Root Responses to Alterations in Macroporosity and Penetrability in a Silt Loam Soil. Issue 4 (30th June 2014)

• Record Type: Journal Article
• Authors: Hernandez-Ramirez, Guillermo; Lawrence-Smith, Erin J.; Sinton, Sarah M.; Tabley, Frank; Schwen, Andreas; Beare, Michael H.; Brown, Hamish E.
• Is Part Of: Soil Science Society of America Journal. Volume 78:Issue 4(2014)
• Page Start: 1392
• Page End: 1403
• Publication Date: 2014-06-30
• Subjects: Soils -- United States -- Periodicals; Soil science -- Periodicals; Periodicals; 631.4973
• DOI: 10.2136/sssaj2014.01.0005
• Languages: English
• ISSNs: 0361-5995

Abstract

Abstract : Changes in soil physical conditions can have an impact on plant root growth. However, the underlying functional responses of root growth to variations in soil physical properties still remain poorly understood. We assessed the responses of barley ( Hordeum vulgare L.) roots to a typical range of soil physical properties created by applying different degrees of loosening or compaction to subsurface soil layers. A replicated field experiment was established on a Templeton silt loam soil (Dystric Ustochrept) in Canterbury, New Zealand. Following removal of the top 15 cm of soil, five mechanical treatments were applied: loosened by cultivation, three degrees of compaction using a roller (one pass, eight passes, and eight passes with vibration), and an untreated control. Subsequently, the top 15 cm of soil was repositioned. The impact of these treatments on soil physical properties in the subsurface soil layer (15–30 cm) produced a discernible gradient that was well characterized by shifts in pore‐size distribution, in particular macroporosity (radii > 30 μm). Macroporosity values were well represented throughout the range from 0.035 up to 0.20 m 3 m −3 ( n = 50), and these values were negatively correlated with both penetration resistance and bulk density measurements ( r ≤ −0.80; P < 0.001). We found clear responses of root growth to this established gradient. As macroporosity decreased, root diameter increased by 42% ( r = −0.63), while root length density decreased by 65% ( r = +0.66). However, these divergent responses of root diameter and length density to changes in macroporosity were not linear over the whole range but exhibited specific response thresholds. The thresholds of macroporosity, where root responses inflected and became particularly pronounced, were <0.077 m 3 m −3 for root diameter and >0.12 m 3 m −3 for root length density, suggesting that macroporosity values above 0.13 m 3 m −3 can facilitate root growth. Although these belowground responses were clearly evident, we detected no effects of these varying conditions on aboveground plant productivity. Moreover, the results also indicate that moderate‐to‐high soil water contents during the early stages of plant development allow annual roots to overcome potentially restricting soil physical conditions.