Impact of Forage Fertilization with Urea and Composted Cattle Manure on Soil Fertility in Sandy Soils of South-Central Vietnam

Table 4

Soil chemical models in 0 to 15 cm and 15 to 25 cm strata selected from candidate fixed effects of compost (C), urea (U), compost × urea (C × U), preexperiment soil fertility for each parameter sampled at 15 to 25 cm depth (PSF), and significant interactions, with block included as a random effect.

Parameter	0 to 15 cm depth		15 to 25 cm depth
	Model effect	Farm (%)	Model effect	Farm (%)
S (mg/kg)	C × U × PSF	82	C × U × PSF	85
Mg (mg/kg)	C × U × PSF	87	C × U × PSF	89
Zn (mg/kg)	C × U × PSF	28	C × U × PSF	16
Mn (mg/kg)	C × PSF	87	C × U × PSF	49
OM (g/kg)	C × U × PSF	65	U × PSF	77
K (mg/kg)	C × PSF	51	C × PSF	60
Cu (mg/kg)	C × U × PSF	62	PSF	53
CEC (cmol+/kg)	PSF	31	C × U × PSF	46
P (mg/kg)	PSF	52	C × U × PSF	28
NH4-N (mg/kg)	PSF	66	PSF C × U	42
pH (1 : 1 soil : water)	C PSF	88	PSF	75
Fe (mg/kg)	PSF	88	PSF	70
Al (mg/kg)	PSF	62	PSF	58
NO3-N (mg/kg)	PSF	43	PSF	46
Ca (mg/kg)	C × U	75	PSF	49
Na (mg/kg)	PSF	47	C × U	49
B (mg/kg)	NS	—	NS	—

Where interactions were significant, only highest level interactive effect or effects are shown, although lower level terms were also in the model.
Each row represents a single model for each soil depth.
Percentage of residual variance explained by farm in each model is indicated.