Greenhouse growth bioassay confirms soil nitrogen availability indicated by the flush of CO2

Authors: PEHIM LIMBU, SMRITI - Johns Hopkins University; Franzluebbers, Alan

Submitted to: Biology and Fertility of Soils
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/3/2021
Publication Date: 3/23/2022
Citation: Pehim Limbu, S., Franzluebbers, A.J. 2022. Greenhouse growth bioassay confirms soil nitrogen availability indicated by the flush of CO2. Biology and Fertility of Soils. 58:91-103. https://doi.org/10.1007/s00374-021-01614-9.
DOI: https://doi.org/10.1007/s00374-021-01614-9

Interpretive Summary: Soil testing for nitrogen availability in pasture systems would benefit from a rapid and reliable indicator to assess nitrogen availability. Scientists from USDA-ARS in Raleigh NC and John Hopkins University (formerly at North Carolina State University) evaluated the plant growth responses of a test crop planted in unamended soils collected from 55 pastures throughout North Carolina and Virginia. Plant dry matter and nitrogen uptake of the test crop during six weeks of growth in the greenhouse was highly related to several organic carbon and nitrogen fractions. However, a simple, rapid, and reliable indicator based on simple microbial activity (the flush of carbon dioxide) was best associated with plant growth responses. Low cost and short time required for this simple indicator make it suitable for soil testing, and because it was robust in predicting plant growth. The strong association of the flush of carbon dioxide with plant nitrogen uptake under semi-controlled greenhouse conditions corroborated use of the assay as a rapid and reliable indicator of soil nitrogen availability. These results will be valuable for farmers wanting to make efficient applications of nitrogen to enhance profit and steward natural resources.

Technical Abstract: Estimating soil nitrogen (N) availability from inorganic and organic N fractions is important for developing effective N fertilizer recommendations for plant growth. We examined the ability of various soil biological characteristics, including the flush of CO2, to predict soil N availability and subsequent plant dry matter production and N uptake in semi-controlled greenhouse experiments. Soils were collected from the 0-10-cm depth of 57 tall fescue [Schedonorus arundinaceus (Schreb.) Dumort.] fields mostly in North Carolina and Virginia. Several soil biological properties, including the flush of CO2, were positively correlated with net N mineralization, and with plant dry matter and N uptake during six-week greenhouse growth of sorghum-sudangrass (Sorghum bicolor (L.) Moench ssp. Drummondii). Some physical and chemical soil properties added minor contributions to the explanation of this variation in soil N supply and greenhouse growth. Additionally, the flush of CO2 was reflective of management history and soil texture. We conclude that the flush of CO2 is a reliable predictor of soil N availability across a diversity of soils under pasture management.