Plant Performance and Nutrient Losses during Containerized Bedding Plant Production Using Composted Dairy Manure Solids as a Peat Substitute in Substrate

Recent concerns over the environmental impact of peat harvesting have led to restrictions on the production of peat in Florida and other areas. The objectives of this study were to evaluate the use of composted dairy manure solids as a substitute for sphagnum or reed-sedge peat in container substrates on the growth of Solenostemon scutellarioides L. Codd 'Wizard Velvet', Tagetes panda L. 'Safari Queen', and Begonia x hybrida 'Dragon Wing Red' and to examine the nutrient content in leachate from pots. Plants were grown for 5 weeks in a greenhouse in 15-cm plastic pots with seven substrates containing various proportions of sphagnum peat (S) or reed-sedge peat (R) and composted dairy manure solids (C), each with 20% vermiculite and 20% perlite. Substrate composition had no effect on plant quality ratings, number of flowers, or root dry mass for any of the plant species evaluated. Substrate composition did not affect the growth index (GI) or shoot dry mass of S. scutellarioides 'Wizard Velvet' or the GI of T. panda 'Safari Queen'. However, growth of B. xhybrida 'Dragon Wing Red' (GI and shoot dry mass) and T. panda 'Safari Queen' (shoot dry mass only) was highest in the 35:OR:0C substrate. The substrates containing sphagnum peat and/or composted dairy manure solids (3S:OR:0C, 25:OR:1C and 1S:OR:2C) had the highest NH4-N losses through the first 7 d of production. The 0S:3R:OC substrate had the highest initial leachate NO3+NO2-N losses and this trend persisted throughout most of the production cycle. Significantly more dissolved reactive phosphorus was leached from substrate mixes containing composted dairy manure solids than mixes containing only sphagnum or reed-sedge peat materials through 19 d after planting. All substrates tested as part of this study appeared to be commercially acceptable for production of container-grown bedding plant species based on plant growth and quality. However, nutrient losses from the containers differed depending on the peat or peat substitute used to formulate the substrates.