 ± 0.73

Notes: Values are quoted as means ± standard deviation. Sampling depth was 0–15 cm for all observations except the mineral nitrogen (N), which represents the total extracted from 0 to 60 cm depth in a solution of 2 mol L⁻¹ KCl. Mineralisable N was measured following anaerobic incubation at 40°C for 7 days (Keeney and Bremner 1966). CEC: cation exchange capacity measured at pH 7.0.

Figure 3. Carrot plant populations through the season for the 1314 and 1415 experiments. The control (N0) treatment means are shown ± the mean standard error (MSE) from the analysis of variance for that sampling occasion. For any individual occasion, the 95% confidence limit for comparisons between any two means is twice the MSE. Nitrogen fertiliser treatments are described in the text.

Table 2. Least squares regressions of biomass and storage root dry matter yields (t ha⁻¹) on plant population (m⁻²) for carrots in the 1314 and 1415 experiments.

			Total crop dry matter yield (t ha^−1) vs. plant population (m^−2)							Storage root dry yield (t ha^−1) vs. plant population (m^−2)
			Intercept = a			Slope = b				Intercept = a			Slope = b
Expt	DAS	n	Value	SE	P	Value	SE	P	R^2	Value	SE	P	Value	SE	P	R^2
1314	24	15	−0.002	0.0012	0.14	0.0002	0.00003	<0.001	0.74	0	0.0001	0.96	0	0	<0.01	0.55
	37	15	0.01	0.038	0.71	0.0024	0.00096	0.03	0.32	0.002	0.0054	0.65	0.0003	0.00014	0.08	0.22
	57	15	0	0.3	0.91	0.058	0.0082	<0.001	0.79	0	0.12	0.86	0.02	0.0032	<0.001	0.75
	73	15	1.4	0.81	0.11	0.09	0.021	<0.01	0.56	0.9	0.36	0.02	0.04	0.0093	<0.001	0.59
	86	15	0	1.9	0.91	0.20	0.045	<0.001	0.60	1	1.1	0.38	0.1	0.025	<0.01	0.55
	100	15	1	2.6	0.6	0.25	0.065	<0.01	0.53	2	1.6	0.34	0.15	0.04	<0.01	0.51
	114	15	3	2.5	0.27	0.23	0.061	<0.01	0.52	3	1.8	0.18	0.14	0.044	<0.01	0.43
	128	15	6	4.3	0.16	0.2	0.11	0.05	0.27	5	2.7	0.10	0.17	0.066	0.03	0.33
	143	15	7	6.3	0.28	0.3	0.17	0.14	0.16	5	4.5	0.25	0.2	0.12	0.12	0.17
	156	15	6	4.7	0.2	0.3	0.12	0.03	0.32	6	3.4	0.12	0.22	0.09	0.03	0.32
	170	15	12	6.4	0.09	0.2	0.16	0.35	0.07	9	4.8	0.07	0.1	0.12	0.35	0.07
1415	44	20	0	0.025	0.89	0.0016	0.00048	<0.01	0.38	0	0.0042	0.92	0.00024	0.00008	<0.01	0.32
	64	20	0.7	0.35	0.07	0.029	0.0071	<0.001	0.49	0.3	0.14	0.07	0.009	0.0028	<0.01	0.37
	78	20	3.9	0.72	<0.001	0.03	0.013	0.02	0.26	1.9	0.32	<0.001	0.014	0.0057	0.02	0.27
	92	20	7	1.1	<0.001	0.05	0.021	0.04	0.22	3.2	0.72	<0.001	0.04	0.014	0.01	0.29
	106	20	8	1	<0.001	0.09	0.018	<0.001	0.59	5.1	0.69	<0.001	0.06	0.012	<0.001	0.54
	120	20	8	1.8	<0.001	0.12	0.035	<0.01	0.4	6	1.4	<0.001	0.07	0.028	0.02	0.29
	136	20	10	2	<0.001	0.13	0.037	<0.01	0.42	7	1.6	<0.001	0.09	0.03	<0.01	0.32
	148	20	16	2.5	<0.001	0.1	0.048	0.06	0.18	12	1.9	<0.001	0.07	0.037	0.07	0.17
	162	20	14	3.2	<0.001	0.16	0.065	0.03	0.24	10	2.3	<0.001	0.12	0.047	0.02	0.27
	176	20	14	3.4	<0.001	0.18	0.061	<0.01	0.32	11	2.6	<0.001	0.13	0.045	0.01	0.31
	203	20	15	2.1	<0.001	0.18	0.039	<0.001	0.53	12	1.6	<0.001	0.14	0.029	<0.001	0.55

Notes: Coefficients are given for the generic equation y = a + bx. P designates the probability that the intercept or slope terms are different from zero. DAS: days after sowing.

