Monthly Archives

June 2018

FACTORS DETERMINING THE EFFICACY OF AGRICULTURAL LIME

By | LIME & LIMING PRODUCTS | One Comment

South Africa has an abundance of agricultural lime sources distributed throughout the country which should enable farmers to source lime as economically as possible. Lime is classified as a Group 2 fertilizer and regulated by The Fertilizer, Farm Feeds and Agricultural Remedies Act of 1947 (Act 36 of 1947). Dolomitic and calcitic lime sources are used to ameliorate soil acidity, Al3+ and Mn2+ toxicities, raise soil pH and manage calcium and magnesium levels in the soil. The sources of lime may be of both natural and industrial origin and vary significantly in their chemical and physical properties which in turn will determine the efficacy the product being used. Factors affecting efficacy of lime In the article, Soil Acidity and its Management in Crop and Pasture Production; Miles and Farina indicate that the effectiveness of various liming materials varies widely, with the following factors being of particular importance: Chemical purity ─ the presence or otherwise of non-reactive materials such as sand and clay greatly affects the neutralizing value of the lime (importantly, the colour of the liming material is not a reliable indicator of its quality!). Chemical composition ─ the nature of the calcium and magnesium compounds present. Fineness ─ the finer the lime particles, the faster will be their reaction in the soil. Lime particles larger than 0.84 mm in diameter (about the size of a match head) are of little value. Very coarse liming materials are completely ineffective. Hardness ─ the solubility, and hence neutralizing value, of lime depends on whether it is derived from hard crystalline material or from softer relatively unconsolidated material. Where uncertainty exists as to the quality of a particular liming material, they advise that a sample should be submitted for analysis. The rate of chemical reaction When lime is applied to the soil it reacts with the acidic components of the soil, H+, Al3+ and Mn2+ , the rate of chemical reaction is determined by temperature, surface area for reaction, relative concentration of the reactants and the presence of soil moisture. Four factors determine the efficiency of lime: Rate of application Purity (CCE) Particle size distribution Degree of incorporation into soil Chemical purity – Calcium Carbonate Equivalent (CCE) The chemical composition of lime varies according to its geological or industrial origin. The term calcium carbonate equivalent (CCE) is a measure used to distinguish the neutralizing capacity of a lime source relative to the mass of pure calcium carbonate required to neutralize hydrochloric acid (HCl). The CCE of pure calcium carbonate is rated as 100%, pure magnesium carbonate has a lower molecular mass and as such less magnesium carbonate is required to neutralize the equivalent amount of HCl, the CCE of magnesium carbonate is 119%. The CCE of lime will vary according to the calcium (Ca) and magnesium (Mg) content as well as other impurities such as sand and clay; large variances in CCE may exist between different sources of lime. The minimum CCE of lime in terms of Act 36 is 70%. Fineness –…

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Soil Fertility and Plant Nutrition Symposium

By | Conferences and Training | No Comments

Book your place for the FERTASA  Soil Fertility and Plant Nutrition Symposium to held on 21 August 2018 at the CSIR International Convention Centre, Pretoria. The symposium theme is “Effective Stewardship of Fertilizer in Practice”. Guest speakers include Prof Patrick Brown from the University of California, covering Foliar Fertilization; Prof Patrick du Jardin from Gembloux Agri-Bio Tech – Univesity of Liege covering Bio Stimulants to Enhance Nutrient use Efficiency in Crop Plants; Prof Joanna Dames from Rhodes University covering  Mycorrhiza – Born to be friends; Dr George Ebert covering Controlled Efficiency; Dr Johan Habig covering Soil Health Quantification; Dr Bridgitta Steyn covering Stewardship of the microbial ecosystem of agricultural soil and Dr Arrie van Vuuren covering Effective Placement of Fertilizer. Register by 29 June to take advantage of the Early Bird Registration Fee. Final Programme – 2018 Symposium INDIVIDUAL Registration Form 2018 GROUP Registration Form 2018

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SOIL ACIDITY AND ITS MANAGEMENT IN CROP AND PASTURE PRODUCTION

By | LIME & LIMING PRODUCTS, PLANT & SOIL NUTRITION, Soil Acidity | No Comments

To read article 1/2 click: http://agrispex.co.za/soil-acidity-and-its-management-in-crop-production/ ARTICLE 2/2 THE USE OF LIME AND GYPSUM IN MANAGING SOIL ACIDITY In the first article in this series, we discussed the nature of soil acidity. Particular attention was drawn to the harmful effects of soluble aluminium on root growth and function, and how crop species differ in their ability to tolerate aluminium toxicity. In this second article, we focus on practical aspects of soil acidity management. LIME AND GYPSUM — HOW DO THEY DIFFER? Lime and gypsum are chemically very different products, and consequently their effects on the soil are quite dissimilar. In the agricultural context, ‘lime’ refers to any product in which the calcium and magnesium compounds are able to neutralize soil acidity. Carbonates of calcium and magnesium are the most widely used for this purpose. Dolomitic lime contains a minimum of 15% magnesium carbonate, while calcitic limes have less magnesium carbonate than this. In addition to natural carbonates, various by-products of industrial processes are frequently used as liming materials; these include calcium oxide (burnt lime), calcium hydroxide (slaked lime) and calcium silicate (slag). Gypsum, on the other hand, is calcium sulphate, a neutral salt. It is a valuable calcium and sulphur fertilizer and is much more soluble than lime. In addition, it leaches readily into the subsoil and, in highly weathered (naturally acidic) soils, the sulphate component displaces OH- ions from the clay surfaces. These, in turn, convert soluble aluminium to unavailable aluminium hydroxide. The effectiveness of various liming materials varies widely, with the following factors being particularly important in this regard: Chemical purity ─ the presence or otherwise of non-reactive materials such as sand and clay greatly affects the neutralizing value of the lime (importantly, the colour of the liming material is not a reliable indicator of its quality!). Chemical composition ─ the nature of the calcium and magnesium compounds present. Fineness ─ the finer the lime particles, the faster will be their reaction in the soil. Lime particles larger than 0.84 mm in diameter (about the size of a match head) are of little value. Very coarse liming materials are completely ineffective. Hardness ─ the solubility, and hence neutralizing value, of lime depends on whether it is derived from hard crystalline material or from softer relatively unconsolidated material. Where uncertainty exists as to the quality of a particular liming material, a sample should be submitted for analysis. ACTION OF LIME AND GYPSUM IN SOILS The major effects of lime on soil properties are: an increase in soil pH; a decrease in soluble aluminium and acid saturation levels; an increase in calcium and magnesium levels. The value of dolomitic lime as a magnesium fertilizer is often overlooked. Although several magnesium fertilizers are commercially available, they tend to be prohibitively expensive, and dolomitic lime remains the most cost-effective way of increasing soil magnesium levels. The neutralizing effect of lime on soil aluminium and hydrogen is illustrated in Figure 1. Importantly, the soil must be moist for lime to react. The solid aluminium…

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