Rapid Diagnosis of the Nitrogen Status of the Wild Lowbush Blueberry

Figures & data

Figure 1. Effect of nitrogen (N) fertilizer on leaf N concentration during the growing season (average for sites). The dotted lines indicate the minimum and maximum values of optimal concentrations (Lafond, 2009). L: linear effect of N rates for a given date: ***, significant at P < .0001.

Table 1. Analysis of variance (probability value) for the effects of sites and rates of nitrogen (N), phosphorus (P) and potassium (K) on the leaf N concentrations, and on the values of SPAD and Dualex₃ according to the different sampling times.

	Early July			End of July			Mid-August			End of August
	N	SPAD	Dualex	N	SPAD	Dualex	N	SPAD	Dualex	N	SPAD	Dualex
Site	0.0002	0.0038	0.0001	0.0001	0.0001	0.0001	0.0001	0.0001	0.0001	0.0001	0.0006	0.0001
N rate	0.0001	0.0014	0.0001	0.0001	0.0001	0.0240	0.0001	0.0001	0.0001	0.0001	0.0001	0.0001
Site x N	0.0341	0.0003	0.0001	0.0064	0.0002	0.0197	NS	0.0186	0.0008	0.0025	0.0001	0.0101
P rate	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
Site x P	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
N x P	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
Site x N x P	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
K rate	NS	NS	NS	NS	NS	NS	NS	NS	NS	0.0356	NS	NS
Site x K	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
N x K	NS	NS	NS	NS	NS	NS	0.0202	NS	NS	NS	NS	NS
Site x N x K	NS	NS	NS	NS	NS	NS	0.0371	NS	NS	NS	NS	NS
P x K	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
Site x P x K	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
N x P x K	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
Site x N x P x K	NS	NS	NS	NS	NS	NS	NS	NS	NS	0.0015	NS	NS
Contrasts
Linear N	0.0001	0.0002	0.0001	0.0001	0.0001	0.0022	0.0001	0.0001	0.0001	0.0001	0.0001	0.0001
N quadratic	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS
Linear K	NS	NS	NS	NS	NS	NS	0.0290	NS	NS	0.0048	NS	NS
K quadratic	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS	NS

Note: NS, not significant.

Figure 2. Effect of nitrogen (N) fertilizer on SPAD values obtained during the growing season (average of sites). L: linear effect of N rates for a given date: ***, significant at P < .0001.

Figure 3. Effect of nitrogen (N) fertilizer on leaf chlorophyll concentration during the growing season (average for sites). L: linear effect of N rates for a given date: ***, significant at P < .0001.

Figure 4. Effect of nitrogen (N) fertilizer on Dualex₃ values obtained during the growing season (average of sites). L: linear effect of N rates for a given date: ***, significant at P < .0001.

Table 2. Regression equations between leaf N concentrations and chlorophyll concentrations (Chl) and the SPAD, and Dualex₃ values for the different sampling times (average for sites).

Sampling time	Equation	r^2	Probability value
Early July	N (mg g^−1) = −12.70 + 0.93 SPAD	0.27	0.0022
End of July	N (mg g^−1) = −18.38 + 0.92 SPAD	0.75	0.0001
Mid-August	N (mg g^−1) = −6.33 + 0.56 SPAD	0.35	0.0004
End of August	N (mg g^−1) = 0.63 + 0.39 SPAD	0.62	0.0001
Early July	N (mg g^−1) = −3.51 + 0.73 Chl	0.27	0.0022
End of July	N (mg g^−1) = −8.03 + 0.69 Chl	0.75	0.0001
Mid-August	N (mg g^−1) = −0.08 + 0.42 Chl	0.35	0.0004
End of August	N (mg g^−1) = 4.78 + 0.30 Chl	0.61	0.0001
Early July	N (mg g^−1) = 79.63–16.77 Dualex3	0.40	0.0001
End of July	N (mg g^−1) = 57.96–11.45 Dualex3	0.24	0.0049
Mid-August	N (mg g^−1) = 50.17–9.59 Dualex3	0.46	0.0001
End of August	N (mg g^−1) = 41.45–7.06 Dualex3	0.41	0.0001
Early July	N (mg g^−1) = −12.93 + 3.15 × SPAD/Dualex3	0.52	0.0001
End of July	N (mg g^−1) = −8.25 + 2.30 × SPAD/Dualex3	0.73	0.0001
Mid-August	N (mg g^−1) = −2.40 + 1.63 × SPAD/Dualex3	0.54	0.0001
End of August	N (mg g^−1) = 3.70 + 1.13 × SPAD/Dualex3	0.71	0.0001
Early July	N (mg g^−1) = −5.51 + 2.66 × Chl/Dualex3	0.48	0.0001
End of July	N (mg g^−1) = −2.73 + 1.91 × Chl/Dualex3	0.75	0.0001
Mid-August	N (mg g^−1) = 1.42 + 1.36 × Chl/Dualex3	0.52	0.0001
End of August	N (mg g^−1) = 6.25 + 0.95 × Chl/Dualex3	0.71	0.0001

Lafond, J. 2009. Optimum leaf nutrient concentrations for wild lowbush blueberry in Quebec. Can. J. Plant Sci. 89(2):341–347. doi: 10.4141/CJPS08142.

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