there is a surface layer that mainly comprises the tree roots overlying the less
consolidated, semiliquid peat with an abundance of tree remains. The only supply
of water and chemical elements to the interior of this peatland ecosystem is from
rainfall; consequently, the nutrient cycle is very important in maintaining forest
biomass (Maltby et al. 1996; Page et al. 2006). Seasonal variations in rainfall and
water table movement also affect the fluctuations in the soil solution composition
(Marwanto et al. 2018).
Extensive forest exploitation following peat drainage for agricultural expansion
leads to catastrophic peat fires (Langner and Siegert 2009; Yulianti et al. 2012). Peat
is formed through the plant biomass accumulation process when the biomass
decomposition rate is slower than the biomass growth thereof. Because peat formation generally occurs in swampy soils and is dominated by organic matter, peatland
has different characteristics than other land types. Peatlands generally have very low
density and high water porosity. Chemically, peatlands have low pH, nutrient
content, and oxygen levels. Peatlands may be suitable for agriculture if all the
limiting factors mentioned are addressed. The difference between subtropical and
tropical peatlands is their vegetation type. Tropical peatlands consist of woody
plants and therefore have high levels of lignin.
The key limiting factors on plant growth in tropical peatland are oxygen and
nutrients. The availability of oxygen in peat water is very limited due to the low
capability of oxygen to solubilize in acidic water conditions. Nutrients are also
limited in peat soils because of the low nutrient absorption ability at low pH (less
than 4.0), leading to nutrient leaching even when a high rate of fertilizer is applied.
Most of the water supply comes from rain that has no nutrient content. Plant roots
require oxygen to absorb nutrients. A high rate of oxygen is needed because the
active energy process requires nutrient absorption (without oxygen, there can be no
nutrient absorption). Oxygen is also required by the nodules of legume plants for the
N 2 fixation process.
Only a limited number of plants can survive in peatlands due to their unique
characteristics. In most cases, many cultivation areas apply drainage systems that
lead to the drainage of peat water. Typical conventional oil palm cultivation maintains the water at a low level (50–70 cm) and includes the application of a large
amount of fertilizer, especially K
+ . However, oil palms show very serious K
+
deficiency symptoms in their leaves, indicating that most of the K
+ fertilizer applied
is leached away. K
+ becomes a limiting factor because the cation charge of organic
matter (peat soil) is extremely low at low pH (less than 4.0). If a typical fast-release
fertilizer is applied to a peat soil, all its nutrients leach out immediately due to
desorption mechanisms, especially K
+
. K
+ always exists in ionic form (it does not
form compounds); therefore, it leaches easily. Other nutrients are absorbed to some
extent into microorganisms and form chemical compounds; these compounds are
then retained and decompose slowly in the peat layer. Other nutrient cations may
also chelate with organic acids and become unavailable to crops. Other nutrient
impacts are indicated by the root condition. When K
+ is deficient, root growth is poor
since K
+ plays a role in photosynthate translocation into the root. When root growth
is poor, low nutrient absorption occurs, and thus, a negative feedback loop is
7 Principles of AeroHydro Culture
269
consolidated, semiliquid peat with an abundance of tree remains. The only supply
of water and chemical elements to the interior of this peatland ecosystem is from
rainfall; consequently, the nutrient cycle is very important in maintaining forest
biomass (Maltby et al. 1996; Page et al. 2006). Seasonal variations in rainfall and
water table movement also affect the fluctuations in the soil solution composition
(Marwanto et al. 2018).
Extensive forest exploitation following peat drainage for agricultural expansion
leads to catastrophic peat fires (Langner and Siegert 2009; Yulianti et al. 2012). Peat
is formed through the plant biomass accumulation process when the biomass
decomposition rate is slower than the biomass growth thereof. Because peat formation generally occurs in swampy soils and is dominated by organic matter, peatland
has different characteristics than other land types. Peatlands generally have very low
density and high water porosity. Chemically, peatlands have low pH, nutrient
content, and oxygen levels. Peatlands may be suitable for agriculture if all the
limiting factors mentioned are addressed. The difference between subtropical and
tropical peatlands is their vegetation type. Tropical peatlands consist of woody
plants and therefore have high levels of lignin.
The key limiting factors on plant growth in tropical peatland are oxygen and
nutrients. The availability of oxygen in peat water is very limited due to the low
capability of oxygen to solubilize in acidic water conditions. Nutrients are also
limited in peat soils because of the low nutrient absorption ability at low pH (less
than 4.0), leading to nutrient leaching even when a high rate of fertilizer is applied.
Most of the water supply comes from rain that has no nutrient content. Plant roots
require oxygen to absorb nutrients. A high rate of oxygen is needed because the
active energy process requires nutrient absorption (without oxygen, there can be no
nutrient absorption). Oxygen is also required by the nodules of legume plants for the
N 2 fixation process.
Only a limited number of plants can survive in peatlands due to their unique
characteristics. In most cases, many cultivation areas apply drainage systems that
lead to the drainage of peat water. Typical conventional oil palm cultivation maintains the water at a low level (50–70 cm) and includes the application of a large
amount of fertilizer, especially K
+ . However, oil palms show very serious K
+
deficiency symptoms in their leaves, indicating that most of the K
+ fertilizer applied
is leached away. K
+ becomes a limiting factor because the cation charge of organic
matter (peat soil) is extremely low at low pH (less than 4.0). If a typical fast-release
fertilizer is applied to a peat soil, all its nutrients leach out immediately due to
desorption mechanisms, especially K
+
. K
+ always exists in ionic form (it does not
form compounds); therefore, it leaches easily. Other nutrients are absorbed to some
extent into microorganisms and form chemical compounds; these compounds are
then retained and decompose slowly in the peat layer. Other nutrient cations may
also chelate with organic acids and become unavailable to crops. Other nutrient
impacts are indicated by the root condition. When K
+ is deficient, root growth is poor
since K
+ plays a role in photosynthate translocation into the root. When root growth
is poor, low nutrient absorption occurs, and thus, a negative feedback loop is
7 Principles of AeroHydro Culture
269