Carbon concentration predicts soil contamination of plant residues

Authors: Franzluebbers, Alan

Submitted to: Agricultural and Environmental Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/22/2020
Publication Date: 11/23/2020
Citation: Franzluebbers, A.J. 2020. Carbon concentration predicts soil contamination of plant residues. Agricultural and Environmental Letters. 5, Article 20037.

Interpretive Summary: Conservation agricultural systems promote surface residue cover of the soil. Estimating the mass of surface residues is complicated by contamination with soil. A scientist from USDA-Agricultural Research Service in Raleigh NC developed an estimation procedure based on routine analysis of samples for carbon concentration. The ash fraction of surface residues and pasture forage biomass was highly negatively associated with carbon concentration of samples. Therefore, as carbon concentration declines below a theoretical level of 45%, great likelihood exists that the sample is contaminated with soil. The equation developed had very low deviation, suggesting that carbon concentration alone would be an effective method to replace the additional analysis of ash fraction. These results will be particularly useful for soil and plant scientists studying agricultural systems with conservation management approaches and should lead to better scientific understanding of how management impacts soil and environmental quality.

Technical Abstract: Dry matter estimations of field-harvested plant materials can be complicated by varying soil contamination. A quick and simple method of screening materials for potential soil contamination would avoid unnecessary analyses. Harvested forage biomass and soil-surface crop residues were collected from cool-season perennial pastures, a silvopasture, and no-tillage cropland to determine ash fraction. Samples were also analyzed for total C and N concentration as part of routine plant analysis. When assessing ash fraction and C concentration along a gradient of soil contamination among 260 samples, a common regression was developed that had <1% coefficient of variation [Ash (kg/kg) = 1.01 - 0.0019 C (g/kg, r2=0.99, p<0.001]. This association was consistent with available data in the literature, which also showed a negative relationship between ash fraction and C concentration of organically-derived materials. Soil contamination of plant biomass and surface residues can be effectively estimated with this regression approach.