•Soil microbial biomass (MB) is recognized as the best indicator of soil quality, but laboratory tests for MB are $80 to $500, and results are not available for an average of 2 weeks, making them impractical tools for most growers.
•We developed microBIOMETER®, a 10 minute low cost assay for MB that analyzes results on a smart phone. The test accurately measures a soil sample and extracts a consistent fraction of the microbes from the soil particles. Extracted microbes are immobilized on a membrane and then quantified with the cell phone.
•The test correlates R2= 0.81 with PLFA and similarly with Carbon Fumigation: it does not correlate well with respiration. The CV of the assay is 10%.
•MB as measured by microBIOMETER® has been used for rapid evaluation of cover crop and amendment effectiveness, quality of compost and soil, carbon sequestration estimation, and discriminating between organic and chemically treated soil.
Microbial biomass (MB) is the best single indicator of soil health (Doran 2000) because it is low in any situation that is harmful to plant growth and vice versa, and because MB can predict success before plant outcome. In addition, MB correlates with other widely accepted soil health indicators, such as Nitrogen, Soil Organic Carbon (SOC), and pH.
Shown below are data extracted from Anderson et. al. 1989 comparing microbial biomass (MB) to other analyses.
Standard practices for measuring MB are error-prone, laborious, inconsistent and expensive.
Given the problems with established methods, we sought to develop a test that is:
•Simple to perform
•Free of hazardous chemicals
•Rapid (comparatively instantaneous)
•Less variable/ more consistent
1.Accurately and consistently measure soil by volume
2.Extract microbes from soil particles using agitation in a precisely formulated solution
3.Allow soil particles to settle, leaving microbes in suspension
4.Apply microbial suspension to a test card and analyze with a smartphone app
10 different samples each of 3 soils were analyzed on different days. CVs ranged from 3.1% to 11.8% for each group of 10 samples. The CVs across all three days were Soil 1 = 3.1%, Soil 2 = 9.1%, and Soil 3 = 6.9%.
One of the most difficult aspects of analyzing with smartphone cameras is differences in color temperature that users may image the testcard. The microBIOMETER® app controls for differences in color temperature and allows for consistent readings in all lighting conditions. Shown are 5 samples imaged in warm incandescent, fluorescent, direct sun, and shade. The CVs for the 5 samples across the 4 different lights were 10.6, 11.6, 7.5, 11.3, and 7.3%.
The microBIOMETER® is a valuable tool for researchers, growers, farmers, arborists, gardeners and landscapers. We designed the test by adhering to the following constraints:
The microBIOMETER® test has proved useful for evaluating: