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Nitrogen fertilization and long-term no tillage impacts on soil properties and deep soil C storage under irrigation

Informally Refereed

Abstract

The net soil greenhouse gas mitigation potential of conservation agricultural management practices is strongly influenced by the direction and magnitude of soil organic C (SOC) change in deep soil layers (>6"). Deep SOC is typically old, highly processed, and consists of microbial products and root exudates associated with clay and other minerals. However, it can be susceptible to decomposition and priming from the addition of new, labile organic C. We examined long-term soil C dynamics (organic and inorganic) 13 years after conversion to no-tillage (NT) under varying nitrogen fertilizer rates (0 or 220 lbs a-1). We present preliminary data from throughout the soil profile (0-4') of δ13C of SOC and SIC, 14C, and organic and inorganic chemical composition by FTIR. Although there was surface (0-3") accumulation of new, corn-derived-C, it was lost from the deeper soils (>3"). Nitrogen fertilizer had little effect on SOC and SIC except in the 0-3" layer. After NT adoption, deep soil C became older, from both δ13 SOC and 14C data. Soil inorganic C increased at the two deepest depths, which was confirmed by FTIR. The δ13SIC suggested disequilibrium of C sources with carbonate minerals after only 13 years. These results indicate that deep soil C (both organic and inorganic) is surprisingly dynamic and susceptible to loss, despite conservation management practices.

Citation

Stewart, C.E.; Manter, D.K.; Delgado, J.A.; Del Grosso, S.A.; Calderon, F.; Heckman, K.; Snell, K. 2020, Nitrogen fertilization and long-term no tillage impacts on soil properties and deep soil C storage under irrigation. In: Proceedings, 2020 Great Plains Soil Fertility Conference. Volume 18: 1-6.
https://www.fs.usda.gov/research/treesearch/65616