Nutrient addition as a forest restoration management strategy for Yakal yamban seedling establishment in ophiolitic soils

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 literatures, 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 the 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 an ophiolitic soils, 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 labelled plastic bags ready for air-drying and analysis.

Major Findings

Results revealed highly significant differences in leaf area, percent biomass allocation, and 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 theroots 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 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