Abstract
Core Ideas We hypothesized that plant exudates gel soil particles and on drying enhance water repellency. This has been carried out using rhizosphere‐scale mechanical and hydraulic measurements. Plant exudates enhanced soil hardness and modulus of elasticity as chia seed > maize root > barley root. Plant exudates caused measureable decreases in soil wetting rates through water repellency. Using rhizosphere‐scale physical measurements, we tested the hypothesis that plant exudates gel together soil particles and, on drying, enhance soil water repellency. Barley (Hordeum vulgare L. cv. Optic) and maize (Zea mays L. cv. Freya) root exudates were compared with chia (Salvia hispanica L.) seed exudate, a commonly used root exudate analog. Sandy loam and clay loam soils were treated with root exudates at 0.46 and 4.6 mg exudate g−1 dry soil and chia seed exudate at 0.046, 0.46, 0.92, 2.3 and 4.6 mg exudate g−1 dry soil. Soil hardness and modulus of elasticity were measured at −10 kPa matric potential using a 3‐mm‐diameter spherical indenter. The water sorptivity and repellency index of air‐dry soil were measured using a miniaturized infiltrometer device with a 1‐mm tip radius. Soil hardness increased by 28% for barley root exudate, 62% for maize root exudate, and 86% for chia seed exudate at 4.6 mg g−1 concentration in the sandy loam soil. For the clay loam soil, root exudates did not affect soil hardness, whereas chia seed exudate increased soil hardness by 48% at 4.6 mg g−1 concentration. Soil water repellency increased by 48% for chia seed exudate and 23% for maize root exudate but not for barley root exudate at 4.6 mg g−1 concentration in the sandy loam soil. For the clay loam soil, chia seed exudate increased water repellency by 45%, whereas root exudates did not affect water repellency at 4.6 mg g−1 concentration. Water sorptivity and repellency were both correlated with hardness, presumably due to the combined influence of exudates on the hydrological and mechanical properties of the soils.
Highlights
Soil water repellency increased by 48% for chia seed exudate and 23% for maize root exudate but not for barley root exudate at 4.6 mg g−1 concentration in the sandy loam soil
Water sorptivity was reduced by 30% for the sandy loam soil and 37% for the clay loam soil treated with chia seed exudate at the 4.6 mg g−1 concentration (Fig. 6)
Water repellency was increased by 48% for the sandy loam soil and 46% for the clay loam soil treated with chia seed exudate at a concen
Summary
Citation for published version (APA): Naveed, M., Brown, L. The sharp tip of a cone would result in considerable variability in measurements because it concentrates stress in a very small area (Zhang and Li, 2014), which in soil could be a few interacting particles We used these rhizosphere-scale mechanical and hydrological tests to measure soil mechanical stability, soil water sorptivity, and water repellency index influenced by barley and maize root exudates. We advance the earlier research of Hallett et al (2003), and other research exploring the water repellency of exudate-amended soils (e.g., Peng et al, 2011), by amending soils with controlled amounts of real root exudates These data are combined with small-scale mechanical characteristics, providing a robust assessment of small-scale testing approaches for deployment in direct measurements of rhizosphere soil. These combined data will improve our understanding of rhizosphere development and function and allow the interdependence of mechanical and hydraulic properties of the rhizosphere to be assessed
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