Acid Soil Profile Research Articles

Expected speciation of dissolved trace metals in gravitational water of acid soil profiles

Typical compositions of major and minor components of gravitational water in the various horizons of two acid soils (an acid brown earth and a humo-ferrugineous podzol), available from other studies, are used to calculate the expected dissolved speciation of selected trace metals, assuming rapid equilibrium. The weakest reported binding constants between trace metals and dissolved organic matter in soils were used in the speciation calculations using the computer program ADSORP2. In spite of the weak constants used, organic complexes are significant species of trace metals in both soil types. They are always much more abundant than inorganic complexes and in some cases (Cu and Pb in podzol A 1 horizon) they are even present in amounts similar to the free metal. The fate of the trace metals associated with the dissolved organic matter should follow the dynamics and evolution of their organic vectors. The free metal fraction whose size depends on the organic complexation constants, is available for either biological uptake (including upward recycling, a significant phenomenon in acid brown soils) or for further downward migration.

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

AbstractHighly weathered soils in the southeastern USA often have very acid, hard, infertile subsoils not readily penetrated by crop roots. An experiment on a Typic Hapludult involving deep liming, subsoil disturbance and mixing, and surface application of gypsum was conducted to investigate the possibilities of ameliorating such subsoils. Results with alfalfa (Medicago sativa L.) over 4 yr show that liming to 1 m can increase yields by 50% while merely mixing the subsoil without lime incorporation resulted in a substantial yield decline. Surface application of gypsum with sufficient time for it to penetrate the subsoil resulted in 25% yield increases. Deep liming resulted in the complete precipitation of soluble Al and increased the level of soluble Ca allowing roots to freely penetrate the subsoil. Gypsum resulted in a progressive reduction in soluble Al and an increase in soluble Ca creating a similar but lesser effect than liming. Water extraction patterns corroborated the fact that roots were penetrating chemically ameliorated subsoil. Saturation extract studies indicated that gypsum reduced the activity of Al3+ and increased that of Ca2+ substantially. These results suggest that by‐product gypsum from phosphate acid manufacture would be a feasible amendment for acid subsoils.

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

Amelioration of an Acid Soil Profile through Deep Liming and Surface Application of Gypsum

Interactions of surface drying and subsurface nutrients affecting plant growth on acidic soil profiles from an old pasture

Previous studies on soils from old pastures in southern New South Wales have demonstrated that nutrients have accumulated at the soil surface, but that the 40-100-mm depth layer in many profiles has become strongly acidic (e.g. pH 4.7), and high in extractable aluminium. Poor growth of subterranean clover has occurred on such soils during dry periods and may be associated with poor root growth in the acidic, nutrient-poor subsurface layers. Possible nutritional causes of these observations were investigated using reconstituted soil profiles. The root and shoot growth of subterranean clover, wheat, oats and lucerne were compared in unamended profiles and in profiles amended by applying nutrients or calcium carbonate (lime) to correct the more obvious deficiencies of the subsurface layers. Subterranean clover grew well as long as the surface soil remained moist, so that plants could utilise the nutrients potentially available within it. When the surface (0-40 mm) was allowed to dry but the subsurface layers remained moist, growth was poor unless phosphate was applied to the moist layer. Subsurface application of lime alone was ineffective. Nitrogen application increased clover growth in the presence of added phosphate or surface moisture, but nitrogen alone did little to alleviate the effects of surface drought. Wheat, and to a lesser extent oats, responded to subsurface lime when the surface was moist, and both responded to subsurface phosphate when the surface was dry. Lucerne responded to subsurface phosphate similarly to subterranean clover but the response was more than doubled in the presence of additional borate and lime. Lime without borate was not effective. When the surface was maintained moist, liming both the surface (0-40 mm) and subsurface layers improved the response over liming the subsurface layer only. The results suggest that declining fertility and productivity in old pastures developed on acid soils may not be rectified by liming alone, but that cultivation, ripping or drilling of phosphate, and in some cases addition of borate, may be required to improve the penetration of nutrients, particularly phosphorus, to greater depth.

Nutritional imbalances and constraints to plant growth on acid soils

Abstract The major causes of the development of strongly acid soil profiles in agricultural areas are outlined as nitrification, sulfur oxidation, and differential ion uptake by legumes, each in concert with soil‐profile leaching. The solubilities of soil minerals that determine soil‐solution levels of Al, Mn, and Mo are shown to be highly pH dependent. The chemical factors of the acid‐soil infertility factors are shown to be H toxicity, Al toxicity, Mn toxicity, Ca deficiency, and Mo deficiency. Soil pH predictor of toxic or deficient levels of soil‐solution Ions because soils vary widely in solid‐phase components that control solution ion concentrations.

Effects of subsoil calcium on the root growth of some lucerne genotypes (Medicago sativa L.) in acidic soil profiles

The root growth of lucerne was examined in an acidic soil profile modified by varying additions of calcium carbonate to different layers of the subsoil. Root growth responded strongly to changes in the concentration of exchangeable soil calcium. Symptoms of thickening, distortion and poor lateral formation occurred under low calcium treatments. The results were in agreement with the interacting effects of calcium (at 0.5–5.0mM) and aluminium ions (at 0–20,µM) on lucerne in separate solution culture experiments. Differences in root penetration were observed between three lucerne clones selected from the cultivars Hunter River and Siro Peruvian. At the first harvest, the magnitude of these differences was increased by the addition of lime to the profiles. The three genotypes produced similar total dry weight yields, but differed in their distribution of growth between shoots and roots. This distribution was not affected by the addition of lime to the subsoil. However, the length of roots in the lower layer of the profile ( > 60 cm depth) was more responsive to subsoil treatment than was total dry weight. At the final harvest, the shoot yields of two genotypes were affected by lime treatments, but that of the deepest-rooted genotype was not. The results suggest that improved genotypes could be selected from Australian lucernes for establishment in areas with acidic subsoils, but that selection on root penetration alone would not necessarily lead to increased shoot yields.

THE COVARIANCE OF PHOSPHATE SORPTION WITH OTHER SOIL PROPERTIES IN SOME BRITISH AND TROPICAL SOILS

SummaryPhosphate sorption capacity estimated by Piper's (1942) ‘anion exchange capacity’ and Bache and Williams's (1971) phosphate sorption index were correlated with soil pH, clay, organic matter, ‘free iron oxides’ and ‘extractable aluminium’ (McLean et al., 1958) for topsoil and subsoil samples from twenty tropical and twenty British acidic soil profiles. These two groups of soils did not differ significantly in phosphate sorption. Extractable aluminium and free iron oxide were well correlated with phosphate sorption, free iron oxide being superior to aluminium in freely drained British soils but not in poorly drained ones. Organic matter content correlated well with phosphate sorption for the poorly drained British soils, and for the tropical soils when sorption capacitywas measured using a high phosphate concentration.