Evaluating Anaerobically Digested Dairy Fiber as a Substitute for Peat in Container Production and Nutrient Availability from Organic Fertilizers and Amendments

The purpose of this research was to investigate alternative, renewable materials for potted plant production. Sphagnum peat moss has been a primary component of soilless potting media for decades. Concerns over the sustainability of harvesting peat have fostered a search for renewable media components. Anaerobically digested dairy fiber (ADDF), a byproduct of methane production, shows promise as an alternative to peat. A variety of representative floriculture and nursery crops were grown in a numerous ADDF-containing media to evaluate its suitability as a substrate component. Nutrient leaching was monitored to evaluate the potential for environmental impact of using ADDF. Physical properties were not significantly different between greenhouse and nursery mixes with and without ADDF. Greenhouse mixes that replaced 50% of peat with ADDF mostly produced plants of equal quality and size of those grown in a control mix. There was not difference between nursery crops grown in a mix with all peat replaced with ADDF and a control mix. Plants grown in ADDF-containing mixes had higher tissue P concentrations than those grown in mixes without ADDF. ADDF containing mixes leach a significant amount of phosphorus over several weeks. Anaerobically digested dairy fiber can be used as a media component for a variety of floriculture and nursery crops and supplies a significant amount of plant available P. Nutrient leaching should be considered when using ADDF in media. Switching to an organic fertilization regiment is one of the greatest obstacles greenhouse growers face in adopting organic practices. Nutrient availability from organic sources is difficult to predict. Greenhouse crops grown using a combination of organic fertilizers generally often have better results than those grown using only one organic fertilizer. Incubation trials with unplanted media were conducted to monitor nutrients leached and changing nutrient forms over time. A variety of liquid organic fertilizers (LF), organic pre-plant incorporated organic fertilizers (PPIF), vermicompost and combinations of fertilizers were incorporated into a peat-perlite potting mix. Media was stored at 25°C. Leachate and saturated media extracts (SME) samples were taken to evaluate nutrient quantity and transformations, respectively. Mixtures of fertilizers produced many significant interactions over time indicating that organic fertilizers have different nutrient release patterns over time. Most nutrients are leached within the first four leaching events. Cumulative phosphorus leached as a percentage of phosphorus incorporated in the media varied greatly between fertilizers. Combinations of LF and PPIF slowed nitrification in SME samples. Vermicompost acts much like a PPIF in media. Numerous factors affect nutrient availability from organic sources