Wheat stubble height effects on soil water capture and retention during long fallow

Authors: SCHILLINGER, WILLIAM - Washington State University; Wuest, Stewart

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/31/2021
Publication Date: 8/10/2021
Citation: Schillinger, W.F., Wuest, S.B. 2021. Wheat stubble height effects on soil water capture and retention during long fallow. Agricultural Water Management. 256. Article 107117. https://doi.org/10.1016/j.agwat.2021.107117.
DOI: https://doi.org/10.1016/j.agwat.2021.107117

Interpretive Summary: A 4-year study was conducted in a dry Mediterranean region of the Inland Pacific Northwest USA (PNW) from 2016-2019 to measure effects of winter wheat (WW) (Triticum aestivum L.) stubble height on over-winter precipitation capture in the soil and subsequent water retention during ensuing dry summer months during 13-mo-long fallow (F) periods. Stubble-height treatments were:(i) tall (75 cm), (ii) medium (25 cm), and (iii) short (8 cm). No tillage was conducted during fallow. On average, tall- and medium-height stubble captured significantly more overwinter precipitation than short stubble during two winters with drifting snow. However, from mid-April until late August, the greatest water loss occurred with tall stubble, presumably because all stubble was standing and offered less soil shading from flat residue compared to the short and medium treatments. Mowing tall stubble in mid-June before the hot, dry summer did not improve soil water retention. Soil temperatures at 3, 7, 15, 25, and 40-cm depths throughout June-August were coolest with the short, mowed, medium, and tall stubble, respectively, with significant differences of >1 °C among treatments. Averaged over four years, the medium and tall treatments were equal for water retention in the 180-cm soil profile at the end of 13-mo fallow and were significantly greater than the short stubble. Short stubble was a disadvantage for overwinter precipitation capture but was equal or better than the other treatments for retaining soil water from April to late August presumably because this treatment had the most residue lying flat on the soil surface for shading. For combined soil water retention and farm management factors, medium-height WW stubble is the best option for farmers in the PNW drylands.

Technical Abstract: A 4-year study was conducted in a dry Mediterranean region of the Inland Pacific Northwest USA (PNW) from 2016-2019 to measure effects of winter wheat (WW) (Triticum aestivum L.) stubble height on over-winter precipitation capture in the soil and subsequent water retention during ensuing dry summer months during 13-mo-long fallow (F) periods. Stubble-height treatments were:(i) tall (75 cm), (ii) medium (25 cm), and (iii) short (8 cm). An additional treatment: (iv) mow tall stubble in mid-June was included in the final two years. No tillage was conducted during fallow. Soil water measurements were obtained at the beginning, middle, and end of fallow in 15-cm increments to a depth of 180 cm. Additionally, seed-zone water content was measured at the end of fallow in 2-cm increments to a depth of 26 cm. Near-surface soil temperature was measured from June-August. On average, tall- and medium-height stubble captured significantly more overwinter precipitation than short stubble. These over-winter water storage differences were particularly pronounced after two winters with drifting snow. However, from mid-April until late August, the greatest water loss occurred with tall stubble, presumably because all stubble was standing and offered less soil shading from flat residue compared to the short and medium treatments. Mowing tall stubble in mid-June before the hot, dry summer did not improve soil water retention. Soil temperatures at 3, 7, 15, 25, and 40-cm depths measured electronically throughout June-August were coolest with the short, mowed, medium, and tall stubble, respectively, with frequent significant differences of >1 °C among treatments. Averaged over four years, the medium and tall treatments were equal for water retention in the 180-cm profile at the end of 13-mo fallow and were significantly greater than the short stubble. Short stubble was a disadvantage for overwinter precipitation capture but was equal or better than the other treatments for retaining soil water from April to late August; presumably because this treatment had the most residue lying flat on the soil surface for shading. For combined soil water retention and farm management factors, medium-height WW stubble is the best option for farmers in the PNW drylands.