Fragipan horizon fragmentation in slaking experiments with amendment materials and ryegrass root tissue extracts.

A D Karathanasis,L W Murdock,J Grove,C J Matocha,Y L Thompson

doi:10.1155/2014/276892

Abstract

Slaking experiments were conducted of fragipan clods immersed in solutions of poultry manure, aerobically digested biosolid waste (ADB), fluidized bed combustion byproduct (FBC), D-H2O, CaCO3, NaF, Na-hexa-metaphosphate, and ryegrass root biomass. The fragipan clods were sampled from the Btx horizon of an Oxyaquic Fragiudalf in Kentucky. Wet sieving aggregate analysis showed significantly better fragmentation in the NaF, Na-hexa-metaphosphate, and ryegrass root solutions with a mean weight diameter range of 15.5–18.8 mm compared to the 44.2–47.9 mm of the poultry manure, ADB, and FBC treatments. Dissolved Si, Al, Fe, and Mn levels released in solution were ambiguous. The poor efficiency of the poultry manure, ADB, and FBC treatments was attributed to their high ionic strength, while the high efficiency of the NaF, Na-hexa-metaphosphate, and rye grass root solutions to their high sodium soluble ratio (SSR). A slaking mechanism is proposed suggesting that aqueous solutions with high SSR penetrate faster into the fragipan capillaries and generate the critical swelling pressure and shearing stress required to rupture the fragipan into several fragments. Additional fragmentation occurs in a followup stage during which potential Si, Al, Fe, and Mn binding agents may be released into solution. Field experiments testing these findings are in progress.

Highlights

Fragipans are naturally causing restrictive layers occurring in about 53,000 km2 of Kentucky soils and more than 970,000 km2 in the US [1, 2]
The fragipan samples were treated with solutions/extracts from the following materials: deionized water (D-H2O), reagent grade CaCO3 at solubility strength, 0.005 M NaF, 0.005 M Na-hexa-meta-phosphate, an aerobically digested biosolid waste (ADB) collected from a waste water treatment plant in Jessamine County, KY, a fluidized bed combustion byproduct (FBC) from a coal power facility, broiler litter collected from a poultry facility, and ryegrass root biomass collected from a field where it was grown as a cover crop
Since minimal or no fragmentation occurs in these treatments, most of the Si, Al, Fe, or Mn released during the experiments was dissolved from the periphery of the fragipan clods and not from the interior of the fragments. This release may be enhanced by dissolved organic carbon (DOC) in solutions of organic amendments but organic coatings of fragipan surfaces may inhibit water penetration in the capillaries by creating a semihydrophobic barrier. The findings of these experiments suggested that amendment materials producing solutions with relatively low ionic strength and elevated sodium soluble ratio (SSR) (NaF, Na-hexa-meta-phosphate, and ryegrass root) create an environment more conducive to fragipan slaking than that of high electrolyte concentrations, Ca, Mg, or DOC enriched solutions

Summary

Introduction

Fragipans are naturally causing restrictive layers occurring in about 53,000 km of Kentucky soils and more than 970,000 km in the US [1, 2] They usually form as a result of weathering of primary minerals (mainly feldspars) in relatively acidic environments. The fragipan, which usually occurs at depths between 45 and 60 cm from the soil surface, greatly restricts water movement and root growth [6]. It reduces the water holding potential in these soils to about one-half of that of many other crop producing soils [7]. By far the biggest production problem for corn and soybeans grown on these soils is limited water holding capacity, which may reduce yields by at least 20–25% [10, 11]

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