Table 2: Statistical evaluation of the effects of soil type, biochar concentration, and biochar feedstock and their interactions on the aqueous-phase concentration or extractability of enzyme assay substrates and products, respectively, used in soil dehydrogenase and phosphatase assays. The ANOVA was conducted using general linear model (Minitab 16) with ranked data ( ).

SourcePhosphataseDehydrogenase
Substrate
p-nitrophenyl phosphate
Product
p-nitrophenol
Substrate
Iodonitrotetrazolium chloride
Product
Iodonitro-tetrazolium formazan
DF value

Soil type (Kettering loam; Cameroon Oxisol)1<0.001<0.001<0.001 0.088
Biochar feedstock (straw; pinewood shavings)10.0020.0160.024<0.001
Biochar concentration
(0, 15, 30, 150 mg g−1)
3<0.001<0.001<0.001<0.001
Soil * feedstock * conc30.3390.037 0.2610.003
Soil * feedstock10.1150.0020.004<0.001
Soil * conc.30.0140.4740.0130.013
Feedstock * conc.30.2700.3310.003<0.001
Error48

Total63