Chemical, physical, and moisture release characteristics of compost based potting media

A commercially available composted cow manure was used as a potting media amendment. A common base mix for woody ornamentals of 8 parts pine bark and 1 part sand was compared with 3 other mixes that contained 20%, 30%, and 40% compost (v/v). The remaining fraction of these three mixes was the base mix (bark and sand). Samples of the pine bark and compost were analyzed to determine the following plant nutrients and mineral concentrations: nitrogen (organic and soluble), carbon, P2O5, K2O, Ca, S, Mg, Mn, Cu, Zn, Na, Fe, and Al. The chemical characteristics of the three compost-based potting media mixes were calculated on a mass basis. The aeration porosity, total porosity, volumetric water holding capacity and bulk density of the four mixes were measured using a chamber that was constructed to facilitate measurement of the physical properties of potting media. The results indicated that increasing the percentage of compost in potting media caused the desired decrease in aeration porosity, and total porosity. The data of moisture release curve was obtained using the pressure plate and dew point methods. The results indicated that the 20% compost potting media mix had the lowest refill point, the 30% compost potting media mix could hold most water at the wilting point, and the 40% compost potting media mix had the largest range of readily available water. Including compost in potting media created a substantial increase in valuable plant nutrients and minerals. It was concluded that adding 20% to 30% compost to a screened bark base mix would provide the majority of the improvements in fertilizer value, physical properties, and mass of water in a container for a growing plant.