1.5.2.2 Nutrient Elements
pH Pristine peat is acidic and includes fewer exchangeable base cations than other
soils. For example, the pH (H 2 O) and pH (KCl) of peat in Central Kalimantan,
Indonesia, are 3.2–3.7 and 1.9–2.2, respectively (Haraguchi, unpublished data).
The pH in tropical peatlands is very low (3.0–3.5) but is not toxic because there is
not much Al
3+ in peat soil. In mineral soil, where aluminum is the main component
together with iron and silica, aluminum becomes ionic Al
3+ at low pH conditions.
Al
3+ is the most toxic ion to plant roots and binds to the cell membrane, destroying
root function. Additionally, as Al
3+ binds strongly to free Pi (inorganic phosphorus),
phosphorus becomes deficient even when large amounts of P are applied to low pH
soil. However, the low pH in tropical peatlands results in macro- and micronutrient
deficiency because (1) few nutrients are provided from precipitation and (2) cation
leaching mechanisms due to cation desorption occur in peat at low pH (less than 4.0)
(Fig. 1.16).
As the pH in tropical peatlands is very low (3.0–3.5), nutrients (cations and
anions) remain very low in tropical peatlands (Fig. 1.11). Thus, nutrients must be
retained only by plants and microorganisms at the peatland surface because it is the
most active layer, suggesting that nutrients are quickly lost due to disturbances at the
peatland surface.
Exchangeable Cations The amount of exchangeable cations in pristine peat is low
(Na
+ : 1–3 mg g
À1 , K
+
: 0–2 mg g
À1 , Mg
2+ : 0–2 mg g
À1 , Ca
2+ : 0–1 mg g
À1 );
however, surface peat in disturbed (e.g., burned) peat swamp forests sometimes
has high levels of exchangeable cations (e.g., K
+
> 20 mg g
À1 , Mg
2+
> 25 mg g
À1 ).
Exchangeable Ca tends to increase from the top to the bottom peat layer and
sometimes exceeds 100 mg g
À1 (Haraguchi, unpublished data). Peat pore water in
a pristine peat swamp forest in Lahei, Central Kalimantan, included low concentrations of major ions (Na
+
< 5 Mg L
À1 , K
+
< 6 Mg L
À1 , Mg
2+
< 2 Mg L
À1 , Ca
2+
<
1 Mg L
À1 , Cl
À
< 8 Mg L
À1 , NH 4
+
< 3 Mg L
À1 , NO 3
À
< 2 Mg L
À1 , SO 4
2À
<
2 Mg L
À1 ; Haraguchi et al. 2000). However, the concentrations of some ions were
extremely high within 1 m of the peat surface (e.g., K
+
> 50 Mg L
À1 , NO 3
À
>
Fig. 1.16 pH of peat water in a peatland in Central Kalimantan
1 Basic Information About Tropical Peatland Ecosystems
25
pH Pristine peat is acidic and includes fewer exchangeable base cations than other
soils. For example, the pH (H 2 O) and pH (KCl) of peat in Central Kalimantan,
Indonesia, are 3.2–3.7 and 1.9–2.2, respectively (Haraguchi, unpublished data).
The pH in tropical peatlands is very low (3.0–3.5) but is not toxic because there is
not much Al
3+ in peat soil. In mineral soil, where aluminum is the main component
together with iron and silica, aluminum becomes ionic Al
3+ at low pH conditions.
Al
3+ is the most toxic ion to plant roots and binds to the cell membrane, destroying
root function. Additionally, as Al
3+ binds strongly to free Pi (inorganic phosphorus),
phosphorus becomes deficient even when large amounts of P are applied to low pH
soil. However, the low pH in tropical peatlands results in macro- and micronutrient
deficiency because (1) few nutrients are provided from precipitation and (2) cation
leaching mechanisms due to cation desorption occur in peat at low pH (less than 4.0)
(Fig. 1.16).
As the pH in tropical peatlands is very low (3.0–3.5), nutrients (cations and
anions) remain very low in tropical peatlands (Fig. 1.11). Thus, nutrients must be
retained only by plants and microorganisms at the peatland surface because it is the
most active layer, suggesting that nutrients are quickly lost due to disturbances at the
peatland surface.
Exchangeable Cations The amount of exchangeable cations in pristine peat is low
(Na
+ : 1–3 mg g
À1 , K
+
: 0–2 mg g
À1 , Mg
2+ : 0–2 mg g
À1 , Ca
2+ : 0–1 mg g
À1 );
however, surface peat in disturbed (e.g., burned) peat swamp forests sometimes
has high levels of exchangeable cations (e.g., K
+
> 20 mg g
À1 , Mg
2+
> 25 mg g
À1 ).
Exchangeable Ca tends to increase from the top to the bottom peat layer and
sometimes exceeds 100 mg g
À1 (Haraguchi, unpublished data). Peat pore water in
a pristine peat swamp forest in Lahei, Central Kalimantan, included low concentrations of major ions (Na
+
< 5 Mg L
À1 , K
+
< 6 Mg L
À1 , Mg
2+
< 2 Mg L
À1 , Ca
2+
<
1 Mg L
À1 , Cl
À
< 8 Mg L
À1 , NH 4
+
< 3 Mg L
À1 , NO 3
À
< 2 Mg L
À1 , SO 4
2À
<
2 Mg L
À1 ; Haraguchi et al. 2000). However, the concentrations of some ions were
extremely high within 1 m of the peat surface (e.g., K
+
> 50 Mg L
À1 , NO 3
À
>
Fig. 1.16 pH of peat water in a peatland in Central Kalimantan
1 Basic Information About Tropical Peatland Ecosystems
25