Soil analytical methods

Mineralogy of Soils Overlying the Two Main Geologic Provinces of the El Yunque National Forest, Puerto Rico

Wang Z.. Mineralogy of Soils Overlying the Two Main Geologic Provinces of the El Yunque National Forest, Puerto Rico. A Master Thesis. University of Pennsylvania, 2011.

Abstract: 
A total of twenty 0-20cm soil samples from the El Yunque National Forest, Puerto Rico, have been analyzed using XRD analysis to determine their mineral content. Qualitative and quantitative analysis of the data show that all the samples contain quartz, orthoclase, kaolinite, dickite, halloysite and nicrite, gibbsite, augelite, metavariscite, goethite, tsaregorodtsevite, apophylite. Soil sample from Oxisols sites contain higher percentage of clay minerals than the samples from Dystrudepts sites. Furthermore, the general pattern of the percentage of total clays, feldspars, and gibbsite within each and between transects suggest that soils in the valleys are more weathered and leached than soils from ridges. The percentage increase of phosphate minerals in the soils follow that of clay minerals which is most probably due to the attachment of the phosphate minerals to clay mineral surfaces. The presence of the organic cation Tetramethylammonium in the cavities between the oxygen-silicon tetrahedra of the tsaregorodtsevite structure (feldsphoid-zeolitic structure) is consistent with a low energy mechanism for the sequestration of carbon and nitrogen in the EYNF soils.

Estimating soil labile organic carbon and potential turnover rates using a sequential fumigation–incubation procedure

Zoua, X.M.; Ruanc,H.H.; Fua, Y.; Yanga, X.D.; Sha, L.Q. 2005. Estimating soil labile organic carbon and potential turnover rates using a sequential fumigation–incubation procedure.. Soil Biology & Biochemistry 37 :1923-1928.

Abstract: 
Labile carbon is the fraction of soil organic carbon with most rapid turnover times and its oxidation drives the flux of CO2 between soils and atmosphere. Available chemical and physical fractionation methods for estimating soil labile organic carbon are indirect and lack a clear biological definition. We have modified the well-established Jenkinson and Powlson’s fumigation–incubation technique to estimate soil labile organic carbon using a sequential fumigation–incubation procedure. We define soil labile organic carbon as the fraction of soil organic carbon degradable during microbial growth, assuming that labile organic carbon oxidizes according to a simple negative exponential model. We used five mineral soils and a forest Oa horizon to represent a wide range of organic carbon levels. Soil labile organic carbon varied from 0.8 mg/g in an Entisol to 17.3 mg/g in the Oa materials. Potential turnover time ranged from 24 days in an Alfisol to 102 days in an Ultisol. Soil labile organic carbon contributed from 4.8% in the Alfisol to 11.1% in the Ultisol to the total organic carbon. This new procedure is a relatively easy and simple method for obtaining indices for both the pool sizes and potential turnover rates of soil labile organic carbon and provides a new approach to studying soil organic carbon.
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