by Johannes R. G. Asio
Institute of Tropical Ecology and Environmental Management (ITEEM),VSU, Baybay City, Leyte, Philippines
Introduction
Dipterocarp trees (Dipterocarpaceae)
have crucial ecological roles such as in the prevention of landslides,
sequestration of atmospheric carbon, and biodiversity. They are also economically
important in terms of timber production. These native trees are also adapted to
a variety of climatic conditions and geographic locations (e.g. areas prone to
heavy typhoons, marginal lands). However, the sustainable management of dipterocarp
forests is still poorly understood due to the limited studies conducted on the
subjet. This is particularly so in terms of the ability of these forest trees to
thrive in marginal lands like those naturally contaminated with heavy metals
and those soils with very low nutrient status such as ophiolitic and
serpentinite areas (Corlett&Primack, 2006; DENR, 2012; Appanah, 1998;
Walpole, 2010).
Ophiolite rocks are widespread in Leyte, Samar, Cebu and
Palawan. These rocks generally underlain marginal lands. A typical ophiolite
complex is a stratified igneous rock complex that consists of different rock
layers: an upper basalt member, a middle gabbro member, and a lower peridotite
member (Ishiwatari, 2016). The fertility of Ophiolite rocks in the Philippines
has not yet been studied in detail, however, according to some literature, it
is generally moderately acidic to neutral, low soil organic matter, low
nitrogen (N), phosphorus (P), and potassium (K), which are the major nutrients
needed for plant growth, and it contains high amounts of heavy metals, such as
chromium, nickel, iron, and cobalt among others (Dimalanta et al., 2006; Ocba, 2016).
Mineral fertilizers have been used in agriculture and
forestry to improve crop yield, enhance soil fertility, and soil health.
Thus, this study hypothesized that the addition of N, P, and K to an ophiolite
soil could enhance the growth of Yakalyamban (Shorea falciferoides Foxw.) in problematic areas. This dipterocarp
species was chosen for this research as it has been known to thrive in the
ophiolitic and serpentinite areas of Samar and it is critically endangered,
thus the need to preserve this dipterocarp to prevent it from becoming extinct
(Fernando et al., 2009, 2008).
This study aimed to test whether the addition of nutrients enhanced
the seedling growth of yakal yamban grown in ophiolitic soil, determine the
optimum nutrient combination level for yakalyamban seedling quality; and assess
and evaluate whether fertilization could very well be adopted as a nutrient
management practice in using yakal yamban as a rainforestation species for forest
restoration in problematic soils.
Methodology
The potting medium was selected based on the soil data obtained
by the VSU-OXFAM Project (2015). Detailed soil analysis done by the project
showed that the soils in Barangay Padang, Hernani, Eastern Samar developed from
ophiolitic rocks and have low levels of N,P,K, and Mg, but high levels of Ca.
Twenty sacks of topsoil (0-30cm depth) were collected and transported to the
Terrestrial Ecosystems Division of the Institute of Tropical Ecology and
Environmental Management for this screenhouse experiment. The bulk soil samples
were mixed, air-dried thoroughly, pulverized, and sieved using a 4-mm mesh
sieve. About 1.5 kg of the air-dried soil was weighed; 0.75 kg sieved soil
(from the 4-mm sieve) and 0.75 kg unsieved soil to avoid soil compaction.
This one-year study was conducted using a 5 x 3 Randomized
Complete Block Design (RCBD) with five treatments and three replicates, wherein
each treatment per replication consisted of 10 seedlings. The treatment are as
follows: T1- No fertilizer application, T2- Application
of 3.65 g of Urea, 9.33 g of Solophos, & 2.8 g of Muriate of Potash, T3-
Application of 3.65 g of Urea, 9.33 g of Solophos, T4- Application
9.33 g of Solophos& 2.8 g of Muriate of Potash, T5- Application
of 3.65 g of Urea & 2.8 g of Muriate of Potash. Placement application was
done wherein the exact amount of fertilizer for each seedling was applied a few
centimeters below the soil surface. Tap water was used. About 400 mL was added
as required.
Three (3)
randomly selected seedlings in each replication were harvested after 3 months
and 6 months from fertilizer application. The selected seedlings were
photographed before and after harvest, documenting each plant part, and making
notable observations. Thereafter, each individual seedling was cut; each leaf
was photographed in preparation for leaf area analysis. Then, each plant part
(roots, stem, and leaves) was separated and placed into the corresponding paper
bags ready for oven drying. The soil samples in each replication were mixed and
placed into labeled plastic bags ready for air-drying and analysis.
Major Findings
Results revealed highly significant differences in leaf area,
percent biomass allocation, and the root-shoot ratio between treatments 6 months
after sampling. In terms of leaf area, treatment 4 showed the highest leaf area
value. All treatments added with phosphorus (treatments 2,3 and 4)
had leaf area values that were statistically the same. This indicates that P is
the most critical nutrient in the soil and that this tree species is sensitive
to the P levels in the soil.
There were also significant differences in terms of the
percent biomass allocation between treatments in the root, stem, and leaves,
with treatment 5 showing the highest allocation in the roots; plants
in P-deficient environments enhance root growth as it is their adaptive
mechanism that enables them to thrive in these conditions. The result also
coincides with the root-shoot ratio as study plants in treatment 5 had the
highest root-shoot value.
Soil nutrient analysis was done to determine the nutrient status of each treatment. The analyses concur with the fact that ophiolitic soils are deficient with N, P, & K, thus the high values of the nutrients were due to the fertilizers added prior to destructive harvesting. It was also observed that the fertilizer treatments have not yet fully dissolved even after 6 months of application.
Plant nutrient concentration was also done to determine
the nutrient content of each plant part. In terms of nitrogen (N), there were
high values of N in the leaves as it is needed for photosynthetic activity.
However, it was below the optimum concentration needed for plant growth
(Marschner, 1995). With regards to P, there were high values of the nutrient in
treatments not added with P. It may be due to the mycorrhizae present in the
roots of the study plants after 6 months of application. For K, solubility
played a factor since there was an inhibition of nutrients to be taken up
especially between N and K.
The presence of ectomycorrhizae (EcM) was also observed
in the
roots of the study plants of the control (T1) and NK (T5).
Various studies have proven that mycorrhiza aids in the growth of a plant as it
enhances the absorption of nutrients and water (Marschner, 1995; Read, 1991).
The result also coincides with the study of Turner et al., 1992 as EcM
infection may serve as a purpose when dipterocarps are grown in nutrient-poor
conditions.
Implications
Nutrient addition could very well be adapted as a
nutrient management strategy for the seedling establishment of Yakal yamban in ophioitic
soils; Treatment 5 enhanced the root-shoot ratio of the study plants, thus
these seedlings are of good quality. This implies that during the establishment of
the seedlings in an open area, they are most likely to survive due to its
adaptive mechanism (e.g. enhance root growth in p-deficient environments) and
the potential fungus-root association in the soil.
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The above article is a summary of the BSEM thesis by the author which won as 2017 Phi Delta Outstanding Thesis in Applied Biological Sciences at VSU, Baybay City, Leyte. More information can be obtained from the author. Email: johannes.asio@vsu.edu.ph
The above article is a summary of the BSEM thesis by the author which won as 2017 Phi Delta Outstanding Thesis in Applied Biological Sciences at VSU, Baybay City, Leyte. More information can be obtained from the author. Email: johannes.asio@vsu.edu.ph
