Submitted to: Journal of Soil Biology and Biochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/1996
Publication Date: N/A
Interpretive Summary: Knowledge of soil organic matter turnover is important for understanding C sequestration, nutrient cycling, and biophysical attributes of land management systems within particular ecological and climatic regions. Quantitative relationships between active soil organic matter pools and soil texture are lacking and limit the predictability of soil organic matter dynamics within regions having differences in soil texture, such as the warm, sub-humid to humid agroecological zone in central and eastern Texas. Clay soils had more microbial biomass than sandy soils, however the activity of this microbial biomass was less in clay soils than in sandy soils. Our results imply that land management practices that favor soil organic matter accretion (i.e., conservation tillage, intensive cropping with residue returned to the soil, grain-forage rotations, and integrated animal-grain systems) will provide plant-available nutrients more rapidly in sandy than in clay soils. Land management influences on soil, water, and air quality will be more precisely defined with the knowledge of these relationships between active pools of organic matter.
Technical Abstract: Turnover of C and N through the active fractions of soil organic matter can be affected by soil texture. Relationships between soil organic C (SOC), soil microbial biomass C (SMBC), mineralizable C and N during a 21 d incubation, and basal soil respiration (BSR) were evaluated on eight soil types from Texas that varied in soil texture (7 to 45% clay) and organic matter. The portion of SOC as SMBC increased with increasing clay content, whereas the relationships of mineralizable C and N and BSR to SOC were not affected by soil texture. The ratio of BSR-to-SOC averaged 1.4 mg mineralizable C/g SOC/d. The amount of mineralizable C and N and BSR per unit of SMBC, however, decreased with increasing clay content, indicating that the soil microbial biomass (SMB) was more active in coarse-textured soils than in fine-textured soils. The average specific respiratory activity was 29 and 11 mg mineralizable C/g SMBC/d with 10% and 40% clay, respectively. The C:N ratio of the mineralizable fraction averaged 10 and was not affected by soil texture. The established relationships between active SOC fractions and soil texture could be used in models predicting SOC turnover.