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Soil textural control over decomposition and soil organic matter dynamics




Scott, Neal A., author
Cole, C. Vernon, advisor
Sanford, R. L., Jr., committee member
Elliott, E. T., committee member
Peterson, G. A., committee member

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Soil texture is an important factor that influences litter decomposition and soil organic matter (SOM) dynamics, but few experiments have addressed specific mechanisms. Even less work has been done to answer the question of how important abiotic driving variables interact with soil texture to affect decomposition. I used laboratory soil incubations coupled with a simulation model to describe the interaction of soil texture with soil water availability and nutrient availability. I also addressed the importance of litter placement (surface vs. incorporated) across a gradient of texture, moisture and nutrient availability. The laboratory experiment was a randomized complete block design. Treatments consisted of texture (73%, 55%, 40% sand), water availability (- 0.012 MPa, -0.033 MPa and -0.3 MPa), nutrient availability (plus nitrogen (100 mg kg-1) and phosphorus (40 mg kg-1), ambient soil levels), litter placement (surface and incorporated), and replicates (3). Soils were packed into cores at a bulk density of 1.45. Wheat litter (C/N = 19) labeled with 14C was added to the soil cores at a rate approximating 2200 kg ha-1 total C addition being 2170 mg C kg-1. The cores were incubated for 90 d. Respiration (14C/12C-CO2) was measured weekly except during the first 10 d, when it was measured every 5 d. The fine textured soil lost more 14CO2 and 12CO2 than either of the other soils when litter was incorporated. Soil water potential significantly affected litter decomposition, the -0.012 MPa treatment decomposing faster than either the -0.033 or -0.3 MPa treatment, both of which were similar. Nutrient addition had no effect on decomposition for either litter placement treatment. Litter placement had no effect on the rate of decomposition. When the respiration data were divided into 3 time periods (0-10, 11-51 and 52-90 d), there was greater loss of surface 14CO2 from the coarse soil during 0-10 d (surface litter only). The overall 90 d effect of texture was not significant. Respiration rates correlated significantly to percent water-filled pore space (%WFPS) regardless of litter placement, although incorporated litter showed much less variability than did surface litter. Addition of litter carbon stimulated the mineralization of soil organic C, contributing significantly to the overall respiration rates during the incubation. Nutrient interactions may play an important role in decomposition and organic matter d3mamics, though they appeared unimportant in this experiment. A simulation model was constructed to analyze possible interactions between carbon, nitrogen and phosphorus during decomposition. Percent water-filled pore space controlled the utilization rate of litter C and SOM. Microbial C/N ratio controlled uptake rates of all C pools. Simulated results using high C/N ratio substrates showed slower decomposition than laboratory data, leading me to suspect that the simulated division of plant C into structural and metabolic C was incorrect. The model provided the opportunity to test ideas about the effect of texture and soil water potential on decomposition and SOM dynamics across a range of abiotic conditions and litter types.


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Soil texture
Soil dynamics
Microbial ecology
Soil microbiology


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