Soil textural and organic matter analysis is a key component for assessing soil quality and sustainability of agricultural-management practices (Kettler et al. 2001). Particulate organic matter (POM) is defined as all soil organic matter particles in size of 53 to 2000 μm and is dominated by undecomposed plant residues that retain recognizable cell structures. POM is an estimate of labile soil organic matter and a good indicator of land management. Soil particle size distribution is the distribution of primary particles in the soil, including sand, silt, and clay. Soil texture can be determined by its particle size distribution, which affects many soil properties, such as nutrient storage and soil-water retention characteristics.
Kettler et al. have developed a rapid method for measurement of POM and particle size distribution using a gravimetric approach. However, inconsistent data were obtained from previous soil health research using the rapid method. Therefore, the objective of this project was to identify factors affecting the measurements and obtain consistent data. The research group identified three potential factors: pH, clay, and organic matter. Since clay and organic matter (OM) are highly correlated, they were grouped into one category. As a result, four samples that fit the categories of “high clay – high OM – high pH”, “high clay – high OM – low pH,” “low clay – low OM – high pH,” and “low clay – low OM – low pH” were used for comparison in this study.
In the experiments, incomplete dispersion was found in three of the replicates in the “high clay-high OM” category. It is highly likely that the clay content is limiting the reproducibility in dispersion. We also observed soil sticking on the wall of the 250-mL bottles during shaking, which may be improved by switching to smaller bottles that still allow enough room for dispersion in future experiments. We also found the reproducibility of measurement of POM was lower than particle size distribution due to the small mass of POM.
Duration: 12/11/2019
Principal Investigator(s): Michael L. Thompson