Using Composted Cow Manure to Improve Nutrient Content, Aeration Porosity, and Water Retention of Pine Bark-Based Potting Media

Composted cow manure (CCM) was used as a potting media amendment. A common base mix of 8 parts pine bark and 1part sand was compared with 3 other mixes that contained 20%, 30%, and 40% compost (v/v). The plant nutrient concentrations of the base mix and the three CCM-base mix blends were compared with major plant nutrient concentrations provided by fertilizing the base mix with a common granular fertilizer. It was found that adding compost to the mix could replace a portion of the P2O5, all of the K2O and about half of the nitrogen. The aeration porosity, total porosity, volumetric water holding capacity and bulk density of the four mixes were measured. The results indicated that mixing CCM with the base mix made a substantial improvement in the aeration porosity, total porosity, water holding capacity, and density. Water retention curves (WRCs) were developed using the dewpoint method for the four mixes with high levels of correlation. The R2 values for the four fitted curves ranged from 0.87 to 0.94. The results indicated that the 40% CCM mix provided the best amount of readily available water for a plant. It was concluded that mixing CPM with a bark-sand base mix has the potential to reduce the need for non-renewable ingredients, such as peat moss, and to reduce fertilizer costs for a commercial nursery. The study delivers a template to prepare and analyze soil-like substrates regarding their WRCs using the dew point method.