Glenn B. Fain

Nitrogen Immobilization in Plant Growth Substrates: Clean Chip Residual, Pine Bark, and Peatmoss

Rising costs of potting substrates have caused horticultural growers to search for alternative, lower-cost materials. Objectives of this study were to determine the extent of nitrogen immobilization and microbial respiration in a high wood-fiber content substrate, clean chip residual. Microbial activity and nitrogen availability of two screen sizes (0.95 cm and 0.48 cm) of clean chip residual were compared to control treatments of pine bark and peatmoss in a 60-day incubation experiment. Four rates (0, 1, 2, or 3 mg) of supplemental nitrogen were assessed. Peatmoss displayed little microbial respiration over the course of the study, regardless of nitrogen rate; followed by pine bark, 0.95 cm clean chip residual, and 0.48 cm clean chip residual. Respiration increased with increasing nitrogen. Total inorganic nitrogen (plant available nitrogen) was greatest with peatmoss; inorganic nitrogen in other treatments were similar at the 0, 1, and 2 mg supplemental nitrogen rates, while an increase occurred with the highest rate (3 mg). Clean chip residual and pine bark were similar in available nitrogen compared to peatmoss. This study suggests that nitrogen immobilization in substrates composed of clean chip residual is similar to pine bark and can be treated with similar fertilizer amendments during nursery production.

ADDITION OF PULP MILL ASH RAISES PH, MODIFIES PHYSICAL PROPERTIES, AND ALTERS YOUNG TOMATO PLANT GROWTH AND MINERAL NUTRITION IN A PEAT-BASED SUBSTRATE

Pulp and paper mills often burn wood waste to fuel their boilers. The ash from a Mississippi pulp mill boiler was evaluated for potential use as an amendment to peat moss-based greenhouse substrates for production of young tomato plants. Between 0 and 50% ash was added to a custom-blended peat moss-based substrate, and these were compared to a commercially available substrate without ash. Addition of ash increased substrate pH, conductivity (EC), bulk density and water holding capacity, while reducing airspace and average particle size. In general, tomato plants grown in 0–40% ash had similar growth indexes as plants grown in commercial substrate. Increasing amounts of ash decreased tomato shoot nitrogen (N), potassium (K), iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) concentration, and increased concentrations of phosphorus (P), calcium (Ca), sulfur (S), and boron (B). These results indicate that pulp mill ash has the potential to be used as a substrate component for greenhouse container production of tomato.

Species and Media Effects on Soil Carbon Dynamics in the Landscape.

Three woody shrub species [cleyera (Ternstroemia gymnanthera Thunb. ‘Conthery’), Indian hawthorn (Rhaphiolepis indica L.) and loropetalum (Loropetalum chinensis Oliv.‘Ruby’)] were container-grown for one growing season in 2008 using either pinebark (industry standard), clean chip residual or WholeTree (derived by-products from the forestry industry) as potting substrates and then transplanted into the landscape in 2008. An Automated Carbon Efflux System was used to continually monitor soil CO2 efflux from December 2010 through November 2011 in each species and substrate combination. Changes in soil carbon (C) levels as a result of potting substrate were assessed through soil sampling in 2009 and 2011 and plant biomass was determined at study conclusion. Results showed that soil CO2-C efflux was similar among all species and substrates, with few main effects of species or substrate observed throughout the study. Soil analysis showed that plots with pinebark contained higher levels of soil C in both 2009 and 2011, suggesting that pinebark decomposes slower than clean chip residual or WholeTree and consequently has greater C storage potential than the two alternative substrates. Results showed a net C gain for all species and substrate combinations; however, plants grown in pinebark had greater C sequestration potential.

Weed Growth and Efficacy of PRE-Applied Herbicides in Alternative Rooting Substrates Used in Container-Grown Nursery Crops

Abstract Container-grown nursery crops in the southeastern United States are typically grown in a rooting substrate comprised primarily of the ground bark of pine trees. However, pine bark is becoming less available and more costly because of changes in production and marketing practices within southeastern pine forestry. This shortage has resulted in the economic incentive to seek pine bark alternatives. Two possible alternatives are clean chip residual and whole tree. These alternatives are like pine bark, because both are products of southern pine forestry. Unlike pine bark, which is a single part of the tree, these alternatives contain all parts of the tree, including wood and foliage in various portions. Registration of preemergence-active herbicides has been based solely upon data obtained from pine bark–based nursery production. Research was conducted to determine if the control of (1) large crabgrass with prodiamine, (2) eclipta with flumioxazin, and (3) spotted spurge with isoxaben would be comparable in these alternatives to what has been established in pine bark. Seed germination of all three weed species in no-herbicide controls was approximately 10% and equivalent between pine bark and the alternatives. Foliage fresh weight production of large crabgrass and spotted spurge was less in the alternatives compared to pine bark; eclipta was not affected. For all three weed species–herbicide combinations, weed control was nearly identical between pine bark and the alternative substrates, provided the herbicide had been applied at its registered rate. For all three herbicides, rates that are effective in pine bark substrates will be equally effective in the pine bark alternatives. Nomenclature: Flumioxazin; isoxaben; prodiamine; eclipta Eclipta alba (L.); large crabgrass Digitaria sanguinalis (L.) Scop.; spotted spurge Chamaesyce maculata (L.) Small.

Polymeric resins adsorb and release oryzalin in response to pH

Abstract Two polymeric anion-exchange resins and one sorbent resin were evaluated for their propensity to adsorb, and subsequently desorb, oryzalin. The intent was to determine whether these resins could adsorb and subsequently release oryzalin in a manner that would render these resins as an option for slow-release herbicide delivery. The dinitroaniline herbicide oryzalin is weakly acidic with a dissociation constant (pKa) of 8.6. An additional objective was to determine whether altering the pH between sorption and desorption would enhance the desired performance. Maximum oryzalin sorption by the two anion-exchange resins was between 127 and 132 mg g−1 ai. The sorbent resin was adsorbed at a maximum concentration of 191 mg g−1 ai. Maximum sorption occurred with the pH 10 solutions with all resins. Average oryzalin desorption by the anion-exchange resin was between 0.12 and 3.84 mg g−1 per desorption event. Maximum desorption occurred at pH 6.0. Results reveal that the resins evaluated may have merit for slow-release herbicide delivery. Nomenclature: Oryzalin.