SOIL COMPACTION IMPACT ON SOIL FUNCTIONS IN DRYLAND PRODUCTION SYSTEMS OF THE PACIFIC NORTHWEST

Diana L. Salguero Gaibor

doi:10.7273/000007190

Soil compaction in agriculture is often overlooked and rarely measured. Once compaction occurs, restoring soil functionality is challenging and costly, and it varies in effectiveness based on soil texture and cropping system. Remediation techniques, including mechanical loosening and crop rotations aimed at breaking compacted layers, lack consistent validation due to limited reliable measurement tools. Compaction has been shown to reduce yield, primarily by limiting water availability; however, these effects fluctuate with weather conditions. The below-ground impact of compaction on roots and soil properties remains poorly understood, especially in rain-fed systems. This study addresses these gaps by linking compaction to critical agricultural functions, including yield, root growth, and soil water storage. Additionally, we introduced a field-scale protocol (10-500 ha) for measuring and mapping compaction. Compacted soils generally had higher water content but showed a decline of up to 20 mm in water depletion at 0- 1.05 m depths. Increased compaction correlated with reduced root length density in wheat roots across all diameters (0.30-1.05 m), whereas in canola, responses were less consistent. Root length density, which was explained 9-42% by volumetric water content, showed stronger correlations at shallower depths, and reductions in root density were associated with a 0.14 Mg ha-1 yield decrease. High-traffic areas showed quality losses, with canola yield decreasing by 0.5 Mg ha-1 and wheat by 1.2 Mg ha-1, along with reduced canola oil content (-1.9%) and lower test weights in wheat (-0.78 lb bu-1). Compaction also raised grain protein content by 3.3% in canola and 1.1% in wheat. We implemented pedotransfer functions using penetrometer force, depth of insertion, and soil water content for bulk density predictions, alongside environmental and terrain variables from proximal and remote sensing. Models achieved RMSEs of 0.09-0.81 Mg m-3 for profile and spatial bulk density predictions, though driest site predictions were less accurate. Our mapping protocol offered insights but also revealed challenges in accounting for spatial variability, suggesting the need for enhanced sampling. As the first study to link compaction with yield quality reductions, we propose that future research include quality traits as additional indicators of compaction. Furthermore, the potential impact of reduced root growth and biomass on carbon sequestration requires exploration.

SOIL COMPACTION IMPACT ON SOIL FUNCTIONS IN DRYLAND PRODUCTION SYSTEMS OF THE PACIFIC NORTHWEST

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