Table 3. Effects of nitrogen (N) fertiliser treatments on N concentrations (% dry matter) in process carrots at 156 days after sowing (Expt 1314) and 203 days after sowing (Expt 1415).

Variable	Treatment means					MSE	F	P values
	N0	N0.5	N1	N1.5	N2			Treatment effects	Population covariate
Expt 1314
Green leaf concentration	1.2	1.6	1.4	1.5	1.7	0.21	1.99	0.20	0.74
Storage root concentration	1.16	1.29	1.27	1.46	1.47	0.086	9.54	<0.01	0.47
Whole-plant concentration	0.8	1.2	1.1	1.5	1.4	0.8	6.73	0.02	0.04
Net uptake (kg ha^−1)	220	280	270	340	330	36	9.43	<0.01	0.12
Expt 1415
Green leaf concentration	1.3	1.4	1.5	1.8	1.7	0.30	4.16	0.03	0.88
Storage root concentration	1.0	1.1	1.3	1.3	1.4	0.16	8.96	<0.01	0.26
Whole-plant concentration	1.0	1.3	1.4	1.5	1.4	0.19	5.02	0.02	<0.001
Net uptake (kg ha^−1)	220	280	320	330	320	60	4.83	0.02	0.08

Notes: The analyses of variance were carried out using plant population (m⁻²) as a covariate. Treatments are described in the text.

Figure 4. Influence of nitrogen (N) supply on N concentration in green leaves (hollow symbols) and storage roots (solid symbols) of carrots: A, Expt 1314 at 156 days after sowing (DAS); and B, Expt 1145 at 203 DAS.

Figure 5. Influence on nitrogen supply (N_supply) on the net uptake of N by carrot crops in Expt 1314 (at 156 days after sowing (DAS), hollow symbols), and Expt 1145 (at 203 DAS, solid symbols). The plotted line is that for uptake to equal supply.

Figure 6. Carrot crop growth through Expt 1314: A, Green leaf area index (L_G); B, Green shoot dry yield; C, Storage root dry yield; and D, biomass yield. DAS = days after sowing. On each graph the crosses indicate times when nitrogen fertiliser was applied. Treatment means for the control (N0) treatment are plotted ± the mean standard error (MSE) from the analysis of variance for that day (using plant population and replicate block as covariates). The 95% confidence interval for separation between treatment means is approximately 2×MSE.

Table 4. Effects of nitrogen (N) fertiliser treatments on the fraction of incident light intercepted by carrot crops in Expt 1314 and Expt 1415.

		Treatment means
Expt	DAS	N0	N0.5	N1	N1.5	N2	MSE	F	Treatment effects P
1314	35	0.07	0.11	0.08	0.04	0.08	0.029	1.03	0.45
	85	0.91	0.96	0.94	0.95	0.96	0.012	4.12	0.04
	98	0.89	0.92	0.92	0.93	0.92	0.022	0.61	0.67
	113	0.86	0.91	0.91	0.93	0.93	0.019	3.04	0.09
	127	0.89	0.94	0.93	0.95	0.95	0.019	2.45	0.13
	140	0.87	0.92	0.93	0.96	0.94	0.024	2.79	0.10
	169	0.918	0.954	0.961	0.959	0.958	0.0095	5.06	0.03
1415	67	0.87	0.82	0.91	0.83	0.86	0.026	2.89	0.07
	81	0.97	0.95	0.94	0.96	0.96	0.011	1.31	0.32
	98	0.96	0.95	0.95	0.97	0.95	0.017	0.43	0.79
	107	0.96	0.95	0.95	0.96	0.96	0.011	0.48	0.75
	130	0.974	0.979	0.976	0.981	0.976	0.0081	0.16	0.96
	150	0.976	0.983	0.99	0.99	0.993	0.0057	2.26	0.12
	165	0.986	0.991	0.99	0.993	0.996	0.0039	1.66	0.22
	179	0.99	0.995	0.995	0.994	0.994	0.0026	1.00	0.46
	189	0.973	0.985	0.989	0.977	0.979	0.0076	1.14	0.38
	205	0.984	0.988	0.989	0.99	0.984	0.0046	0.55	0.70

Notes: The analyses of variance were not carried out using plant population (p, m⁻²) as a covariate, because p was not measured on the same days as light interception, and the latter was measured non-destructively on up to four separate locations in each plot. DAS: days after sowing. Treatments are described in the text.

