Table 1.

The concentrations of involved variables at different levels and the regression analysis of the Plackett-Burman design.

No.	Variables	Concentration (g/L)		Effect	Coefficients	Standard Error	t-Value	p-Value
		−1 Level	+1 Level
X1	Wheat bran	1.0	5.0	2.003	1.002	0.1868	5.36	0.003 a,**
X2	Kelp powder	0.1	1.0	−1.383	−0.692	0.1868	−3.70	0.014 b,*
X3	Glucose	0.1	0.5	−2.023	−1.012	0.1868	−5.42	0.003 b,**
X4	NaNO3	0.01	0.05	4.320	2.160	0.1868	11.56	0.000 a,**
X5	MgSO4·7H2O	0.01	0.05	2.860	1.430	0.1868	7.66	0.001 a,**
X6	NaCl	0.1	1.0	5.110	2.555	0.1868	13.68	0.000 a,**

R² = 98.90%; R²_Adj = 97.59%; R²_Pre = 93.69%; Non-significant at p < 0.05; ^a Significant positive effect; ^b Significant negative effect; * <0.05; ** <0.01.