Use of Soil Protein Pools as Indicators of Soil Nitrogen Mineralization Potential

Abstract

Autoclaved‐citrate extractable (ACE) soil protein is included in some soil health assessments as a biological indicator. Furthermore, soil protein contents may be related to the ability of a soil to make nitrogen (N) available for plants by mineralization. The main objective of this study was to evaluate the correlation between ACE protein and potential net N mineralization in undisturbed soil cores from 57 fields in California under annual crops. Total N in the soils ranged from 0.65 to 12.5 g kg−1, and the sites represented eight Soil Taxonomy orders. Soil ACE protein concentrations ranged from 1.0 to 45.2 g kg−1 soil. Although the correlation between ACE protein and potential net N mineralization was positive, ACE protein explained only 21% of the variability in potential net N mineralization across all sites, which was less than total N. Under the assumption that proteins contain 16% N, ACE protein‐N accounted for 28% of total N across all sites. However, in some soils with a high total N content, ACE protein accounted for up to 67% of total N. Because autoclaving is expected to denature some proteins, these values seem very high and are likely caused by the interference of coextracted humic substances. Our results do not suggest that ACE protein is a better predictor of potential net N mineralization than total soil N, which may be at least partly due to an apparent interference of coextracted humic substances with the protein assay. Core Ideas ACE protein concentrations ranged from 1.0 to 45.2 g kg−1 soil. ACE protein and N mineralization were positively correlated (r = 0.46). The correlation was weaker than between N mineralization and total soil N. Co‐extracted humic substances appear to interfere with the protein assay.

An identified agronomic interpretation for potassium permanganate oxidizable carbon

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A soil health scoring framework for arable cropping systems in Saskatchewan, Canada

“…Nitrogen is a crucial element for both crop production and the soil ecosystem. Total N represents long-term N supply in the soil, whereas shorter-term N supply metrics can be gleaned from soil protein, potential minimizable N estimates (Geisseler et al 2019), or inorganic N (NO − 3 and NH þ 4 ). In our study, different N attributes were not only included to help capture N cycling from different angles but also to better understand which N metrics might be most useful in determining soil healthto that end, soil TN and protein estimates had the greatest weighting factors.…”

Dissolved organic carbon chemical composition controls the rate of CO2 release from rewetted soil

“…However Williams and Xia (2009) using multiple methods of characterization found no detectable levels of monomeric amino acids in rewetted soil, suggesting most osmolytes were retained within cells. Extractable proteinaceous material has been suggested as an indicator of soil nitrogen mineralization potential (Geisseler et al, 2019). Aromatics containing N, largely pyridinic-N and pyrrole compounds occur in soils (Gillespie et al, 2014), and are probably less labile than aliphatic N. Although we found the N-containing aliphatic fraction was largely depleted after 48 hours of incubation, the average empirical formula of the DOC remaining in solution still contained about half of the number of N atoms as the DOC originally in solution (Table 1), suggesting the possible presence of less-labile N-containing molecules.…”