Table 5. Analysis of variance for fresh storage root yields (t ha⁻¹) of carrots in Expt 1314 and 1415.

		Treatment means							P values
Expt	DAS	N0	N0.5	N1	N1.5	N2	MSE	F	Treatment effects	Population covariate
1314	24	0.0036	0.0036	0.0041	0.0039	0.0047	0.00086	1.34	0.35	0.08
	37	0.13	0.11	0.14	0.14	0.14	0.037	0.32	0.86	0.16
	57	6	7	7	7	7	1.1	1.08	0.43	<0.01
	73	19	23	22	22	23	1.9	2.28	0.16	<0.01
	86	41	45	42	42	49	4.2	4.12	0.05	<0.01
	100	67	71	62	69	76	8.7	1.92	0.21	0.01
	114	70	90	80	90	90	11	6.41	0.02	0.07
	128	80	100	100	110	100	12	3.62	0.07	0.07
	143	90	110	120	120	120	17	5.24	0.03	0.50
	156	110	130	130	150	140	15	6.41	0.02	0.17
	170	130	140	140	160	160	24	0.78	0.57	0.21
1415	44	0.09	0.06	0.07	0.08	0.08	0.024	1.27	0.34	0.02
	64	5.4	4.5	5.1	4.7	5.7	0.86	1.81	0.20	0.04
	78	20	17	19	19	21	2.1	1.87	0.19	0.41
	92	36	36	35	40	39	3.3	1.52	0.26	0.33
	106	52	51	52	52	51	3.9	2.53	0.10	<0.001
	120	66	68	61	73	71	6.2	3.24	0.05	<0.001
	136	100	100	100	100	90	13	0.95	0.47	0.03
	148	110	110	110	120	110	15	0.54	0.71	0.15
	162	120	120	110	120	120	12	0.17	0.95	0.01
	176	120	130	130	120	130	11	4.98	0.02	0.01
	203	130	140	140	140	140	13	1.05	0.42	<0.01

Notes: Replicate block and plant population (p, m⁻²) were used as covariates, but only p was ever significant at P < 0.05. DAS: days after sowing. Treatments are described in the text.

Table 6. Analysis of variance for the effects of nitrogen (N) fertiliser treatments on growth and yield of carrots where data have been pooled for all observation dates.

Expt	Variable	Treatment means					MSE	F	P values
		N0	N0.5	N1	N1.5	N2			Main treatment	Population covariate
1314	Green leaf area index	3.1	3.7	3.7	4.1	4.1	0.16	10.03	<0.001	<0.001
	Total leaf area index	3.2	3.8	3.8	4.3	4.3	0.17	10.13	<0.001	<0.001
	Leaf specific area (cm^2 g^−1)	104	103	104	104	104	4	0.02	1	0.17
	Green shoot dry yield (t ha^−1)	2.8	3.4	3.4	3.7	3.8	0.12	15.45	<0.001	<0.001
	Dead shoot dry yield (t ha^−1)	0.04	0.04	0.06	0.13	0.09	0.026	2.38	0.05	0.25
	Storage root dry yield (t ha^−1)	5.5	6.7	6.4	7.1	7	0.32	6.02	<0.001	<0.001
	Total dry matter yield (t ha^−1)	8.4	10.2	9.9	11	10.9	0.42	9.61	<0.001	<0.001
	Harvest index	0.665	0.645	0.643	0.632	0.63	0.0082	3.76	<0.01	<0.001
	Storage root fresh yield (t ha^−1)	44	55	53	60	58	2.5	9.59	<0.001	<0.001
	Fraction light intercepted	0.92	0.96	0.95	0.96	0.97	0.011	3.31	0.01
1415	Green leaf area index	4	4.22	4.23	4.49	4.29	0.088	3.90	<0.01	<0.001
	Total leaf area index	4.1	4.28	4.34	4.59	4.44	0.095	4.12	<0.01	<0.001
	Leaf specific area (cm^2 g^−1)	91	89	91	91	91	1.4	0.75	0.56	0.04
	Green shoot dry yield (t ha^−1)	4.39	4.71	4.63	4.89	4.67	0.094	2.99	0.02	<0.001
	Dead shoot dry yield (t ha^−1)	0.1	0.06	0.11	0.09	0.15	0.028	1.88	0.11	<0.01
	Storage root dry yield (t ha^−1)	9.8	10.3	9.9	10.3	10.2	0.29	0.61	0.66	<0.001
	Total dry matter yield (t ha^−1)	14.2	15.1	14.6	15.3	15.1	0.34	1.18	0.32	<0.001
	Harvest index	0.684	0.678	0.674	0.673	0.681	0.0049	1.07	0.37	<0.001
	Storage root fresh yield (t ha^−1)	74	79	77	79	78	2.1	0.67	0.61	<0.001
	Fraction light intercepted	0.986	0.981	0.99	0.987	0.988	0.0048	0.64	0.64

