Soil degradation in the Philippines

Soil degradation is a severe global problem of modern times. About six (6) million hectares of agricultural land worldwide become unproductive every year due to the various soil degradation processes. The problem is much more serious in tropical than in temperate areas since tropical soils are generally more prone to degradation because of the nature of their properties (e.g. they are more weathered) and the prevalent climatic conditions. Countries in Asia and Africa that depend upon agriculture as the engine of economic growth are believed to suffer the greatest impact of soil degradation. In the Philippines, soil degradation is one of the most serious ecological problems today. The National Action Plan (NAP) for 2004 to 2010 identified soil degradation as a major threat to food security in the country. NAP reported that about 5.2 million hectares are seriously degraded resulting in a 30 to 50% reduction in soil productivity.

A degraded upland in Leyte

Soil degradation is defined as the process which lowers the current or future capacity of the soil to produce goods or services. It implies a long-term decline in soil productivity and its environment-moderating capacity. The concept of soil degradation was first used by Kostychiev and Korchinski in 1888 to describe a natural soil change. Since natural degradation is slow, the present concept of soil degradation according to the Global Assessment of Soil Degradation (GLASOD) focuses on a human-induced process. Soil degradation occurs because of drastic changes or disruption in the normal processes of soil formation due to human activities.

A degraded upland covered with Imperata (cogon) grass in Samar

In a review paper on the problem of soil degradation in the Philippines published in the Annals of Tropical Research vol. 31, we (Asio et al. 2009) revealed that soil erosion is the most widespread process of soil degradation and is also the most studied in the country. Other important but less studied soil degradation processes include loss of nutrients and organic matter, salinization, acidification, pollution, compaction, and subsidence. 

A degraded upland in Bukidnon

Studies reviewed have shown that the widespread degraded upland soils possess chemical and physical constraints for crop growth like acidic or calcareous pH, low organic matter and nutrient contents, shallow solum, presence of toxic substances, and compaction. The major factors that cause soil degradation include deforestation, overgrazing, agricultural practices, industrial activities, mining, and waste disposal. Deforestation is the main cause of soil degradation in Asia and South America while overgrazing is the main factor in the dryland areas of Australia, Africa, Europe, and Asia.

The typical degraded land in Cagayan Valley due to deforestation & overgrazing 

There is a need for more data on the physical and socio-economic characteristics of degraded lands to aid in the formulation of appropriate soil management strategies to support biodiesel production in these unproductive lands which are now being promoted by the Philippine government. Also, there is the danger that the use of the degraded lands for intensive and long-term biodiesel production without the appropriate soil management would cause further soil deterioration and thus aggravate the ecological problems that are now occurring.

Reference

Asio VB, Jahn R, Perez FO, Navarrete IA, and Abit SM Jr. 2009. A review of soil degradation in the Philippines. Annals of Tropical Research 31: 69-94

Note: All photos are owned by the author.

The Physical Environment of Mt. Pangasugan, Leyte, Philippines

Geology

Mt. Pangasugan is generally built up by andesitic and basaltic pyroclastic rocks (referred to as Pangasugan formation) which are mostly of Quaternary and Tertiary origin. This rock formation is characterized by weak consolidation, lithologic discontinuities, abundance of rock outcrops, and shearing due to the occurrence of the Philippine fault line approximately at the center of the mountain range. Minor earthquakes are relatively frequent in the area. All these geological characteristics indicate that the area is unstable.

Geomorphology

The morphology of Mt. Pangasugan is largely the result of the combined effects of volcanism, erosion, faulting and tectonic uplift. Mt. Pangasuagn rises abruptly from the narrow alluvial coastal plain along the Camotes Sea into a vertical wall-like rock mass with a maximum height of about 1100 m above sea level (asl). The air distance between the sea level and the peak of the mountain is less than 3 km. This short distance suggests extremely high erosion energy potential which is visible in the form of waterfalls particularly during periods of high rainfall. The west-facing slope of the mountain is deeply dissected by several short parallel streams that empty into the Camotes Sea. The V-shaped valleys, which indicate youthful stage, coupled by the unconsolidated nature of the rock material, cause widespread landslides during typhoon periods.

