pH of around 4 are needed to form taranakite from Andisols. However, even from
cultivated Andisol with high P accumulation, taranakite is not formed by the
addition of 1 mol L
À1 NH 4 Cl and pH adjustment.
6.4.3 Struvite
Struvite (MgNH 4 PO 4 Á6H 2 O) is a major crystalline phosphate in compost
(Komiyama et al. 2013). Swine manure compost and chicken manure compost
have a total P 2 O 5 content of 4–5%. Cattle manure compost has a lower amount.
Struvite plays an important role in recycling P in the soil–plant system.
Figure 6.35a shows pelletized swine manure compost. According to the optical
micrograph (Fig. 6.35b), the struvite is a colorless transparent crystal. Figure 6.35c
shows an SEM image including the same struvite particle and indicating that the
major axis of the crystal is approximately 120 μm. The dashed square d in Fig. 6.35c
includes Mg and P, supporting the conclusion that this crystal is struvite, although N
is lacking in the EDX spectrum due to the property of the window material of the
P
Mg
0
1
2
3
4
5
6
7
8
O
C
N
Pt
Energy [keV]
e
d
d
e
Ca
a
b
c
5
1 5
2 5
3 5
4 5
2θ (degrees, Cu Kα)
f
g
1 cm
Fig. 6.35 Struvite in pelletized swine manure compost. (a) Fermented and pelletized swine manure
(FPSM), (b) optical micrograph of struvite formed in the FPSM, (c) SEM image of a piece of
FPSM, (d and e) EDX spectra of dashed areas (d) and (e) in (c), respectively, (f and g) XRD patterns
of powdered FPSM and reference struvite (Lehr et al. 1967), respectively
6.4 Phosphates Related to Soil-Plant Systems
171