ARS | Publication request: Tillage effects on soil water redistribution and bare soil evaporation throughout a season

Submitted to: Soil & Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 29, 2010
Publication Date: October 4, 2010
Citation: Schwartz, R.C., Baumhardt, R.L., Evett, S.R. 2010. Tillage effects on soil water redistribution and bare soil evaporation throughout a season. Soil & Tillage Research. 110(2):221-229.

Interpretive Summary: Maintaining adequate residue in dryland cropping systems is often difficult in semiarid regions with low yield potential. Low amounts of crop residue can decrease infiltration rates and increase evaporation of stored precipitation. We evaluated the effects of sweep tillage (ST) compared with an untilled (UT) soil to improve our understanding of near surface soil water dynamics in the absence of residue. After tillage, soil water contents at 2 and 4 inches were lowest in ST plots, even following repeated precipitation events. Tillage increased infiltration of precipitation and evaporation. Increased absorption of radiant energy under ST was partly responsible for the increased evaporation rates compared with UT. Differences in soil water storage for a 3-month period were small (0.4 inches). However, greater soil water contents near the surface and lower evaporation rates under UT afford improved moisture conditions and a longer window of opportunity for dryland crop establishment.

Technical Abstract: Tillage-induced changes in soil properties are difficult to predict, yet can influence evaporation, infiltration, and how water is redistributed within the profile after precipitation. We evaluated the effects of sweep tillage (ST) on near surface soil water dynamics as compared with an untilled (UT) soil during a 7-month period. Plots were established in a fallow field devoid of residue under stubble-mulch tillage management on a clay loam soil. Soil water contents were monitored using time-domain reflectometry at 0.05 to 0.3 m and using a neutron moisture gauge to a depth of 2.3 m. Soil temperature and net radiation were also monitored. During a 114-day period from April through July, tillage with a sweep (0.07 to 0.1 m) significantly decreased net water storage above 0.3 m soil depth by an average of 12 mm (P = 0.002) as compared with UT plots. After tillage, soil water contents at 0.05 and 0.1 m were significantly (P < 0.05) lower in ST plots, even following repeated precipitation events. Water contents at soil depths greater than or equal to 0.2 m were not influenced by tillage. Cumulative 3-day evaporation following precipitation events averaged 3.1 mm greater under ST compared with UT (P < 0.014). After extended dry periods, evaporation rates were similar among both treatments (approximately 0.3 mm day**1) despite the greater near-surface water contents of UT plots. Although ST plots exhibited 19 mm greater cumulative evaporation from July through October, this was offset by 26 mm greater infiltration compared with UT. A more advanced surface crust development and greater initial water contents were likely responsible for lower cumulative infiltration of UT compared with ST plots. Immediately after tillage, cumulative daily net radiation averaged 22% greater for ST compared with UT surfaces and these differences diminished with time. Increased evaporation under tillage was likely a result of enhanced vapor flow near the surface and greater absorption of radiation by a tilled surface with reduced albedo.