The use of high molecular weight flocculants in agriculture

Soil crumbs owe their stability in part to the presence of naturally occurring polymeric materials (humus), which bind to the soil. The first synthetic polymers to improve soil structure and enhance crop growth were introduced in 1951. The results of incorporating polymers into soil were spectacular, but the dose rates required made their use uneconomical. 

The polymers are effective through two mechanisms, soil binding and flocculation. The polymer can bind to soil crumbs, giving structural stability. This reduces crumb breakdown on irrigation and maintains an open structure, which facilitates infiltration. This mechanism 

Studies have shown that high molecular weight anionic polyacrylamide polymers are most effective as soil stabUisers [76]. These polymers bind primarily to calcium ions that are in themselves bound to anionic sites on the surface of the soil crumb (a process known as calcium bridging or salt linkage). The anionic nature of the soil crumb arises due to the anionic surface charge of the clay portion within the sod. 

More recently polymers have been incorporated directly into liquid and solid based fertilisers, thus giving farmers a greater choice of application technique for the soil stabihser. 

Optimum product choice is required to ensure the most efficient use of the flocculants and coagulants is made. This is accomplished through choice of chemical type, that ensures adsorption onto particle siufaces, and via modifying molecular weight and structure that is largely dependent on the separation techniques employed. 

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