Hydroxyaluminosilicate (HAS) ions were prepared from solutions containing hydroxyaluminum (HyA) ions and orthosilicic acids at an Al concentration of ≈4 mM; Si/Al molar ratios of 0, 0.25, 0.5, and 1.0; and NaOH/Al molar ratios of 1.0, 2.0, and 2.5. Phosphate retention behavior of montmorillonite (Mt) carrying nonexchangeably adsorbed HyA, HAS ions, or both (HyA/HAS‐Mt complexes) was studied at equilibrating solution pH of ≈5.0. The HyA/HAS‐Mt complexes showed larger phosphate retention capacities than untreated Mt. Retention of phosphate by these complexes at 0.5 to 50 mM initial P concentrations decreased with increasing NaOH/Al and Si/Al ratios of the hydroxy materials adsorbed on Mt. Phosphate, probably retained initially through surface complexation and ligand exchange reactions principally with OH or OH2 groups, coordinated with Al atoms at the broken edges of HyA or HAS polymers adsorbed on the external planar surfaces and in the interlayer spaces of Mt. This was followed by expulsion of the phosphated hydroxy materials from the Mt interlayers to the ambient solution, and finally, precipitation as amorphous Al‐phosphate solid phases. Results of this study thus merit attention in P‐fertility management as well as indicate a probable P‐induced weathering process in acidic nonallophanic Andisols and in Red‐Yellow soils (Hapludalfs and Hapludults) with a predominance of hydroxy‐interlayered minerals.
Soil water repellency (SWR) is a phenomenon that can reduce water infiltration into the soil. Generally, the quantity and quality of soil organic matter and the soil moisture content will govern the severity of SWR. The objectives of this study were (i) to characterize SWR for greenhouse and grassland soils using the water drop penetration time (WDPT) test and (ii) to find relationships among the field and laboratory WDPT (WDPTfield and WDPTlab), and the SDM measurements. Two farms that produce vegetables in greenhouses from Japan (Mizuho farm, Miki city, Hyogo) and a beef farm from New Zealand (Tihoi, near Taupo, Waikato) under perennial mixed grass (Lolium perenne L. and Trifolium repens L.) were selected as experimental sites. The New Zealand hillslope site was located on an Andosol. In the greenhouses at the two Japanese sites, vegetables such as spinach (Spinacia oleracea) and spring onion (Allium spp.) were grown on fine-textured Haplic Brown Lowland Soil. The latter soils were fertilized once a season with farm-made compost. Water repellency was measured along a rectangular grid and selected transects. The WDPT was measured using micro-syringe water droplets (50 µL) with five replicates. The WDPTlab and SDM were measured using repacked soil cores. The values of WDPTfield varied widely from non-repellent to extreme SWR. The water repellent soil has observed for grassland soils at pF (= log [−ψ], where ψ is the soil water matric potential in centimeters of H2O) of 3.2 -4.4 range. The measured WDPTlab showed a linear relationship with the measured SDM (r 2 = 0.80).
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