Ian A. Navarrete

ABSTRACT There is a growing recognition that unless soil hydrophilic fulvic acid (HiFA) is studied together with soil hydrophobic FA (HoFA), we will not fully understand the characteristics of the FA fraction in soils. The aim of this study was to characterize soil HiFA, which were extracted from soil and purified by tangential flow ultrafiltration (TFU), by means of elemental (C, H, O, N, S) and isotope (13C, 15N) analyses, Fourier transform IR (FT-IR) and fluorescence spectroscopy and neutral sugars analysis. Results revealed marked differences between HiFA and HoFA in terms of chemical (elemental, isotopic and neutral sugar compositions) and spectroscopic properties (FT-IR, fluorescence spectra). The HiFA carbon accounted for 46 to 80% of the total FA carbon and thus, an important constituent of the FA fraction. On average, neutral sugars contents in HiFA is twofold larger than in HoFA and are mostly dominated by rhamnose, galactose, and fucose, while in HoFA, mannose was the most abundant neutral sugars, indicating that not only quantity, but also quality of neutral sugars varies between HiFA and HoFA. To further enhance the understanding of the characteristics and composition of soil HiFA including its turnover rate, fate and chemical transformation in soils, it is indispensable to isolate and purify HiFA. As such, purification of soil HiFA by TFU is satisfactory for such purpose.

Large portions of the deforested areas in Southeast Asia in general and in the Philippines in particular have been replaced by grassland, but the dynamics between the soil organic carbon (OC) inputs after forest conversion into grassland and the original OC are poorly understood. Also, quantitative data on the C stabilization is important to understand, assess and predict the long term effect of land-use change, but soil C stabilization mechanisms are not fully considered important when studying land-use change. We measured the soil OC content to depths of 100 cm in paired forest and grassland plots across soil types (i.e., Ferralsols, Andosols, Alisols) in Leyte, Philippines. The natural 13C abundance of the soil organic matter was also analyzed to distinguish between forest- and grassland-derived OC in the grassland soils. Oxalate- and pyrophosphate extractable iron and aluminum oxide concentrations were also analyzed and the relationships between soil mineral phase variables and ...

Abstract: To understand the genesis of soils derived from a late Quaternary sedimentary rock in Leyte, Philippines, the properties of four soil profiles were investigated. Two of the profiles (PS-1, PS-4) derived from coralline limestone were shallow with less developed horizons ...

ABSTRACT The objectives of this study were to verify the effects of using various types of hydrophobic fertilisers to cover dairy slurry on polluting gas emissions and to evaluate the mechanisms by which the reduction of emissions occurred. The hydrophobic fertilisers were prepared by mixing finely ground chemical fertilisers (SP, superphosphate; CC, calcium carbonate; and AP + AS, a mixture of ammonium phosphate and ammonium sulfate) with hydrophobic silica (8% w/w) to make the cover moisture-proof and thus able to. oat on the slurry. Laboratory trials were carried out for 13 days using a pilot scale device. The cumulative volumes of the NH3 and CH4 gases emitted from the digested slurry were considerably higher than those from the raw slurry. In contrast, the volumes of CO2 and H2S gases emitted from the digested slurry were lower than those from the raw slurry. Nitrous oxide was not detected in the present study. The hydrophobic fertilisers composed of SP and AP + AS remarkably reduced the NH3 and CH4 emissions from the digested slurry. None of the fertilisers had an effect on the emissions of CO2 from the raw slurry, but when the digested slurry was covered with the SP and AP + AS fertilisers, an increase in the cumulative volumes of CO2 emissions was induced compared with the control slurry (uncovered), probably due to the relatively high activity of methane-oxidising bacteria. The CC and SP fertilisers were able to reduce the H2S emissions from the raw dairy slurry. The effect of the novel covers on greenhouse gas and other polluting gas emissions varied with the types of chemical fertilisers, depending on acidity or alkalinity, solubility, and the ability to adsorb these gases. The partial dissolution of the nutritional constituents under the hydrophobic fertiliser covering produced changes in the fermentation process of the dairy slurry during storage and consequent gas emissions.

Abstract Very limited data have been published on the nature of strongly weathered soils in geologically young humid tropical islands. The study evaluated the characteristics and formation of 2 strongly weathered soils in the island of Samar, Philippines, one developed ...

