Clay has been added to sandy soils at ‘De Marke’ experimental dairy farm with the aim of improving the sandy soil. The clay soil used was released during developments. A three-year trial was conducted with maize and grass, focusing on soil moisture content and crop yields. It has also been established for the maize field it followed that the moisture-holding capacity increased by the addition of clay, and significantly higher yields were measured than in the untreated test plots. For the grassland it was found that more moisture is retained in the soil with clay, but significantly different grass yields were not registered.