|Ye, Rongzhong - Clemson University|
|Parajuli, Binaya - Clemson University|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/15/2019
Publication Date: 5/30/2019
Citation: Ye, R., Parajuli, B., Sigua, G.C. 2019. Subsurface clay soil application improved aggregate stability, nitrogen availability and organic carbon preservation in degraded Ultisols with cover crop mixtures. Soil Science Society of America Journal. https://doi.org/10.2136/sssaj2018.12.0496.
DOI: https://doi.org/10.2136/sssaj2018.12.0496 Interpretive Summary: Soil organic carbon (SOC) in the Coastal Plain soils of the southeastern United States (US) is inherently low mainly due to the warm and wet climate environment that enhances microbial decomposition. Extensive clay mineral weathering and clay eluviation further limit the soils’ capacity to stabilize SOC, however, can’t be fully addressed by current management practices of high residue return and conservation tillage. Innovative management strategies are therefore required to stabilize SOC and improve soil fertility and productivity. In the present study, we demonstrated that applications of "in-situ" subsurface clay soils improved soil structure, nutrient availability, and the preservation of labile organic carbon (C), indicating its effectiveness in enhancing soil fertility and health of degraded Ultisols across the southeastern United States, where a quarter of US agricultural products is currently being produced. Reversing the loss of SOC is important to improve long-term soil health, productivity, and sustainability. We demonstrated that applications of "in situ" subsurface clay soils increased soil clay contents promoting the formation of macroaggregates. Such application did not affect microbial community structure and composition, but suppressed enzymatic activities resulting in low C turnover rates and the preservation of labile organic C. Clay soil additions increased the fixation of ammonium (NH4+), while reduced nitrate (NO3-) leaching substantially, leading to higher N availability. Our results further suggest that subsurface clay soil amendment may be an effective soil management strategy to improve soil structure, soil fertility, and SOC content in the degraded sandy Coastal Plain soils. However, more research on its long-term effects on soil processes and crop productivity is still needed.
Technical Abstract: Coastal Plain soils of southeastern United States are highly degraded with low soil organic carbon (SOC), meager soil fertility, and poor soil structure. We tested the effectiveness of clay soil amendment to promote the formation of soil aggregates, improve organic C stability, and enhance nutrient availability in the field. Subsurface clay soils (B horizon, 25 percent, % clay) were applied (~25 tons per hectare, t/ha) on the soil surface followed by planting winter cover crop mixtures. Crop growth, nutrient uptake, and other relevant soil biogeochemical properties were analyzed at the end of winter season. Additions of subsurface clay soils enhanced the formation of water-stable macroaggregates (250-2000 micrometer, um) from 32% to 54% and increased mean weight diameter of the aggregates from 390 to 592 um. Additions of subsurface clay soils also increased clay content from 1.5% to 3.8%, but did not change soil texture, pH, water holding capacity, and bulk density. The concentration of dissolved organic nitrogen was not affected by clay amendment while nitrate (NO3-) leaching from field was reduced by 61% because of clay soil application. However, clay soil additions inhibited the activities of C- (N-acetyl-beta-glucosaminidase, beta-D-cellubiosidase, beta-glucosidase, and beta-xylosidase) and N-cycling (leucine aminopeptidase) enzymes. Moreover, application of clay does not modify soil microbial community level substrate utilization patterns resulting in 63% reduction in C turnover rate and 19% increase in concentrations of labile organic carbon C. Our results indicated that subsurface clay soil amendment can improve soil structure, nutrient availability, and the stability of labile C in the field, at least in a short term, are critical in enhancing the productivity and sustainability of the degraded Coastal plain soils.