|Camp Jr, Carl|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/1999
Publication Date: N/A
Interpretive Summary: In some southeastern Coastal Plain soils, dense soil layers restrict plant roots from growing into deeper soil layers where additional water and nutrients may be stored. Annual deep tillage is often used to break up the dense layer and allow roots to grow deeper. If the dense layer is kept wet and soft, roots are more likely to grow through it. Burying drip irrigation tubes near the dense layer may allow irrigation to keep the dense layer moist and reduce the need for deep tillage. Cotton, soybean, and wheat were grown for two years in an experiment where no tillage was used. Treatments included drip irrigation tubes buried 30 cm deep (same depth as dense soil layer), spaced either 1 m or 2 m apart, and irrigation applied at three rates. Irrigation increased crop yield only for soybean in one year. There were no differences in yield for the two tube spacings or three irrigation rates. Root observations and soil strength measurements during the growing season indicated that a dense layer formed at a much shallower depth than usual (<5 cm) because no tillage was used. This shallow dense layer was not wetted by irrigation and prevented roots from growing into the irrigated soil area, which removed any possible beneficial effect of irrigation on crop growth and yield. Hence, strategies must be developed to remove the effects of shallow, dense soil layers before the benefits of subsurface drip irrigation can be realized.
Technical Abstract: Subsurface drip irrigation may replace the need for deep tillage in conservation tillage by keeping compacted soil layers moist enough for root growth. A two-year experiment that included wheat, soybean, and cotton was conducted with subsurface drip irrigation. The irrigation system had been used for five years before this experiment and provided two irrigation ndrip line spacings (1 m and 2 m) and three irrigation amounts (6, 9, and 1 mm/application). Irrigated soybean yields were greater than rainfed in one of the two years. No differences in yield occurred among irrigation drip line spacing or irrigation depths. Also, neither cotton nor wheat yields were increased by irrigation. Observations during the growing seasons, cotton root observations after harvest, and soil strength measurements during the spring indicate that considerable soil compaction occurred at very shallow soil depths (< 5 cm) and restricted root growth. This compaction probably limited the efficacy of subsurface drip irrigation, which was located at the 30-cm depth. Based on these results, it appears that strategies must be developed to reduce soil strength to obtain optimum no-tillage crop production with subsurface drip irrigation on these soils.