Researching legume nitrogen fixation module
Soil measurements
Soil measurements
Soils from the plow layer are collected from each field plot. Some of this soil is analyzed immediately for the more biologically-active N pools and some of the soil is air-dried and analyzed later.
Measurements of soil N using fresh soil:
- available inorganic N (NO3- and NH4+)
- potentially available N (incubation of soil followed by the extraction of NH4+ to see how much new NH4+ is produced from organic matter mineralization by microbes in a week)
- microbial biomass (a relatively available source of N)
Measurements of soil N using dried soil:
- total soil carbon and N (similar to a measure of soil organic matter)
- particulate organic matter (POM-- a pool of soil organic matter that has not been fully decomposed and is slowly available). POM is considered to be an “active” soil organic matter fraction.
These different measurements provide information about different types of N that vary from being immediately available for plant uptake (such as inorganic N), to being slowly available for plant uptake after microbial decomposition (such as particulate organic matter N), to being almost unavailable for plant uptake (most of the total N in the soil has already been through extensive decomposition and can stay in the soil for hundreds of years).
In addition, the following tests were conducted to see if differences in soil texture or the availability of nutrients other than N influence soybean N fixation:
- soil texture analysis
- basic soil nutrient tests by the Cornell Nutrient Analysis Laboratory
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