To read the original article referring to these photos click: http://agrispex.co.za/soil-acidity-and-its-management-in-crop-production/ GALLERY CONTENT: Maize(5), Rye Grass (1), Soya Bean(1), Sugar Cane(1)
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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…
Dr Mart Farina started his career as a Land Development Officer in Rhodesia and then worked as a soil fertility researcher in the South African Department of Agriculture and the Agricultural Research Council from 1965 to 1998. Since then, he has consulted to Omnia Fertilizer, the FAO in Ethiopia, Nordic Fertilizers in Central America, and to government agencies and individual farmers in Kenya, Tanzania, the DRC, Zambia, Madagascar, Malawi, Zimbabwe and the Republic of Guinea. During the course of his career Mart has authored or co-authored 66 refereed scientific papers, 23 of which were published in international journals. In the interests of technology transfer to the agricultural industry Mart has also published over 50 semi-scientific and popular articles and addressed some 300 farmer’s days; he has also presented over 70 papers at scientific conferences and technical symposia. Mart was a Research Fellow at the University of Georgia, U.S.A., during 1978 and has participated in 10 international conferences on soil fertility, on five occasions as an invited speaker. Mart has been the recipient of numerous awards including six from the Fertilizer Society of South Africa (FERTASA), the BP Scholarship in Agriculture, the Gold Medal for Research from the South African Society of Crop Production, and the Sanachem Prize. In 1988 and 2005 was the Natal Agricultural Writer’s Association Agriculturist of the Year, in 1984 the National Maize Producer’s Maize Researcher of the Year, and in 1994 the Summer Grain Centre’s Researcher of the Year. Mart served as the standing member for Africa, on the International Steering Committee for Symposia on Plant-Soil Interactions at Low pH from 1993 until 2001. Mart has Honorary Membership of the South African Society of Crop Production and is a 40-year Emeritus Member of the Agronomy Society of America and the Soil Science Society of America. Contact details: farina@netfocus.co.za
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Dr Neil Miles consulting soil scientist
Neil Miles is a consulting soil scientist based in Mount Edgecombe. Prior to entering into consultancy, he spent 28 years with the KZN Department of Agriculture, as a research scientist and research manager, followed by 10 years in research and advisory work with the South African Sugarcane Research Institute (SASRI).
Neil played a leading role in the development of both the Cedara Fertilizer Advisory Service and SASRI’s Fertiliser Advisory Service (FAS). His PhD, through the University of Natal, focused on the nutrition of intensive pastures. Neil’s particular interests are soil health and the nutrition of crops and pastures.
Contact Neil: milesofsoil@gmail.com