Use of marble sludge and biochar to improve soil water retention capacity

Agriculture and mining are the most important economic activities in the province of Almería (SE Spain) and generate large amounts of waste. Almería is one of the driest regions in Europe, and its water resources come mainly from groundwater. The high water consumption of greenhouses (between 5000 and 6000 m3 ha-1 y-1) has resulted in a sharp decline of water table levels and a worsening of water quality. Therefore, it is necessary to implement actions that lead to the more efficient use of irrigation water. The objective of this study was to evaluate the effect of two waste types (marble sludge and biochar from greenhouse plant debris) on the soil water holding capacity. Three treatments were performed in pots using two of the most common soils in greenhouses. A lettuce seedling was planted in each pot, and the volumetric water content was periodically controlled. The first treatment contained 600 g of soil, the second treatment contained 200 g of marble sludge at the bottom and 400 g of soil on the surface, and the third treatment contained 150 g of marble sludge at the bottom, 50 g of biochar in the middle and 400 g of soil on the surface. The results showed that the use of marble sludge, biochar and the combination of both waste types increased water holding capacity. The volumetric water content was relatively high for a longer time, allowing for a reduction in watering frequency and enabling more efficient water use. The waste applications were most effective in the soil with a thicker texture and lower evaporation rate.