Explanation Text (EXAMPLE)

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The Effects Of Acid Soil

(General Statement)Soils with a pH of less than 7.0 are acid. The lower the pH, the more acid the soil. When soil pH falls below 5.5, plant growth is affected. Crop yields decrease, reducing productivity.

(Explanation)Soils provide water and nutrients for plant growth and development. Essential plant nutrients include phosphorus, nitrogen, potassium and sulfur. Plants require other elements such as molybdenum, in smaller quantities. Some elements e.g. aluminum and manganese, are toxic to plants.

Nutrients become available to plants when they are dissolved in water. Plants are able to take up phosphate, nitrate, and potassium and sulfate ions in solution.

The solubility of nutrients changes with pH. In acid soils (low pH), molybdenum becomes less soluble and aluminum becomes more soluble. Therefore, plant growth may be affected by either a deficiency of molybdenum or too much aluminum.

Both crop and pasture plants are affected by acid soils. there may be a range of symptoms. Crops and pastures may be poorly established resulting in patchy and uneven growth. Plant leaves may go yellow and die at the tips. The root system of the plant may be stunted. Crops may yield less.

Plants vary in their sensitivity to low pH. Canola and Lucerne are very sensitive to acid soils so do not grow well. Lupines and triticale are tolerant to soils of low pH so they still perform well.

(Closing)Land can become unproductive if acid soil is left untreated. Incorporating lime into the soil raises the pH. Therefore, liming soil can reverse the effects of acid soil on plants and return a paddock to productivity.