soil amelioration, a viticultural practice for improving soils by the addition of so-called soil amendments. These can include fertilizers to overcome mineral nutrient deficiencies (such as superphosphate to add phosphorus); lime, which will overcome soil acidity; gypsum and organic matter, which will improve soil structure. These ameliorants are spread on the soil surface, and occasionally turned in by cultivation. Where there is a need for deep placement, as in liming or the application of rock phosphate (see fertilizers), then ripping implements drawn by powerful bulldozers are used before planting. When the lime and gypsum are finely ground, special applicators allow these normally insoluble products to be added through drip irrigation systems but the drippers are easily blocked.