Thesis
Physical characteristics and agronomic impacts of winter wheat (Triticum aestivum L.) root restrictive soils in the Palouse
Washington State University
Master of Science (MS), Washington State University
05/2019
DOI:
https://doi.org/10.7273/000004002
Handle:
https://hdl.handle.net/2376/123793
Abstract
Exposed compacted subsoils pose a risk to sustained dryland winter wheat (Triticum aestivum L.) production in the in the Palouse agricultural region. Compacted, high bulk density soils can restrict root density in subsoils thereby decreasing crop water and nitrogen uptake and reducing crop performance. Root restriction and its effects on winter wheat agronomics were examined over the course of two field-scale on-farm studies in eastern Washington and northern Idaho. The first study aimed to understand: current within-field spatial variability of root restrictive depth (RRD), soil bulk density effects on root restriction, and root restriction effects on crop water uptake. At harvest in 2018, soil profiles in two fields were sampled to 120 cm depth at 15 cm increments were collected to measure soil bulk density, root density, and crop water use at depth. Results showed that within-field RRD varied (>120 - 75 cm), root density decreased with increasing bulk density, and soil water content at harvest increased as root density decreased. The second study evaluated the effect of subsoil compaction and water uptake on crop agronomics and nitrogen (N) use in eight site-years from 2016-2018. Soil samples from 0-120 cm depth and associated plant samples were collected at harvest to measure soil bulk density, N and water use, crop yield, and grain protein concentration. The yield gap between potential and realized yield was calculated from water in the top 120 cm of the soil profile after harvest. Results showed that compaction in the top 75 cm of the soil profile negatively affected grain and biomass yield by reducing crop extraction of deep soil water. Mean yield gaps for each field were high (352-1775 kg ha-1). Assuming that university fertilizer recommendations were used (0.045 kg N per kg yield goal), 15-76 kg N ha-1 was unused by the crop due to the yield gap. This assumption is consistent with our observations in 2018 where profile water content and residual nitrate-N in the subsoil were positively correlated. Tools are needed to help identify and adjust yield goals for root restriction to prevent over-application of N in affected field areas.
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Details
- Title
- Physical characteristics and agronomic impacts of winter wheat (Triticum aestivum L.) root restrictive soils in the Palouse
- Creators
- Rachel Sarah Breslauer
- Contributors
- HAIYING TAO (Advisor) - Washington State University, Department of Crop and Soil Sciences
- Awarding Institution
- Washington State University
- Academic Unit
- Department of Crop and Soil Sciences
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Identifiers
- 99900890797001842
- Language
- English
- Resource Type
- Thesis