Notes: DAS: days after sowing. Treatments are described in the text. Plant population, DAS, DAS² and replicate block number were used as covariates, except for the fraction of intercepted light, where plant population was not available for use as a covariate. For all variables, P was <0.001 for the DAS covariate and >0.05 for the replicate block number covariate and so these values are not reproduced below. For all rows of the table the standard errors for each treatment mean were very close to the mean standard error (MSE), so the 95% confidence interval for a comparison between any two means is very close to twice the MSE. Observations were continued for longer in Expt 1415 than in Expt 1314, which largely explains the larger dry yields means below for Expt 1415.

Figure 7. Carrot crop growth through Expt 1415; A, Green leaf area index (L_G); B, Green shoot dry yield; C, Storage root dry yield; and D, biomass yield. DAS = days after sowing. On each graph the crosses indicate times when nitrogen fertiliser was applied. Treatment means for the control (N0) treatment are plotted ± the mean standard error (MSE) from the analysis of variance for that day (using plant population and replicate block as covariates). The 95% confidence interval for separation between treatment means is approximately 2×MSE.

Table 7. Least squares regressions of total dry matter (biomass) yield and storage root dry yield on nitrogen supply (N_supply, kg ha⁻¹) and plant population (p, m⁻²) for carrots in Expt 1314.

			a			b1 (Nsupply effect)			b2 (p effect)
	DAS	n	Value	SE	P	Value	SE	P	Value	SE	P	R^2
Total dry matter yield (t ha^−1)
	37	15	0	0.13	0.79	−0.0001	0.00068	0.87	0.002	0.001	0.04	0.2
	57	15	−1.2	0.72	0.11	0.005	0.0029	0.09	0.061	0.0078	<0.01	0.81
	73	15	−1	1.2	0.36	0.012	0.0048	0.03	0.09	0.018	<0.01	0.66
	86	15	−2	2.4	0.41	0.011	0.0076	0.19	0.2	0.043	<0.01	0.60
	100	15	−1	3	0.67	0.012	0.0076	0.13	0.24	0.061	<0.01	0.55
	114	15	0	3	0.87	0.013	0.0094	0.18	0.22	0.06	<0.01	0.53
	128	15	1	4.3	0.81	0.03	0.013	0.03	0.19	0.093	0.07	0.43
	143	15	0	5.3	1.00	0.04	0.013	<0.01	0.2	0.13	0.20	0.47
	156	15	2	4.6	0.75	0.03	0.011	0.04	0.3	0.11	0.03	0.45
	170	15	0	8.2	0.99	0.03	0.013	0.07	0.3	0.16	0.10	0.19
Storage root dry yield (t ha^−1)
	37	15	0	0.018	0.81	−0.00001	0.000096	0.91	0.0003	0.00014	0.09	0.09
	57	15	−0.3	0.3	0.39	0.001	0.0012	0.39	0.021	0.0033	<0.01	0.73
	73	15	0.2	0.61	0.77	0.003	0.0024	0.17	0.041	0.009	<0.01	0.60
	86	15	0	1.4	0.91	0.005	0.0044	0.26	0.10	0.025	<0.01	0.53
	100	15	1	2	0.54	0.001	0.0051	0.79	0.15	0.041	<0.01	0.43
	114	15	3	2.3	0.29	0	0.0072	0.96	0.14	0.046	0.01	0.34
	128	15	2	2.9	0.50	0.016	0.0085	0.09	0.14	0.062	0.04	0.39
	143	15	1	3.9	0.90	0.029	0.0094	0.01	0.14	0.098	0.17	0.45
	156	15	2	3.4	0.51	0.018	0.008	0.04	0.19	0.08	0.04	0.44
	170	15	1	6.4	0.83	0.018	0.0099	0.10	0.2	0.12	0.12	0.14

