Effect of root systems on preferential flow in swelling soil

Abstract

Permeability problems on irrigated soils may be alleviated by root systems that increase water flow by creating macropores. Infiltration rates have been shown to increase where plant roots decay and serve as preferential flow paths. For low-organic-matter swelling soil, there is a question whether macropores are able to resist the lateral swelling forces of the soil. The objective of this study was to observe preferential water flow paths in a swelling soil under two cropping systems. A Holtville silty clay (clayey-over-loamy, montmorillonitic Typic Torrifluvent) was observed in situ. Two crops, alfalfa (Medicago saliva, L.) and wheat (Triticum turgidum, L.) provided sharply contrasting root systems, with wheat possessing fine, fibrous roots; alfalfa on the other hand, has a taproot system. Macropores were observed after applying soil-adsorbing methylene blue dye to irrigation water.Shrinkage cracks failed to conduct dye after 10 minutes into a flood irrigation.Earthworm (Lubricus terrestris) channels were also not stable. However, decaying roots of alfalfa produced stable macropores, while wheat produced no such macropores. The influence of alfalfa-root-induced macropores was demonstrated by 's (1989, 1990) findings on sandy loam soils.

Effects of fine root length density and root biomass on soil preferential flow in forest ecosystems

“…Our results indicate that fine root length density decrease with increasing distance from soil surface which supports early and recent studies (Mitchell et al, 1995;Tracy et al, 2013). Those results collected from fine root length density imply that plant roots content are higher in preferential pathways than in soil matrix, supporting studies like Bundt et al (2000Bundt et al ( , 2001, and the results are also in agreement with Bonger et al (2010) and Bengough (2012), because plant fine roots usually form root channels called pref- 10 ties (e.g., soil bulk density, porosity, organic carbon, citation exchange capacity and so on).…”

“…More decaying or decayed plant roots as well as fine plant roots are distributed on the soil surface. Compared with living plant roots, decayed roots were more effective to create preferential pathways (Mitchell et al, 1995). Furthermore, plant roots could release complex organic compounds (e.g., amino acids and organic acids) into the soils to prompt plant growth (Bengough, 2012).…”

Significance of tree roots for preferential infiltration in stagnic soils

“…These findings indicate that it is impossible to specify all preferential flow paths by means of root measurements. It has been shown that cracks adjacent to living alfalfa roots have only a temporary effect, while decaying roots produce stable macropores (Mitchell et al, 1995). Noguchi et al (1997) pointed out that at least 70% of the macropores (≥2 mm) in the topsoil and 55% in the subsoil in a forest soil in Japan were associated with roots.…”

Root-enhanced Infiltration in Stormwater Bioretention Facilities in Portland, Oregon

“…Within silty clay fields of alfalfa (Medicago saliva) in California, Mitchel et al (1995) attributed an infiltration increase from 0.13 cm/hr in May to 0.32 cm/hr in October to macropores created from decaying tap roots. Rasse et al (2000) showed alfalfa root systems increased soil porosity and infiltration rates in alfalfa treatments compared to bare soil treatments in July using a mini-rhizotron in western Michigan.…”