Submitted to: Soil Science Society of America Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/9/2006
Publication Date: 5/8/2007
Citation: Pikul Jr, J.L., Osborne, S.L., Ellsbury, M.M., Riedell, W.E. 2007. Particulate Organic Matter and Water Stable Aggregation of Soil Under Contrasting Management. Soil Science Society of America Journal. 71(3):766-776. 2007(May-June Issue). Interpretive Summary: Soil conservation or crop management practices that improve soil aggregate stability also help to retard soil loss by maintaining surface conditions resistant to erosion. Objectives of our work were to determine effect of cropping rotation and soil management on soil organic matter, components of soil organic matter, and water stable aggregation of soil near the surface. Measurements were made on soil collected from seven sites that represented contrasts between alternative and conventional management. Management included tillage, crop rotation, native grass pasture, and intensity of corn stover removal. Experiments on comparable soil located in close proximity provide a unique and valuable opportunity to compare divergent management strategies. Of the seven field sites, three were producer-managed fields and four were replicated randomized complete block experiments. Our results show significant differences in components of soil organic matter as a result of crop and soil management. Systems that used less tillage or more diverse rotations (alternative practices) had greater fine particulate organic matter than conventional tillage and monoculture (conventional practices). Because particulate organic matter has been shown to be a labile fraction of soil organic matter, we conclude that the soil environment under alternative management is either less conducive to microbial transformation of particulate organic matter, and/or highly conducive to new particulate organic matter deposition (for example, through plant root systems that remain undisturbed by tillage). Importantly, we show a relationship between fine particulate organic matter and water stable aggregation that was consistent over a broad spectrum of soil, soil management, and cropping practice; as fine particulate organic matter increased, water stable aggregation increased.
Technical Abstract: Soil organic matter (SOM) is important to soil function. Objectives of our work were to determine effect of cropping rotation and soil management on SOM, components of SOM, and water stable aggregation (WSA) of soil near the surface. Measurements were made on soil collected from seven sites that represented contrasts between alternative (ALT) and conventional (CON) management. Management included tillage, crop rotation, native grass pasture, and intensity of stover removal. At each site, approximately 10 kg of soil (top 5 cm) was collected from each replication. Soil was separated into six aggregate groups using a rotary sieve. Aggregate size ranges for groups 1-6 were: <0.4, 0.4-0.8, 0.8-2, 2-6, 6-19, and >19 mm. Mean weight diameter was calculated using dry aggregate size distribution. For each aggregate group, dry aggregate stability, WSA, soil carbon (SC), SOM, fine particulate organic matter (fPOM), and coarse particulate organic matter was measured. Components of SOM were not uniformly distributed among aggregate groups. Average SC (seven sites) was significantly greater under ALT (31.0 g/kg) compared with CON (22.3 g/kg). No tillage (an ALT management) increased fPOM:SOM by 19% and 37% compared to tillage after 4 and 10 yr of NT, respectively. A 5-yr diverse rotation (an ALT management) increased fPOM:SOM by 36% compared to monoculture. There was a significant, positive relationship (r square = 0.79) between WSA and fPOM:SOM. Diversity of rotation or reduction of tillage increased fPOM and WSA and this may curb soil loss by maintaining surface conditions resistant to erosion. GRACEnet Publication.