Methods and Materials
This experimental plot was established in 2004 at the Konza Prairie Biological Station (KPBS) near Manhattan, KS (39° 6'28.44"N, 96°36'31.28"W), having been previously utilized for agricultural production of winter wheat. Three tillage and cropping practices were established to determine varying effects upon soil systems, these being grain sorghum (Sorghum bicolor) under continuous tillage, and no-tillage systems. Big bluestem native grass (Andropogon gerardii) was planted after initial tillage. The plot is located on a silty clay loam classified as Fine, smectitic, mesic Aquertic Argiudolls.
Bulk soil was sampled using a spade to prevent compaction, at a depth of 0 to 5 centimeters, and 5 to 15 centimeters from the surface. However in this study, only the 0 to 5 cm depth was utilized. Samples were separated by cropping system, plot number and depth and left to air dry at an ambient room temperature. Partially air dried samples were sorted through a 6mm sieve to remove stones plant fragments and artificially compacted aggregates.
Soil was then processed through a wet sieving method as defined by Mikha and Rice (2004). Samples were left to soak for ten minutes, and then the machine was run for ten minutes, breaking soil down into water soluble aggregates. Three sieve mesh sizes were used, separating aggregates into classes of greater than 2000 um, 250-2000 um and 53-250 um. These water stable aggregates were then oven dried to remove excess moisture and prevent further breakdown.
15 grams of soil post-aggregate separation were taken per aggregate size, per sample. For most samples of No-till and Conventional till sorghum there was insufficient sample in the aggregate class size of greater than 2000 um. 50 grams of bulk soil from each test plot were also prepared for microbial incubation. Samples were then artificially brought to field capacity using the gravimetric soil moisture equation. 5.5 mL of water were added to the 15 grams of aggregate separated soil, and 18.5 mL of water were added to the 50 grams of bulk soil. Bulk soil was incubated in an Erlenmeyer flask which was sealed in a quart sized mason jar. Aggregated samples were sealed in 100 ml serum vials. All samples were incubated at 25 degrees C with samples taken at staggered time intervals. Gas samples were then inserted and analyzed through a SHIMADZU GC-8A Gas Chromatograph to determine the concentration of CO2 gas, by measuring the electrical current signature.