Notes: DAS: days after sowing. Coefficients are given for the generic equation y = a + b₁N_supply + b₂p. P designates the probability that the a, b₁ or b₂ terms are not different from zero. Note that the R² values are generally larger for the regressions of scaled biomass yield. Results are given only for times after the first application of N fertiliser.

Table 8. Least squares regressions of total dry matter (biomass) yield and storage root dry yield on nitrogen supply (N_supply, kg ha⁻¹) and plant population (p, m⁻²) for carrots in Expt 1415.

			a			b1 (Nsupply effect)			b2 (p effect)
	DAS	N	Value	SE	P	Value	SE	P	Value	SE	P	R^2
Total dry matter yield (t ha^−1)
	64	20	−0.2	0.76	0.8	0.004	0.0029	0.22	0.032	0.0072	<0.01	0.48
	78	20	4	1.5	0.02	0	0.0056	0.98	0.03	0.013	0.03	0.17
	92	20	2	1.4	0.1	0.015	0.0041	<0.01	0.06	0.017	<0.01	0.51
	106	20	5	2.1	0.02	0.008	0.0061	0.23	0.10	0.019	<0.01	0.58
	120	20	3	2.5	0.2	0.016	0.0064	0.02	0.14	0.031	<0.01	0.52
	136	20	12	3.3	<0.01	−0.007	0.008	0.41	0.12	0.039	<0.01	0.38
	148	20	15	3.6	<0.01	0.003	0.0069	0.68	0.10	0.051	0.06	0.09
	162	20	12	4.6	0.02	0.006	0.0097	0.53	0.17	0.068	0.03	0.17
	176	20	10	4.3	0.03	0.014	0.0094	0.15	0.18	0.058	<0.01	0.33
	203	20	15	2.9	<0.01	0.002	0.0065	0.76	0.18	0.04	<0.01	0.47
Storage root dry yield (t ha^−1)
	64	20	−0.1	0.3	0.8	0.001	0.0012	0.22	0.01	0.0029	<0.01	0.36
	78	20	1.7	0.68	0.02	0.001	0.0025	0.79	0.015	0.006	0.02	0.18
	92	20	0.3	0.84	0.69	0.01	0.0024	<0.01	0.046	0.01	<0.01	0.62
	106	20	3	1.4	0.03	0.006	0.0041	0.18	0.06	0.013	<0.01	0.54
	120	20	2	2	0.27	0.012	0.0051	0.03	0.08	0.025	<0.01	0.40
	136	20	9	2.6	<0.01	−0.007	0.0064	0.32	0.08	0.031	0.02	0.28
	148	20	12	2.8	<0.01	0.001	0.0054	0.85	0.07	0.039	0.08	0.07
	162	20	9	3.3	0.02	0.004	0.0069	0.61	0.13	0.049	0.02	0.20
	176	20	9	3.3	0.01	0.009	0.0072	0.25	0.13	0.045	<0.01	0.29
	203	20	13	2.2	<0.01	−0.002	0.0049	0.76	0.14	0.03	<0.01	0.50

Notes: DAS: days after sowing. Coefficients are given for the generic equation y = a + b₁N_supply + b₂p. P designates the probability that the a, b₁ or b₂ terms are not different from zero. Note that the R² values are generally larger for the regressions of scaled biomass yield. Regression results are given only for times after the first application of N fertiliser.

Keeney DR, Bremner JM. 1966. Comparison and evaluation of laboratory methods of obtaining an index of soil nitrogen availability. Agronomy Journal. 58:498–503. doi: 10.2134/agronj1966.00021962005800050013x

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