Major Soil Health Quality Indicators
Phospholipids are an essential structural component of all microbial cell membranes, including those found in soil. Unlike DNA, which can be present in living or dead cells, phospholipids are only present in living soil microbes. Phospholipid fatty acids (PLFAs) are the main structural component of the phospholipid molecule and can serve as useful biomarkers to determine the living microbial types and abundance in the soil (e.g. branched chain fatty acids are a biomarker for Gram-positive bacteria).
Neutral lipids (mainly in the form of triglycerides) are an essential energy storage component of Eukaryotic organisms. Neutral lipid fatty acids (NLFAs) are the main structural component of the neutral lipid molecule and in microbial community analysis, NLFAs are used to measure the abundance of Arbuscular Mycorrhizal Fungi (AMF), the most widespread symbiont fungus, involved with 85% of land plants and many important crops.
Soil lipid analysis is a widely-adopted technology for soil microbial community analysis and plant productivity studies. PLFA & NLFA analysis does not require culturing, and one can measure the "living" biomass, broad microbial community structure, and environmental stress impacts in near real-time. As a result, researchers can rapidly measure the impact of different inputs on soil health.
The US Department of Agriculture, National Resources Conservation Service (USDA/NRCS) now recommends the use of PLFA analysis as a key measure of soil health - USDA/NRCS Soil Health Technical Note # 450-03
However, before the soil lipids can be analyzed, one has to perform a long extraction process to isolate the phospholipid and neutral lipid fractions from the other plant and animal lipids present in the soil, and isolate the fatty acids from those respective lipid fractions.