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Title: Influence of residue and nitrogen fertilizer additions on carbon mineralization in soils with different texture and cropping histories

Author
item CHEN, XIANNI - UNIVERSITY OF ILLINOIS
item WANG, XUDONG - UNIVERSITY OF ILLINOIS
item LIEBMAN, MATT - IOWA STATE UNIVERSITY
item Cavigelli, Michel
item WANDER, MICHELLE - UNIVERSITY OF ILLINOIS

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2014
Publication Date: 7/31/2014
Citation: Chen, X., Wang, X., Liebman, M., Cavigelli, M.A., Wander, M. 2014. Influence of residue and nitrogen fertilizer additions on carbon mineralization in soils with different texture and cropping histories. PLoS One. 9:e103720. DOI: 10.1371/journal.pone.0103720.

Interpretive Summary: Storing carbon in agricultural soils can help reduce the atmospheric concentration of carbon dioxide, the dominant greenhouse gas. The amount, form, and recalcitrance to decomposition of soil carbon are influenced by agricultural management but also by soil type. The interaction between these two factors is not well studied. We showed, using soils from two long-term agricultural research sites with similar management treatments, one in Iowa and one in Maryland, that soil type, particularly clay charge, has a strong influence on soil carbon fractions. In the Iowa soil, which has a high clay charge, management history had very little impact on the amount, form and recalcitrance of soil carbon. In the Maryland soil, which has a relatively low clay charge, use of diversified rotations and manure increased labile and stable soil carbon forms by about 30% to 50% compared to more conventional farming practices. Adding wheat residues to incubated soils increased labile and stable soil carbon forms and decreased the decay rate of labile forms more in the Maryland than the Iowa soil. Overall, clay type and carbon saturation dominated the Iowa soil’s response to external inputs and made labile and stable fractions more vulnerable to decay. Trends in occluded particulate organic carbon suggest aggregate protection influences carbon dynamics in the low-activity Maryland soil. Clay charge and occluded particulate organic carbon content were better predictors of soil carbon dynamics than were percent clay or particulate organic carbon. This information will be useful to other scientists and eventually to policymakers interested in identifying best management practices for different soil types to augment storage of organic carbon in agricultural soils.

Technical Abstract: To improve our ability to predict SOC mineralization response to residue and N additions in soils with different inherent and dynamic organic matter properties, a 330-day incubation was conducted using soil sampled from two long-term experiments (clay loam Mollisols in Iowa [IAsoil] and silt loam Ultisols in Maryland [MDsoil]) comparing conventional grain systems (Conv) amended with inorganic fertilizers with 3yr (Med) and longer (Long), more diverse cropping systems amended with manure. A double exponential model was used to estimate the size (Ca, Cs) and decay rates (ka, ks) of active and slow C pools; we compared these with total particulate organic matter (POM) and occluded-POM (OPOM). The high-SOC IAsoil containing high-activity smectite clays maintained smaller labile pools and higher decay rates than the low-SOC MDsoil containing semi-active kaolinitic clays. Net SOC loss was greater (2.6 gC•kg-1; 8.6%) from the IAsoil than the MDsoil (0.9 gC kg-1, 6.3%); fractions and coefficients suggest losses were principally from IAsoil’s resistant pool. Cropping history did not alter SOC pool size or decay rates in IAsoil where rotation-based differences in OPOM-C were small. In MDsoil, use of diversified rotations and manure increased ka by 32% and ks by 46% compared to Conv; differences mirrored POM- and OPOM-C contents. Residue addition prompted greater increases in Ca (340% vs 230%) and Cs (38% vs 21%) and decreases in ka (58% vs 9%) in the IAsoil than the MDsoil. Reduced losses of SOC from residue-amended MDsoil were associated with increased OPOM-C. Nitrogen addition dampened CO2-C release. Clay type and C saturation dominated the IAsoil’s response to external inputs and made labile and stable fractions more vulnerable to decay. Trends in OPOM suggest aggregate protection influences C dynamics in the low-activity MDsoil. Clay charge and OPOM-C content were better predictors of soil C dynamics than percent clay or POM-C.