Characteristics and fertility constraints of degraded soils in Leyte, Philippines

Contributed by
Dr. Ian A. Navarrete
Humboldt Fellow
Soil Science of Tropical and Subtropical Ecosystems
Georg-August Univesity Göttingen
Gottingen, Germany

Soil degradation, a process that lowers the capacity of the soil to produce goods or services, is a prevalent agricultural and environmental problem in the Philippines (Asio et al. 2009). However, to date, the nature and characteristics of degraded soils in the Philippines have been poorly understood, in that there have been few studies on this subject (Asio et al. 2009; Navarrete et al. 2009). Although various crop production technologies have been developed for marginal areas these technologies have not been successfully adapted by farmers or have failed to alleviate crop production (Cramb 2001). Cramb further stated that the introduction of unsuitable soil management technologies to farmers has intensified the soil degradation processes occurring in these areas. Thus, knowledge on the characteristics and fertility status of degraded soil is fundamental in planning suitable soil management strategies for crop production purposes. Because the degree of soil degradation immensely varies among sites depending on soil forming factors, soil management strategies must be location specific, every degraded soil has to be evaluated in terms of its properties and constraints.

In our recent study published in the international journal Archives of Agronomy and Soil Science (Navarrete et al. 2012), 60 soil horizon samples were collected from five locations (across an elevation gradient between 97 and 735 m above sea level) at Ormoc, Baybay, Bontoc, Bato and Matalom on the western side of Leyte island, Philippines. The samples were subjected to various physical, chemical and mineralogical analysis. Results revealed that the most important physical constraint in most of the soils evaluated is the high clay content particularly in the soils of Baybay and Bato because it is a problem for cultivation. The strongly acidic and strongly alkaline pH, low available P and, in some cases, low exchangeable K are the chemical constraints. Most of the variations in the physical and chemical constraint of these degraded soils can be explained directly or indirectly by the nature of the parent material, geomorphic position and anthropogenic effect. Soil fertility characteristics are distinct within similar soil types, primarily because they are related to the dominant soil-forming processes (see for example Figure 1 below). Consideration of the soil physical and chemical constraints is essential for the long-term planning of soil management strategies that will lead to sustainable utilization of these problematic soils.


Figure 1. Plots of the first and second principal components (PC) extracted from the principal component analysis (PCA) of all selected properties. (a) distribution of soil samples and soil types (b) distribution of soil properties



References
Asio VB, Jahn R, Perez FO, Navarrete IA, Abit SM, Jr. 2009. A review of soil degradation in the Philippines. Annals Tropical Research 31: 69-94.
Cramb RA (ed). 2001. Soil conservation technologies for smallholder farming systems in the Philippine uplands: a socioeconomic evaluation, ACIAR, Australia.
Navarrete IA, Tsutsuki K, Asio VB, Kondo R. 2009. Characteristics and formation of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Environmental Geology 58: 1257-1268.
Navarrete IA, Tsutsuki K, Asio VB. 2012. Characteristics and fertility constraints of degraded soils in Leyte, Philippines. Archives of Agronomy and Soil Science. DOI /10.1080/03650340.2012.663908

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