|Pikul Jr, Joseph|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/30/2008
Publication Date: 1/21/2009
Citation: Pikul, Jr., J.L., Chilom, G., Rice, J., Eynard, A., Schumacher, T.E., Nichols, K., Johnson, J.M.F., Wright, S., Caesar, T., Ellsbury, M. 2009. Organic Matter and Water Stability of Field Aggregates Affected by Tillage in South Dakota. Soil Science Society of America Journal. 73:197-206. Interpretive Summary: Ten years of NT increased SOC in the top 50 mm by 9% compared with CT and the increase in SOC corresponded to marked differences in soil properties and quality of SOM. Soil under NT had a greater fPOM:SOM ratio compared with CT. We found that as the fPOM:SOM ratio increased, WSA increased. Average number of basidiomycete fungi (decomposers of cellulose and lignin in nonliving organic matter) increased 20% under NT compared with CT. We conclude that the soil environment under NT is highly conducive to particulate organic matter accumulation (through plant root systems that remain undisturbed by tillage) and thus the greater population of fungi under NT compared with CT. Differences in decomposition of organic material under these two tillage systems resulted in unique chemical constituents of SOM. There was a greater abundance of wax-type carbon in both whole soil and humin under NT compared with CT. Organic compounds may impart some degree of water repellency thereby improving WSA. Water stable aggregation was 60% greater under NT compared with CT. It is likely that the greater; 1) concentration of glomalin, 2) fungi population, and 3) abundance of wax-type C (associated with hydrophobicity) found under NT, compared with CT, contributed, in part, to greater DAWSA under NT compared with CT. In northern sub-humid regions of the Great Plains, wind and water erosion are persistent problems. Tillage practices that improve soil aggregate stability will also help to retard soil loss by maintaining surface conditions resistant to erosive forces.
Technical Abstract: Increased tillage intensity has been associated with declines in soil organic matter (SOM). A case study was conducted (2001-2004) on adjacent farms (both in a two-year crop rotation) in eastern South Dakota to quantify tillage effects on components of SOM and soil aggregate stability. One farm used no tillage (NT) and the other used chisel tillage (CT). A rotary sieve was used to separate surface soil (top 50 mm) into 6 aggregate groups, <0.4, 0.4-0.8, 0.8-2, 2-6, 6-19, and >19 mm. Dry aggregate water stable aggregation (DAWSA) was measured by wet-sieving. Soil organic carbon (SOC), nitrogen, glomalin and basidiomycete fungi were measured. Fine particulate soil organic matter (fPOM, 0.5-0.053 mm) and coarse POM (2.0-0.5 mm) were isolated by sieving. Quantitative solid-state C-13 nuclear magnetic resonance direct-polarization magic-angle spinning (DP MAS NMR) was used to determine C type in humic acid (HA), humin, and soil. Ten years of NT increased SOC in the top 50 mm by 9% compared with CT. Average fPOM was 37% greater (p=0.001) under NT compared with CT. Average SOC of aggregates was 32.3 g/kg under NT and 29.6 g/kg under CT. Average DAWSA was 63% greater (p=0.005) under NT compared with CT. Aggregate wettability was less (p=0.001) under NT compared with CT. Slower water uptake under NT might be attributed to greater abundance of wax-type C (soil and humin) under NT compared with CT. No tillage increased SOM and DAWSA, thus maintaining surface soil conditions resistant to erosion.