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Title: Soil aggregates and their associated carbon and nitrogen content in winter annual pastures using different tillage management options

Author
item ANDERS, M - University Of Arkansas
item BECK, PAUL - University Of Arkansas
item WATKINS, B - University Of Arkansas
item Gunter, Stacey
item LUSBY, KEITH - University Of Arkansas
item HUBBELL, D - University Of Arkansas

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2010
Publication Date: 6/2/2010
Citation: Anders, M.M., Beck, P.A., Watkins, B.K., Gunter, S.A., Lusby, K.S., Hubbell, D.S. 2010. Soil aggregates and their associated carbon and nitrogen content in winter annual pastures using different tillage management options. Soil Science Society of America Journal. 74:1339-1347.

Interpretive Summary: Winter annual pastures are normally established on areas that are more steeply sloped and not deemed suitable for row-crop production. Using conventional tillage methods to prepare these fragile lands for winter annual pastures leads to increased erosion and rapid soil degradation. The objectives of this study were to determine the effects of tillage intensity, by soil depth and landscape position, on water-stable soil aggregates, their subsequent carbon and nitrogen content, and soil bulk density. The study consisted of three tillage treatments, conventional-tillage, disk-tillage, and no-tillage, imposed on fields managed using conventional tillage for 6 years before the study. Data were collected after 3 years of consistent treatment management with soil samples grouped by their landscape position (summit, side-slope, or toe-slope). Water-stable aggregates were determined by wet sieving, and total water-stable aggregates were significantly influenced by tillage and soil depth but not by landscape position. Total water-stable aggregates were greater in the first 5 cm of soil compared to the second in the disk-tillage and no-tillage treatments, but were similar in the conventional-tillage soils. Mean water-stable aggregates in the 4 largest aggregate sizes were greatest in the first 5 cm of soil, but there was no difference between sample depths in the smaller sizes of aggregates. For all tillage treatments and soil depths, mean water-stable aggregates decreased from the larger sizes to the next smaller size and increased thereafter as aggregate size decreased. Carbon and nitrogen content in water-stable aggregates was greater in the first 5 of cm soil than in the second, regardless of tillage treatment or landscape position. Soil bulk density was unaffected by tillage treatment. Hence, winter annual grass production using disk-tillage or no-tillage practices is a viable means of maintaining or enhancing soil quality.

Technical Abstract: Traditionally, winter annual pastures are established on grazing areas that are steeply sloping and not regarded as suitable for row-crop production. Using conventional (CT) tillage methods to prepare these fragile lands for winter annual pastures leads to increased erosion and rapid soil degradation. The objectives of this study were to determine the effects of tillage intensity, by soil depth and landscape position, on water-stable soil aggregates (WSA), their subsequent carbon (C) and nitrogen (N) content, soil bulk density (BD), and the C and N contribution to the soil via WSA. The study consisted of three tillage treatments (CT, disk-tillage (DT), and no-tillage (NT)) imposed on fields managed using CT for 6 years before the study initiation. Data were collected after 3 years of consistent treatment management with soil samples slope. Five size classes of WSA were determined by wet sieving. Total WSA content was significantly influenced by tillage and soil depth but not by landscape position. Total WSA were greater in the 0 to 5-cm soil layer compared to the 5 to 10-cm layer in the DT and NT treatments but similar in the CT soil layers. Mean WSA (pooled over tillage and landscape position) in the 4 largest aggregate size classes were greatest in the 0 to 5-cm soil layer but there was no difference between sample depths in the smallest size class (0.5 to 0.25-mm). As aggregate size class decreased, the relative content of aggregates at the toe-slope landscape position increased. For all tillage treatments and soil depths, mean WSA (pooled over tillage and landscape position) decreased from the largest size class (> 4 mm) to the next size class (4 to 2-mm) and increased thereafter as aggregate size decreased. Carbon and N content in WSA was greater in the 0 to 5-cm soil layer than in the 5 to 10-cm layer regardless of tillage treatment or landscape position. Soil BD was unaffected by tillage treatment. Water-stable aggregate C and N content was equally enhanced in the DT and NT treatments, with both being greater than the CT treatment. Water-stable aggregate C and N weights were greater in the DT and NT treatment 0 to 5-cm soil layer where differences in sample depth within WSA size class decreased as WSA size decreased. Winter annual grass production using DT or NT practices is a viable means of maintaining or enhancing soil quality.