Causes for the small scale variability of nitrate concentration in seepage water of an N saturated mature spruce stand

Table 3 Summary of the final linear regression models explaining the variability of \( {\text{N}}{{\text{O}}_3}{^{ - }_{\text{seepage}}} \) at the different sampling dates

		Standardized regression coefficient (beta) of significantly included variables
Parameter (layer)^a		Unit	April	May 1	May 2	June	July	August	September	October	April–October
1	Net N mineralization (0)	mg N kg⁻¹ day⁻¹	0.64	0.65	0.65	0.67	0.69	0.73	0.58	0.52	0.62
2	Roots <2 mm (1–3)	g m⁻²	0.34	0.37	0.4	0.41	0.37	0.35	0.38	0.41	0.41
3	Roots <2 mm (4)	g m⁻²					−0.17	−0.17	−0.30	−0.34	−0.15
4	Roots 2–5 mm (3)	g m⁻²	−0.18	−0.17	−0.16	−0.14
5	Basal area circ. 4 m	cm³	−0.31	−0.27	−0.25	−0.22	−0.15				−0.21
6	Pore volume <10 μm (3)	vol.%	–	–	–	–
7	pH H₂O (3)							–	–	–	–
8	Cover oxalis	% coverage									–
	Sum beta²		0.65	0.66	0.67	0.69	0.66	0.68	0.57	0.55	0.62
	Adjusted multiple R ²		0.87	0.88	0.89	0.89	0.93	0.89	0.79	0.79	0.90

Shown are the standardized regression coefficients for each significant parameter and the sum of the squared beta values (sum beta²) and the adjusted multiple R ² for the whole model
(–) parameter was originally included into the model but lead to high collineartity indexes and was therefore removed
^a(0) = organic layer, (1–4) = mineral soil layers from 0 to 10 (1), 10–20 (2), 20–30 (3), and 30–40 cm (4)

ISSN: 1297-966X