Morphology, physiochemical characteristics, and fertility of soils from quaternary limestone in leyte, philippines

Very few studies have been conducted on the nature and characteristics of soils from Quaternary limestones in geologically young islands in the humid tropics. This study examined a hillslope in Leyte, Philippines, with soils from Quaternary (Late Pleistocene) limestone and evaluated their morphology, physiochemical characteristics, and fertility constraints. We evaluated six pedons representing different slope positions, such as summit, shoulder, upper backslope, middle backslope, lower backslope, and footslope. Our data indicate that the soils in the upper slopes (summit, shoulder, and upper backslope) have thin solum, black surface horizon, clayey texture, granular structure, high organic matter and N, high Ca and CaCO3 contents, low contents of nutrients like P, K, Fe, Mn, and B, and are neutral to alkaline pH values. According to Soil Taxonomy, the soils are classified as Typic Calciudolls (summit) and Rendollic Eutrudepts (shoulder and upper backslope), but all three pedons are classified as Calcaric Phaeozems in the World Reference Base system. Conversely, the soils on the lower slopes (footslope and middle and lower backslopes) have thicker solum and higher clay content. They have subangular blocky structures, which turn hard when dry and become plastic and sticky when wet. Like the soils on the upper slopes, they also have neutral to strongly alkaline pH values, have high organic matter, N, Ca, and CaCO3 contents, but are generally low in nutrient contents. They are classified as Typic Eutrudepts (source, Soil Taxonomy) or Calcaric Cambisols (source, World Reference Base). Most soils have high rock fragment contents in their profile. Results also show substantial variations of solum depth at short distances along the slope (i.e., from summit to footslope) and across the slope. The solum depth variability helps explain the commonly observed variations of crop growth in limestone areas. The high clay content of these relatively young soils suggests contribution from limestone parent material and possibly volcanic ash from past eruptions of nearby volcanoes. Our results show that soils developed from limestone have both physical and chemical fertility constraints to upland crop production, which differ between soils even in the same landscape. The overall results indicate that the characteristics and fertility constraints of soils from Quaternary limestones in our study site are largely the influence of the slope position, chemical characteristic of the limestone parent material, and human activities.