March 2011 for web.indd - OVK

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Safex-prys bied goeie ge leent heid vir die ver skansing van die gewasse. Pro du sente kan ge rus hul naaste graan kantoor in Lady brand en Hopetown skakel om die jong ste strategieë te benut vir optimale bemarking van hul graan. THE RECLAMATION OF SALINE AND ALKALI SOILS ARTICLE: Dirk Gunter Alkali soils have a very low water infiltration rate when it is wet and both alkali and saline-alkali soils tend to form a surface crust (soil capping) when it is dry. This trait makes it difficult for irrigation water to infiltrate and it tends to run off. By adding gypsum to irrigation water, the hydraulic conductivity is increased. This increases the infiltration rate of the irrigation water. To know which saline and alkali soils can be reclaimed using gypsum, one must remember that saline and alkali soils can be separated into three groups, namely: Saline soils: These soils have a high salt content and water infiltration and can be reclaimed by leaching of the soluble salts. Alkali soils: These soils have a high percentage of ex - change able sodium, a low soluble salt content, a pH higher than 8,5 and a low water infiltration rate. They 18 can be reclaimed by the application of gypsum and subsequent leaching of the sodium salts. Saline-alkali soils: These soils are a combination of the first two i.e. they have high levels of soluble salts, a high percentage of exchangeable sodium, a pH lower than 8,5 and a low water infiltration rate. They can be reclaimed by the addition of gypsum and subsequent leaching of the sodium and soluble salts. Saline-alkali soils are detrimental to plant growth be cause of the presence of high salt concentrations that induce high osmotic pressures, the high pH, toxicity of anions such as borates and bicarbonates and the detrimental effect of sodium on plant nutrition and the physical con dition of the soil. Crop production on saline alkali soils are problematic and needs extremely good manage ment practices. Saline alkali soils can be reclaimed by leaching of the soluble salts and by replacing the sodium caption on the clay colloids by calcium. Drainage of the soil is a prerequisite followed by a predetermined planned overirrigation programme. Saline soils need only to be drained to be able to leach the excess soluble salts present. In the case of alkali or Contents saline-alkali soils the exchangeable sodium percentage • must be reduced to less than 15 % through the addition of gypsum, followed by leaching of the replaced sodium and other salts. Inhoud
The amount of gypsum to replace the sodium on the clay particles are between 3,6 and 4,2 tons for each 1 cmol exchangeable sodium per hectare per 25 cm soil depth. The gypsum must be broadcasted and ploughed in. The better the mixing and the deeper it is incorporated the better and quicker the reaction will be. This must be followed by a planned leaching programme. An irrigation of 1 000 mm of water is capable of solubilising 10 to 13 tonnes of gypsum per hectare. Acidifying pro ducts to reclaim saline-alkali and alkali soils can only be used if enough insoluble calcium salts are present in the soil or it can be applied with gypsum. Advantages of gypsum: • It improves soil structure. • Prevents soil capping. • Lowers aluminium in acid soils. • Supplies calcium and sulphur as nutrients. When applying these practices accurate calculations are necessary and a technical advisor should be consulted. Vroue: ASTER SÊ VERSE JUBEL OOR DIE LANDBOU En so sleep Oubaas my toe saam na ’n boere-funksie waar Mohammed Karaan die spreker was. Prof. Karaan – die groot, donker laventel boer en landbou-akademikus 19 van Stellenbosch wat Afrikaans liefhet en koester. Hy praat die taal met soveel oorgawe, emosie en genade dat dit ’n mens ver stom laat. Hy waarsku in Afrikaans, hy moedig aan en hy raps mense oor die vingers in die taal van sy hart. Op die mooie môre in die Oos-Vry staat haal hy aan uit Vroegherfs van NP van Wyk Louw om ons te waarsku teen die gevare van oor dadigheid, van finansiële onverant woordelikheid: “O Heer, laat hierdie dae heilig word: Laat alles val wat pronk en sieraad was.” Ons kan nie meer uitspattigheid be kos tig soos om sushi van naakte lywe af te eet nie, sê hy. Die wêreld is besig om ’n armer plek te word en kos al hoe skaarser. Nie omdat daar te min is nie, maar omdat dit te duur gaan word. Daarom is dit tyd dat ons alles laat val wat “pronk” en “sieraad” is. Ek dink onwillekeurig aan die Suid- Afrikaanse Jeugkommissie wat R100 miljoen op ’n mislukte internasionale jeug-kongres gemors het. “O Here, wees ons genadig,” kramp my hart. Ek is seker Karaan s’n ook. Toe verander hy van rat en lees Lina Spies se Paternoster vir Suid-Afrika vir ons. “Here, laat die name geheilig word Contents • van al die kinders van die land – van hulle wat modderkoekies gebak het uit sy aarde, dassies skrikgemaak het in sy klowe, wol getrap het in sy krale.” Inhoud
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March 2011 for web.indd - OVK

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