Author
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Unger, Paul |
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Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/2/1997 Publication Date: N/A Citation: N/A Interpretive Summary: Soil organic matter contents (OMCs) decline when semiarid grasslands are brought under cultivation. This may cause soil aggregate size and stability to decline. Such declines, along with decreases in OMCs, may cause soils to become degraded and less suitable for producing crops. In this study, effects of cropping systems, crop or field conditions, and tillage methods on the size and stability of dry and water-stable aggregates and on OMCs of a Torrertic Paleustoll (Pullman clay loam) were determined. Samples for the study were obtained from the 0-3 cm depth in plots of four dryland studies and three nonreplicated field areas. The areas sampled ranged from those cropped to winter wheat and grain sorghum for over 20 years to grasslands that were brought under cultivation in 1994. In general, soil aggregates were smaller and OMCs were greater with no-tillage (NT) than with stubble mulch tillage (SMT) on areas cropped for over 20 years. On areas brought under cultivation in 1994, aggregates wer larger and OMCs were greater with NT than with other tillage methods. Dry aggregates in the 0.42-0.84 mm and 0.84-2.0 mm size ranges were among those most stable when sieved in water. The results of this study indicate that practices causing soil OMCs to remain higher and causing formation of dry aggregates in the 0.42-2.0 mm size range are important for keeping Torrertic Paleustolls such as Pullman clay loam and similar soils suitable for producing crops. Technical Abstract: Soil organic matter contents (OMCs) decline when semiarid grasslands are brought under cultivation. As a result, soil aggregate size and stability may decline, which, with the decreases in OMC, may degrade soil quality and reduce crop yields. Effects of cropping systems, crop or field conditions, and tillage methods on dry and water-stable aggregation and OMCs of a Torrertic Paleustoll (Pullman clay loam) were determined. Samples were obtained from the 0-3 cm depth in plots of four dryland studies and three nonreplicated field areas. Areas sampled ranged from those cropped to winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] for over 20 years to grasslands converted to cropland in 1994. In general, soil aggregates were smaller and OMCs were greater with no-tillage (NT) than with stubble mulch tillage (SMT) on areas cropped for over 20 yr. On areas recently converted to cropland, aggregates were larger and OMCs were greater with NT than with other tillage methods. The 0.42-0.84 and 0.84-2.0 mm dry aggregates were among those most stable when sieved in water. The results indicate practices that maintain soil OMCs at the higher levels and promote development of dry aggregates in the 0.42-2.0 mm size range are important for production sustainability of Torrertic Paleustolls such as Pullman clay loam and similar soils. |
