Soil Water Depletion and Water Use Efficiency of Wheat and Pea in Saskatchewan

Understanding the distribution of soil water and roots in soil profiles and their relationship to root water uptake (RWU) patterns is important for developing “water smart” rotations. In the semi-arid prairies, the introduction of pea into a rotation with cereals can help mitigate the influence of drought. Pea has the potential to alter soil water depletion patterns and overall soil water use efficiency as related to rooting systems and edaphic factors. The benefits of implementing a pea crop into a rotation has been mainly examined in small plot studies conducted on level, well-drained soils in the southwestern region of Saskatchewan in the Brown soil zone. However, there is limited research from other areas encompassing variable soil profile characteristics and moisture conditions typically found across farm field landscapes. As well, previous studies have examined rooting depth of pea and wheat crops, but few have related this to observed RWU patterns. To address this knowledge gap, the rooting depth, RWU patterns, water use efficiency (WUE), and the water footprint (WF) of wheat and pea grown in rotation over a two-year period was determined at five sites in south-central Saskatchewan. This study was conducted during the 2021 and 2022 growing seasons under drought conditions near Central Butte, SK, and Langham, SK. Four sites were established near Central Butte and one site was established near Langham Saskatchewan. These sites were selected to provide contrast in landscape position and soil properties. The soil water content and depletion were monitored for both wheat (2021) and pea (2022) crops using Time Domain Reflectometry (TDR) probes to a depth of 135 cm. The rooting depth along with hydrogen and oxygen stable isotope abundances in the crop and soil water from different depths were used to determine RWU patterns. In addition, a comparative analysis was completed to assess crop WUE and WF for all sites. The 2021 and 2022 field seasons had below average precipitation; between May and August, the Central Butte sites received a total precipitation of 11.8 cm and 13.6 cm and the Langham site received 12.6 cm and 16.5 cm, respectively. These values are low compared to the climatic normal of 22.9 cm for Central Butte and 21.2 cm for Langham (Government of Canada, 2010). These conditions provided a unique opportunity to monitor crop response relative to rooting depth, RWU, WUE, and WF in drought conditions. Across the five sites, the average rooting depth for pea and wheat grown in both years was 62 cm and 56 cm. The rooting depth of the wheat crop was reduced compared to previous studies indicating that deep root growth was impeded by drought conditions. Even though the crops had similar effective rooting depths, the wheat crop appeared to more effectively use the small proportion of its roots that were located at depth to access deep soil water in the latter stages of growth. In contrast, the pea crop did not effectively use its small percentage of deep roots for RWU, and instead obtained its moisture from shallow soil depths. It was also determined that rooting depth and RWU patterns were site-specific and greatly influenced by landscape and soil properties such as subsoil salinity and layers of gravel present in the profile. Sites with salinity and textural breaks had truncated rooting systems which resulted in the wheat crop having shallow RWU similar to the pea crop. The WUE of the pea in 2022 was 190 kg ha-1 cm-1 compared to the 142 kg ha-1 cm-1 for wheat in 2021. The wheat-pea rotation had greater WUE and a lower WF compared to the wheat-wheat rotation; however, there was no evident deep soil water recharge in either rotation, which was attributed to two successive years of drought. These results showed the benefits of pea in the improvement of WUE and WF in a rotation, but hydrological benefits were reduced under drought conditions.

Name thesis:degree_name

Master of Science (M.Sc.)

Level thesis:degree_level

Masters

Discipline thesis:degree_discipline

Soil Science

Grantor

University of Saskatchewan

Year dc:date.issued

2024

Author dc:creator

• Paquette, Anne

Advisors dc:contributor.advisor

• Schoenau, Jeff
• Si, Bing

Committee members dc:contributor.committeemember

• Knight , Diane
• Arcand, Melissa
• Liu, Kui

• Wheat, Pea, Rooting Depth, Root Water Uptake, Water Use Efficiency, Water Footprint

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/10388/15442

OAI identifier oai:identifier

oai:harvest.usask.ca:10388/15442