Water and nutrient retention properties of internally porous inorganic amendments in high sand content root zones

Internally porous inorganic amendments (IPIA’s) are thought to improve water and nutrient retention of root zones. This study examined the performance of three amendment materials, a cla-cined clay and two diatomaceous earth products when added to high sand root zone mixes. Water retention aspects focused on the capacity of these materials to retain water and the soil water pressure head where water within the internal pore space is released. Nutrient retention aspects focused on the root zone mix CEC, selectivity of K vs. Ca on exchange sites, and impact of these characteristics on nutrient leaching. All IPIA’s retained water in the internal porosity, yet diatomaceous earth materials contained a larger proportion internally than calcined clay. The diatomaceous earth products also released water from the internal pore space at slightly less negative pressure heads than clacined clay. Yet, all IPIA’s released water from the internal pore space at relatively low soil water suction. All IPIA’s exhibited selectivity for K vs. Ca on exchange sites. Only the calcined clay contained sufficient CEC to translate this selectivity into a K retention response. Thus, mixes containing calcined clay showed the greatest delay in K elution from column leaching experiments.