Studies of Clay Skins in a Cecil (Typic Hapludult) Soil: II. Effect on Plant Growth and Nutrient Uptake

Abstract

A greenhouse experiment was conducted to study the effect clay skins may have on plant growth and N, P, and K uptake. Wheat (Triticum vulgare, var. Wakeland) plants were grown in uncoated aggregates and in large and small clay skin‐coated peds from the B22t horizon of a Cecil (Typic Hapludult) soil for 4 weeks. Data obtained for dry weight and total N, P, and K content of the plants were statistically analyzed. Plants grown in the uncoated aggregates had higher dry weights and more total N, P, and K than those grown in either the large or small coated peds. Most of the plant roots grew outside of the coated peds with a concentration of fine roots on the surface of the clay skin. It is hypothesized that the clay skins reduced plant growth and nutrient uptake (especially P and K) either by serving as a barrier for root growth and/or by slowing ion diffusion from the soil peds into the inter‐ped soil solution.

Submicroscopic measurements of tracer distribution related to surface features of soil aggregates

“…Plants grown in soil with uncoated peds had the highest content of N, P and K. It was believed that clay films affected the growth of roots by acting as membranes, which restricted root growth. It was also concluded that the continuity of clay films, with their high clay content and continuous fabric orientation, may have decreased or restricted the diffusion of exchanging ions (namely K and PO 4 ) into and out of the aggregate interiors (Khalifa and Buol, 1969). These findings are consistent with those of Lai and Mortland (1968), who found that the coefficient for Na diffusion flux perpendicular to the clay platelets was only 15 to 20% of the diffusion coefficient for flux parallel to clay platelets.…”

“…Adsorption and retention of a chemical during such flow events could be affected by the presence of clay films, reoriented clay layers, and organic-rich linings coating the flow paths (Gerber et al, 1973, Khalifa and Buol, 1969, Miller et al, 1971, Soileau et al, 1964, Turner and Steele, 1988.…”

“…Soileau et al (1964) found that plant growth and potassium uptake were restricted in the presence of iron-kaolinite coatings on K-rich illite aggregates compared with plants grown in soil that had aggregates without coatings. In the study by Khalifa and Buol (1969), plants were grown in soil with uncoated aggregates and in soil with small and large clay filmcoated peds. Most of the plant roots were growing outside coated peds, with concentration of roots located on clay film surfaces.…”

Long‐term Changes in Soil Macro‐ and Micromorphological Properties Under the Influence of Peat Debris

“…The thickest and most lustrous skins are found in the diagonal or transverse channels where the rate of downward movement is slowest. Root hairs are confined to and proliferate on these surfaces, either because the coatings (1) act as a barrier to root penetration, (2) have higher levels of available nutrients as is the case for clay skins (Khalifa and Buol, 1969;Soileau et al 1965), or (3) stimulate root initiation (Schnitzer and Poapst, 1967).…”

Advancing the frontiers of soil science towards a geoscience

“…While coatings may comprise a small proportion of the total ped volume, they have inordinate impact on biophysical soil attributes, flow pathways, chemical dynamics at the ped/macrovoid interfaces. Examples would include biotic activity (root and other biopore distribution patterns), sorption/desorption kinetics, diffusion rates, mass flow, gas transport, and biomass productivity (e.g., Miller et al, 1971;Soileau et al, 1964;Khalifa and Buol, 1969;Gerber et al, 1974;Sexstone et al, 1985;Asady and Smucker, 1989).…”