The effects of soil compaction on wheat seedling root growth are specific to soil texture and soil moisture status

Soil structure is a crucial soil physical property that determines a soil's ability to support the growth and development of plants. Soil compaction modifies soil structure by reducing pore space between soil particles thereby leading to a denser soil fabric. This often limits root growth by increasing soil strength and penetration resistance requiring roots to increase the energy needed to elongate and explore deeper soil. Apart from soil compaction, soil moisture also plays an important role in determining how resistant soil is to root penetration. An understanding of how the synergy of both compaction and moisture content affect root growth is essential to improving plant productivity. We used wheat (Triticum aestivum) seedlings to investigate the differences in root architectural properties using X-ray Computed Tomography imaging under three different compaction levels (1.3, 1.5 and 1.7 Mg m- 3) maintained at two different water contents (100% and 70% of field capacity). This was performed on soils of two different textures, a sandy loam and a sandy clay loam. Soil compaction to 1.7 g cm-3 significantly reduced root length, volume and surface area compared to lower compaction levels. Increased soil compaction also resulted in increased root growth angle in the sandy clay loam. Compaction reduced gas diffusivity in both soils (as determined by modelling). Soil moisture on the other hand had a significant impact on average root diameter; plants grown at 100% of field capacity had a higher average root diameter than those at 70% field capacity. Compaction up to 1.7 Mg m- 3 adversely effected wheat root growth in both soil textures regardless of moisture content.