Effect of soil-ph and organic-matter on labile aluminium in soils under permanent grass

The rates of extraction of Na, K, Mg, Ca, and Al with 1M NH4 NO3 from the mineral-and organic-rich layers of some Park Grass (Rothamsted) soils were measured at the pH of the soil. Below pH 3.7 exchangeable Al, derived from the kinetics curve, increases with decreasing soil pH and is less in the organic-rich layer. The sum of the basic exchangeable cations, ¿(Na + K + Mg + Ca), increases with increasing soil pH and is more in the organic-rich layer. The extraction of exchangeable Al obeys first order kinetics, the rate constant being similar for all the soils (mean value 36 ± 7 × 10¿6|s¿1), which implies that exchangeable Al is released from surfaces with similar properties for the adsorption of Al, and that the rate is not affected by soil pH and organic matter. The rate of extraction of non-exchangeable Al is the same in the mineral-and organic-rich layers of each soil, and is maximal at about pH 3.7, decreasing sharply at more and less acid pH values.Peer Reviewe

Alteration in the Surface Properties of Soils by Ion Exchange Resins

RESP-463

Using radiotracers in soil chemistry research

RESP-658

Charge heterogeneity in smectites

The heterogeneity of sites for Ca>K exchange was examined by microcalorimetry in the <0.2-/zm fractions of some selected smectites. Six groups of sites, ranging in exothermic exchange enthalpy (-d(AHx)/dx) from 5.7 to 10.9 kJ/eq were identified. In Wyoming bentonites, only three groups with enthalpies of 5.7 to 7.5 kJ/eq were distinguished, although in the 0.2-1.0-p~m fraction, a 10.7-kJ/eq group was also observed. Redhill and Camp Berteau smectites contained, in addition, groups with enthalpies of 8.7-10.9 kJ/eq, but a New Mexico sample only had groups with the higher values. Thus, the exchange enthalpies of four main groups of sites (reclassified from those observed) appear to be inversely related to the extents of interlayer expansion in the samples by the adsorption of polar molecules. Consequently, a 'true montmorillonite,' such as a <0.2-/~m Wyoming bentonite, contains only fully expanding layers with -d(AHx)/dx values between 5.7 and 7.5 kJ/eq. As such, it is less heterogeneous and should have a much greater swelling capability than Camp Berteau montmorillonite which has, in addition, groups with exchange enthalpies of 8.7 and 10.3 kJ/eq

Potassium reserves in British soils. I. The Rothamsted Classical Experiments

RESP-581

Potassium reserves in British soils: II. Soils from different parent materials

RESP-

Thermodynamics of K-Ca exchange in soils .1. Effects of potassium and organic-matter residues in soils from the Broadbalk and Saxmundham Rotation I Experiments

The standard and differential thermodynamic properties of K‐Ca exchange in soils from the Broadbalk (Batcombe series) and Saxmundham Rotation I (Beccles series) Experiments were evaluated for selected manurial treatments, using exchange isotherms and calorimetric measurements. The Beccles soil had a greater preference for K than the Batcombe soil in all the comparable treatments (Nil, PK and FYM). In all the soils, enthalpic forces favoured K preference but entropic forces Ca preference; in all but two cases the magnitude of the enthalpic forces were greater, resulting in K preference (positive ‐ΔGo). The ‐ΔHo values of the soils did not vary greatly, and the main cause of variation in ‐ΔGo values was that in ‐TΔSo values. Residual fertilizer K and FYM residues decreased preference for K at both locations, but more so at Broadbalk than at Saxmundham, presumably because of the greater duration and amount of K manuring at Broadbalk. FYM residues had a very complex effect on the exchange characteristics of Broadbalk soil. It is suggested that these differences are caused by the different pH values of the surface soils before they came into arable usage, which reflect their contrasting parent materials and pedogenic histories, and by the different durations and extents of manuring in the two experiments

Isotopic Exchange of Phosphates in Soil

RESP-449

An automatic micro-injection system and its use in the microcalorimetry of cation-exchange sorption

Details are given of a remote-control device which can deliver known microlite volumes of solutions simultaneously to the 'control' and 'reaction' cells in the LKB calorimeter, and can do so accurately, automatically and at preset intervals. The device incorporates Hamilton microsyringes. The facility for injection at preset intervals is designed to allow the heat change after each addition of reacting solution to be recorded completely before the next addition, the interval for a reaction being predetermined in a pilot scale experiment. A method is described for measuring different enthalpies of potassium-calcium exchange in soils and clays using an LKB microcalorimeter incorporating this device. This achieves a considerable economy in time over the method of deriving information from the thermodynamic treatments of cation-exchange isotherms. The degree of cation-saturation is interpolated from a parallel 'isotherm' experiment on a macroscale in which several consecutive additions in the 'calorimeter' experiment are telescoped into single steps