The researchers aimed to understand how much water soil can hold and how much is available for plants in subtropical Brazilian soils. They collected data on soil properties and water retention, then created formulas to estimate plant available water. The formulas worked best for soils in the same region and were less accurate for soils from other areas. They found that soil texture affects how much water can be held, with silt and sand content playing a bigger role than clay. Soils with more silt and less weathering had higher water retention and plant available water capacity.