Soil Fertility, Phosphorus Fractions, and Maize Yield as Affected by Poultry Manure and Single Superphosphate

Table 2

Sequential P fractionation procedures and targeted P forms.

Location	Extractants	Equilibration	Washing	Targeted
NH4Cl-P	IM NH4Cl	30 mins	None	Saloid-bound P; (loosely bound P)
NH4F-P	0.5 M NH4F	1 hour	None	Al-P
NaOH-P	0.1 M NaOH saturated; Nacl + 5 drops of conc. H2SO4	15 mins	Saturated Nacl	Fe-P
Sodium + citrate; Sodium dithionite P	0.3 M sodium citrate + 1 g solid; Sodium dithionate + sat Nacl	Shake 15 mins, preheat 15 mins at 85°C after sodium citrate, additional 15 mins after dithionite addition	Saturated Nacl	Reductant-soluble P
NaOH-P	0.1 M NaOH + few drops of conc. H2SO4 to remove colour	15 mins	Saturated NaCl	Occluded P
H2SO4-P	0.25 M H2SO4 + 25 mL Sat. Nacl	1 hour	Saturated Nacl	Ca-P
Residual P	Conc. HNO3 + HCl + 30% H2O2	Variable until complete	None	Organically stable organic and inorganic P