Soil acidity is a major limitation to crop production in many parts of the world. Plant growth inhibition results from a combination of factors, including aluminum, manganese, and hydrogen ion toxicities and deficiencies of essential elements, particularly calcium, magnesium, phosphorus, and molybdenum. Agricultural management practices and acid precipitation have increased acid inputs into the ecosystem and heightened concern about soil acidity problems. While application of lime has proved to be effective in ameliorating surface soil acidity in many areas, significant soil acidity problems still exist. Scientists from Alberta, Canada, recognized the need to provide a forum for researchers from different disciplines to exchange information and ideas on solving problems of plant growth in acid soils. As a result of their efforts, the First International Symposium on Plant-Soil Interactions at Low pH was held at Grande Prairie, Alberta, Canada, in July 1987. In many acid soil areas, liming materials are not readily available, the cost may be prohibitive, or subsoil acidity cannot be corrected by surface application of lime. New management approaches involving both the plant and the soil are needed in these situations. Progress has been made in the selection and breeding of acid-tolerant plants. However, continued progress will be limited by our lack of understanding of the physiological and biochemical basis of differential acidity tolerance among plants.

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Section 1: Chemistry of acid soils.- The chemical properties of acid soils with emphasis on soils of the humid tropics.- Solubility of aluminium and silicon in acidified spodosols: Evidence for soluble aluminosilicate.- Solid phase control of aluminium activity in an artificial plant growth medium containing hydroxy-Al-montmorillonite.- Predicting toxicity of reactive "solution" aluminium using kinetic speciation.- Chemical and minerological properties and soil solution composition of acid soils from the South Pacific Islands.- Some effects of chemical weathering in three cultivated acid sulfate soils in Sweden.- Fossil acid sulfate soils in Hokkaido, Northern Japan.- Chemistry and fertility of acid andisols with special reference to subsoil acidity.- Exchangeable cations and the pH-independent distribution of cation exchange capacities in Spodosols of a forested watershed.- Salt absorption in gypsum amended acid soils.- Soil model of iron phosphate solubility.- Characteristics of soil acidity of paddy soils in relation to rice growth.- Zinc fractionation in a Cecil soil as influenced by organic acid treatments.- Geographic relationships between soil and water acidity, soil-forming factors, and acid rain.- Effect of acid rain and ozone on soil and secondary needle nutrients of loblolly pine.- Deposition of anthropogenic sulphur dioxide on soils and resulting soil acidification.- Section 2: Fertility of acid soils.- Fertility of acid soils.- Processes of soil acidification during nitrogen cycling with emphasis on legume based pastures.- Critical ammonium: nitrate uptake ratios for Douglas-fir determining rhizosphere pH and tree mortality.- Ecosystem-level significance of acid forest soil.- Plant-soil interactions associated with acid weathered soils.- Effect of phosphorus supply to the surface roots of wheat on root extension and rhizosphere chemistry in an acidic subsoil.- Effects of phosphate fertilization, lime amendments, and inoculation with VA-mycorrhizal fungi on soybeans in an acid soil.- Tolerance to acid soil conditions of the velvet beans Mucuna pruriens var. utilis and M. deeringiana. 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Root development.- Root growth of peanut cultivars and soil acidity.- Soil and soil solution property effects on root growth of aluminium tolerant and intolerant wheat cultivars.- A rapid method for predicting the lime requirement of acidic temperate soils with widely varying organic matter contents.- Effects of sample depth, and of lime and phosphorus applications on soil test levels in pasture soils.- Effects of lime additions on the availability of phosphorus and sulphur in some temperate and tropical acid soils.- Use of lime, gypsum, ana their combinations to improve nodulation and yield of groundnut in an acidic soil.- The effect of phosphate rock dissolution on soil chemical properties and wheat seedling root elongation.- Calcium magnesium imbalance in clovers: A cause of negative yield response to liming.- Soil acidity and its interactions with phosphorus availability for a range of different crop types.- Efficiency of rock phosphate as phosphatic fertilizer to rice in acid soil of Karnataka, India.- Acid soil profiles of the semiarid and subhumid tropics in Central and West Africa.- Nitrogen in soil and cotton growth as affected by liming and nitrogen fertilizer.- Liming and molybdenum effects on nitrogen uptake and grain yield of corn.- Studies on nutrition of rice cultivars under simulated acidic conditions with particular reference to iron.- Interaction of soil zinc, calcium, and pH with zinc toxicity in peanuts.- Effect of boron, lime and their residue on yield of cauliflower, leaf composition and soil properties.- Soil acidity effects on premature germination in immature maize grain.- Section 3: Management of acid soils.- The management of acid soils.- The management of soil acidity for sustainable crop production.- Characteristics of acid soils in Thailand: A Review.- Soil spatial variability and steep pasture management considerations in an acid soil environment.- Residual effects of natural bush Cajanus cajan and Tephrosia Candida on the productivity of an acid soil in southeastern Nigeria.- Old tree root channels in acid soils in the humid tropics: Important for crop root penetration, water infiltration and nitrogen management.- Effect of incorporated green manure crops on subsequent oat production in an acid, infertile silty loam.- The injection of slurries of lime, associated with deep tillage, to increase wheat production on soils with subsoil acidity.- Growth of vineyard roots into segmentally ameliorated acidic subsoils.- Long-term effects of lime in extensive pasture areas of Australia.- A field comparison of lime requirement indices for maize.- Phosphorus-lime interaction in a strongly acid upland soil grown to rice in Cavinti, Philippines.- Alfalfa yields and quality as influenced by subsurface application of phosphorus, potassium and limestone.- Establishment and growth of Vigna parkeri on an acid Florida spodosol in response to lime and phosphorus.- Effects of limestone and gypsum application to a Malaysian ultisol on soil solution composition and yields of maize and groundnut.- Use of gypsum, phosphogypsum and fluoride to ameliorate subsurface acidity in a pasture soil.- Response of upland rice and common bean to liming on an oxisol.- The effect of lime and vegetation management on non-wetting behaviour of an acid siliceous sand.- Efficiency of rock phosphate in rice-groundnut cropping system in acid soils of coastal Karnataka, India.- Influence of phosphate rock sources and rates on rice and common bean production in an oxisol.- Acidification of soil in Alberta by nitrogen fertilizers applied to bromegrass.- Acidification of forest soil by elemental sulphur dust.- Section 4: Microbial relations in acid soils.- Soil acidity and the microbial population: Survival and growth of bacteria in low pH.- Response of Rhizobium leguminosarum bv. phaseoli to acidity.- Increased yield in annual species of Medicago grown in acidic soil in response to inoculation with acid tolerant Rhizobium meliloti.- Rhizobium meliloti inoculation of alfalfa selected for tolerance to acid aluminium-rich soils.- Effects of pH and Al3+ activity on survival of Rhizobium leguminosarum bv. trifolii in a simple solution and on nodulation of red clover in acid soils.- Tolerance of winged bean (Psophocarpus tetragonolohus) and its symbiotic system to soil acidity.- Effects of soil acidity f…