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LIME & LIMING PRODUCTS

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 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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SOIL ACIDITY AND ITS MANAGEMENT IN CROP PRODUCTION

By | FERTILIZER PRODUCTS, LIME & LIMING PRODUCTS, PLANT & SOIL NUTRITION, Soil Acidity | 2 Comments

ARTICLE 1/2 THE NATURE OF SOIL ACIDITY AND IT’S DIAGNOSIS Acid soil conditions restricting crop growth occur widely in the eastern parts of South Africa. In the higher rainfall areas, soils are often naturally acidic; however, human intervention may accelerate acidification. It is worth noting that soil acidity problems are by no means unique to this country: worldwide, approximately 30% of the land available for cultivation is acidic. Farmers frequently have difficulty in getting to grips with the various soil acidity parameters listed in soil test reports, and furthermore, may be presented with conflicting advice regarding the use of products such as lime and gypsum. The purpose of these articles is to provide scientifically sound and practically useful answers to questions such as: “What exactly is soil acidity?”, “How does it impact crops?”, and “How is it best managed?” SOIL ACIDITY – WHAT IS IT, AND WHAT CAUSES IT? In order to gain a working understanding of soil acidity, there is a need to touch on some basic soil chemistry. Clays and organic matter in the soil carry a negative charge. In a soil that is not acidic, this negative charge is balanced by the positive charge on certain plant nutrients, in particular, calcium (Ca++) magnesium (Mg++) and potassium (K+). As soils acidify, concentrations of other non-nutrient elements, in particular hydrogen (H+) and aluminium (Al+++), as well as manganese (Mn++), increase, and they take the place of nutrients such as calcium and magnesium on the clays and organic matter (Figure 1). Under non-acidic conditions, the aluminium and manganese are contained in the clay and other soil mineral particles, but as acidity increases, clay edges start dissolving, releasing soluble aluminium and manganese into the soil. Importantly, from the perspective of managing soil acidity, it is the soluble aluminium, and sometimes manganese, which are the most important growth-limiting factors in acid soils. Furthermore, it must be borne in mind that pH measures only the concentration of hydrogen in the soil, and not that of aluminium and manganese. These considerations are of cardinal importance in terms of the development of economically sound recommendations for the correction of acidity problems. What causes soils to acidify? Although, as noted earlier, acid soils occur widely in nature, the following human activities may markedly accelerate acidification: Acid rain, resulting from atmospheric pollution by industry. This has been shown to be a major contributory factor in some Highveld areas. The use of nitrogenous fertilizers, particularly when applied in excess of immediate crop requirements. The removal of basic nutrients (calcium, magnesium and potassium) in harvested crops and animal products. Accelerated decomposition of soil organic matter as a result of tillage. SOIL ACIDITY – EFFECTS ON CROP GROWTH The effects of soil acidity on crop growth tend to be insidious, in that it is in the root zone where the major impact occurs. Damage caused to the root system and the unfavourable soil chemistry associated with excessive acidity are translated into poor crop growth, with there frequently being no classical…

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Sources of lime commonly used in South Africa

LIME SOURCES COMMONLY USED IN SOUTH AFRICA

By | LIME & LIMING PRODUCTS | No Comments

Soil acidification is a natural phenomenon which unfortunately is accelerated by numerous agricultural practices including the application of nitrogen sources containing high rates of ammonium (NH4+) nitrogen . A regular soil sampling and liming program should be central to every fertilizer program to ensure that soil productivity is not limited due to unchecked increases in soil acidity. South Africa has an abundance of good quality agricultural lime sources which are geographically well distributed and ensure that a responsible lime program is affordable. Disclaimer: The figures published are not a guarantee of analysis, they are sourced from published Product Data Sheets and provided to serve as an indicator of typical analysis which may vary due to changes in minerology of the lime sources. Please note: Consult a qualified person (Act 36 of 1947) for specific applications / recommendations.

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SOURCES OF GYPSUM IN SOUTH AFRICA

By | LIME & LIMING PRODUCTS, Soil Acidity, Sulphur | No Comments

Gypsum (CaSO4.2H2O) and its dehydrated forms are relatively common minerals that are distributed worldwide in sedimentary and evaporative deposits and produced as bye products of various industrial processes. The main sources of gypsum are from the production of phosphoric acid from rock phosphate; gypsum produced from this process is a finely grained high purity material and is commonly referred to as phosphogypsum (PG). The main sources of PG in South Africa are located in Modderfontein, Phokeng, Potchefstroom and Phalaborwa which are reported to carry in excess of 15 million tons. Other sources of gypsum are produced from flue gas desulphurization (FGD) in industrial processes in which Sulphur Dioxide (SO2) is scrubbed to meet SO2 emission standards. There are numerous deposits of natural gypsum in the Cape which are mined. Natural gypsum tends to have a larger particle size distribution than gypsum produced from industrial processes unless it is milled finely. The effect of particle size is an important factor in determining the effectiveness of gypsum amendments. Gypsum is slightly soluble in aqueous solution, dissolving to an extent of 2.5 g / l. Natural gypsum may contain traces of calcium carbonate and therefore may reflect slightly alkaline pH levels on analysis, while PG may contain free acid which may reflect as slightly acidic on analysis. Overall Gypsum has very little effect on soil pH. South African agriculture utilizes approximately 200 000 tons of gypsum per year which with an approximate 18% Sulphur (S) content provides a cost effective source of S. Disclaimer: The figures published are not a guarantee of analysis, they are sourced from published Product Data Sheets and provided to serve as an indicator of typical analysis which may vary due to industrial impurities and changes in minerology of the natural sources. Please note: Consult a qualified person (Act 36 of 1947) for specific applications / recommendations

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Save on lime costs and avoid subsoil acidity – use the right N source

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

Soil acidification is an unavoidable process that follows on from fertilization, different fertilizer products differ in their capacity to acidify the soil; substantial savings on lime costs can be made by selecting fertilizer products accordingly. Dr Erik Adriaanse explains how significant savings on lime costs may be achieved through the use of Limestone Ammonium Nitrate (LAN): Save on lime costs  

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