Climate

The climate of the area is a humid tropical monsoon climate with no pronounced maximum rain period and no dry season (Type 4 of the Coronas climatic classification). It has an average annual rainfall ranging from 2600 mm in the coastal lowland, to more than 3000 mm at higher elevations. Average temperature in the plain is 27 degrees Celsius which decreases by an average of 0.6 degree Celsius per 100 m rise in elevation (i.e. at 500 m elevation, the average temperature is 24 degrees Celsius). Two types of monsoon winds tremendously influence the over-all climate of the area. From June to October, a southwest monsoon (Habagat) occurs which enhances rainfall in the area (western side of mountain). From November to February, the northeast monsoon (Amihan) follows which generally coincides with cyclonic disturbances thereby bringing plenty of rain particularly to the eastern side of the mountain range.

Pedology

The soils of the mountain can be grouped into four: the old soils in the mountain footslopes (approximately below 200m asl), the mature soils in the mountain midslopes (approximately between 200 and 400m asl), the young soils in the upper slopes (approximately above 400m asl) and the undeveloped soils in very steep slopes.The old soils (Ultisols) are deep, clayey, acidic and infertile. They are relatively stable although landslides may occur. The mature soils (Alfisols) are generally fertile and productive. The young soils in the upper slopes (Andisols) result from the fast weathering of andesitic rocks. They have excellent physical condition but are acidic and generally low in phosphorus. Because of their weak profile development and amorphous clay mineralogy, these soils are unstable and prone to landslides and erosion. The undeveloped soils on steep slopes (Inceptisols and Entisols) have low productivity due to their shallow profile, abundance of rock fragments and steep slopes. They are also prone to erosion.

References

Asio V.B.1996. Characteristics, weathering, formation and degradation of soils from volcanic rocks in Leyte, Philippines. Hohenheimer Bodenkundliche Hefte 33, Stuttgart, Germany, 290pp.

Quimio, J.M., V.B. Asio, J.M. Alkuino, B.B. Dargantes and P.S. Muga. 1997. Initial Environmental Examination of the Leyte-Mindanao Interconnection Project. NPC, Quezon City, 151pp.

Biological nitrogen fixation in corn

Corn (Zea mays L.) can establish rhizospheric or endophytic associations with various nitrogen-fixing bacteria (diazotrophs) such as Azospirillum, Klebsiella, Pantoea, Herbaspirillum, Bacillus, Rhizobium etli and Burkholderia. Most of these diazotrophs can grow in the intercellular tissue of plants without causing any disease.

Biological nitrogen fixation (BNF) is the biological process by which nitrogen (N2) in the atmosphere is converted to ammonia by an enzyme called nitrogenase. The screening of plant genotypes for their enhanced ability to acquire nitrogen by BNF can reduce the use of expensive nitrogen fertilizers in several important crops like sugarcane, rice, wheat and corn. It can greatly benefit particularly the poor farmers of developing countries.

In a recent study aimed to quantify the symbiotic biological nitrogen fixing activity of a range of commercial corn cultivars, Montanez et al. (2009) demonstrated that corn cultivars obtain significant nitrogen from BNF, the level of which varied with corn cultivar and nitrogen fertilization level. The study showed that some cultivars were more sensitive than others to nitrogen application and that 15N isotope dilution method is a useful tool to screen and select corn cultivars with any potential BNF.

Reference

Montanez A, Abreu C, Gill PR, Hardarson G, and Sicardi M. 2009. Biological nitrogen fixation in maize (Zea mays L.) by 15N isotope dilution and identification of associated culturable diazotrophs. Biology and Fertility of Soils 45: 253-263