Knowledge of the characteristics and fertility status of degraded soil is fundamental to planning suitable soil management strategies for crop production purposes. Such knowledge can be obtained through quantitative appraisal of soil properties and assessment of soil fertility status. Sixty soil samples were collected from five locations at Ormoc, Baybay, Bontoc, Bato and Matalom on the western side of Leyte island, Philippines. An important physical constraint in most of the soils is the high clay content, particularly in the soils of Baybay and Bato where 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. Variation in the physical and chemical constraints of these degraded soils is directly or indirectly related to 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. 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.

The aim of the present study was to describe the effects of land use on humus composition and the structural properties of humic substances (HS) in degraded soil in Leyte, Philippines. Five adjacent land-use types, primary forest (PF), mahogany plantation (MP), rainforestation farming (RF), coffee plantation (CP) and grassland (GR), with comparable geology, parent material, soil type and climate were sampled and examined. The contents of humic acids (HAs), fulvic acids (FAs), polyvinylpyrrolidone (PVP)-adsorbed FAs and PVP-non-adsorbed FAs in the soil, and the elementary composition, infrared (IR) spectra and molecular size distribution of HAs and PVP-adsorbed FAs were compared among the different land uses. Results revealed that conversion of PF into other land uses has led to a decrease in FAs, which were higher under intensive cultivation conditions, such as RF, CP and GR. The amounts of HAs were small and also affected by land use. The amount of PVP-non-adsorbed FAs was more affected by land use than the amount of PVP-adsorbed FAs. Variation in the molecular size of HAs and PVP-adsorbed FAs provided evidence of variations in the structural characteristics of HS as a result of land-use change, although there were no appreciable differences in IR spectra and elementary composition. The relationship between land use and the degree of humification of HAs was poor. The HAs were still in the early stage of humification as indicated by the Type Rp in most soils, the higher contents of elemental H and N, and the high H/C and O/C ratios.

Over the past several decades, the conversion of native forest to agricultural land use has accelerated and featured in the development of Philippine landscapes. This study evaluated the effect of land-use change on soil carbon, nitrogen, neutral sugar composition and other related soil chemical properties in a degraded soil (Typic Hapludult) in Leyte, Philippines. Using a space-for-time substitution (paired-area) approach, soil samples were collected and examined from secondary forest (SF), mahogany plantation (MP), rainforestation farming (RF), coffee plantation (CP) and grassland (GR) of comparable geology, parent material, soil type and climate. Soil pH, exchangeable Ca and Mg, and cation exchange capacity (CEC) tended to be higher after the conversion of deforested cultivated land into MP and RF land-use types. In contrast, land conversion decreased the soil carbon, nitrogen and carbohydrate-C in the order of SF, MP, CP, RF and GR, and the decrease was more marked in RF and GR sites that had been under intensive cultivation for a long period of time. Arabinose and xylose (mainly of plant origin) constituted the major non-cellulosic neutral sugar and represented 31–54% of the total soil carbohydrate-C. Soil carbohydrate-C content contributed 2–8% of the total soil organic carbon because of rapid decomposition of sugars. This suggests an adverse effect of land-use change leading to degradation of soil quality. The results of this study suggest that under the humid tropical climate of the Philippines, high temperature and favorable moisture enhanced the carbohydrate decomposition and, thus, affected the content and composition of neutral sugar in the soil.

This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75–112 m above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation, and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position appear to have dominant effects on the development of the soils.

This study was conducted to evaluate the physical, chemical, and mineralogical characteristics of rain forest soils derived from late Quaternary basaltic rocks in Leyte, Philippines. Four sites along a catena were selected at an elevation of 75-112 m above sea level with an average annual rainfall of 3,000 mm and an average temperature of 28°C. Results indicate that the soils are deep, clayey, and reddish in color, which is indicative of the advanced stage of soil development. They also posses excellent physical condition (friable and highly porous) although they are plastic and sticky when wet as is usual for clayey soils. In terms of chemical characteristics, the soils are acidic with low CEC values and generally low in organic matter and nutrient contents. The clay mineralogy of the soils is dominated by halloysite and kaolinite with minor amounts of goethite and hematite, and they also have generally high dithionite-extractable Fe contents confirming the advanced stage of their development. The soils in the more stable slope positions (PL-1, PL-2, and PL-4) have generally similar characteristics and appeared more developed than the one in the less stable position (PL-3). The most important pedogenic processes that formed the soils appear to be weathering, loss of bases and acidification, desilification, ferrugination, clay formation and translocation, and structure formation. The nature of the parent rock and climatic conditions prevailing in the area as well as slope position appear to have dominant effects on the development of the soils.