Jeff L. Sibley

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.

COMPARISON OF THREE CONTROLLED-RELEASE NITROGEN FERTILIZERS IN GREENHOUSE CROP PRODUCTION

Controlled-release nitrogen fertilizers allow growers to reduce nitrogen loss from leaching in comparison to soluble formulations. Plant growth and nitrogen leaching during greenhouse production of Begonia   ×   semperflorens-cultorum Hort. cv. “Brandy” (Begonia), Euphorbia pulcherrima Willd. ex Klotzch cv. “Freedom Red” (Poinsettia), Ficus benjamina L., and Nephrolepis exaltata (L.) Schott cv. “Bostoniensis” (Boston Fern) were evaluated for eight weeks using three commercial controlled-release nitrogen fertilizers in combination with phosphorus and potassium sources to maintain a 3 : 2:1 NPK ratio. Mini Polymer Coated Urea (MPCU) 41-0-0, Trikote 42-0-0, and Regalite Nitroform (RN) 38-0-0 were incorporated into the substrate at rates of 0.9 kg nitrogen (N) m−3 and 1.5 kg N m−3 prior to potting. Total soluble salts in the leachates reflected the initial leaching of salts from the substrate, some increase or maintenance of salt levels through the third week, and lower levels from the fourth through eighth weeks. The high and low rates of Trikote and the high rate of MPCU provided acceptable levels of NH4 + for production purposes through the fourth or fifth week, the low rate of MPCU provided low levels through the third week and minimal levels thereafter, while both levels of RN showed progressive decreases from the outset. NO3 − levels varied within treatments during the eight-week period, with levels suitable for production observed during the trial with MPCU and Trikote, and declining to low levels with RN. Growth indices were similar among treatments, with the exceptions of Begonia and Poinsettia, which were larger with a low rate of RN 40 days after potting (DAP). Begonia was also larger with a low rate of Trikote 40 DAP. Shoot fresh weights (SFW) of Begonia and Poinsettia were higher with a low rate of Trikote than with MPCU or RN 40 DAP, and higher for Poinsettia with low rates of both MPCU and Trikote compared to RN 57 DAP. SFW and shoot dry weights (SDW) were similar among treatments with Boston Fern and Ficus benjamina.

EFFECT OF CURRENT FERTILIZATION PRACTICES ON NUTRITIONAL STATUS OF DOUBLE-CROPPED TOMATO AND CUCUMBER PRODUCED WITH PLASTICULTURE

When vegetables are double-cropped on polyethylene mulch, fertilizer recommendations for each crop may need to be adjusted because liming and preplant applications are done prior to laying plastic. When current fertilizer recommendations for single crops were used for cucumber following tomato, the cucumber plants looked like green, indicating a nitrogen (N) and/or potassium (K) deficiency was developing, suggesting that nutrient availability for the second crop was not adequate for producing the highest yields. Therefore, the nutritional status of both crops was diagnosed using sufficiency range data and DRIS norms to determine which nutrient(s) was limiting crop nutrition. Regardless of N source used as a sidedress injection material (at a rate of 7 kg N ha−1wk−1 as ammonium nitrate or calcium nitrate) or liming material used to adjust soil pH to 6.5 (carbonate- or oxide-based calcitic or dolomitic lime), foliar levels of N and K, and possibly phosphorus (P) were found to be limiting factors according to sufficiency range data and DRIS norms. This study suggests that current fertility recommendations for tomato and cucumber grown as single crops in Alabama need to be reevaluated for double crops.

Nitrogen Requirements for Sweetpotato Following a Crimson Clover Cover Crop

Sweetpotato [Ipomoea batatas (L.) Lam.] is an economically important crop in the southeastern United States, and sustainable production practices that include reducing fertilizer costs and improving soil organic matter are needed. Field studies were conducted in the Spring of 2007 and 2008 to evaluate nitrogen fertilization requirements of sweetpotato. Treatments of 0, 50, and 101 kg·ha−1 nitrogen (from ammonium nitrate applied preplant broadcast) were applied following a crimson clover (Trifolium incarnatum L.) cover crop along with a conventional no cover crop treatment using 101 kg·ha−1 N (from ammonium nitrate). Sweetpotato yields for all rates of N fertilizer following the cover crop were similar (for ‘Beauregard’ in 2007) or greater (for ‘Xushu 18’ in 2008) than yields from plants grown using the conventional treatment. Percentage of dry matter of storage roots was not affected by treatment. Nitrogen fertilization can be reduced or eliminated when sweetpotatoes are produced following a crimson clover winter cover crop.

Effect of Runner Plantlet Size on Performance of Strawberry Plug Plants

Abstract Size of plantlets used in propagation of strawberry plug plants did not affect yield or berry size. Daughter plants containing one to three compound leaves may be used in propagation. Plant size in this study was determined by petiole length to provide a simple grading method with easy application to the industry. Although no significant differences were identified among the three size classes evaluated in this “length based” study, plantlet size might affect eventual yields if sizes were determined by fresh weight or leaf area. Future studies in this area are warranted. Transplant survival should also be considered in future studies to determine whether particular sizes offer an advantage of lower mortality in the greenhouse, or if field survival is different among plants which differ in size at the initiation of propagation.

Mixed Municipal Solid Waste Compost as a Soil Amendment on Yield and Heavy Metal Accumulation in Okra and Watermelon

ABSTRACT Application of compost in horticultural crops has the potential to provide many benefits and yet there are concerns regarding accumulation of heavy metals in the crop and on human health. Effects of amending soil with compost made from mixed municipal solid waste (MSW) on yield of okra (Abelmoschus esculentus L.) and watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] and on heavy metal concentrations (Cd, Cu, Cr, Ni, Pb, and Zn) in pods of okra and pulp and juice of watermelon were investigated. Four MSW compost rates were applied, 25, 50, 75, and 100 Mg·ha−1, and compared to a non-amended control with no compost application. Addition of MSWC increased yield of okra and weight of watermelons over the control. There were no differences among treatments in heavy metal concentrations in okra pods, watermelon pulp, or juice.

Diuron Sorption by Pine-Bark Substrate and Foliar vs. Root Absorption by Yellow Woodsorrel (Oxalis stricta)1

Postemergence-applied diuron effectively controls yellow woodsorrel in nursery crops grown in pine bark–based container substrate. Whether the phytotoxicity of diuron on yellow woodsorrel is exclusively the result of foliar activity or is partially the result of root-based activity has not been determined. Application in which diuron was allowed to contact both the foliage and the pine bark–based substrate provided 84% control as determined by shoot fresh-weight reduction relative to that of a nontreated control. Foliar-only and root-only applications provided 52 and 12% shoot fresh-weight reduction, respectively. Absorption and translocation of foliar-applied diuron by yellow woodsorrel was evaluated using radiotracer techniques. After 24 h, 86% of the applied diuron had been absorbed, and 76% of the amount applied remained in the treated leaflet, indicating minimal translocation. Diuron sorption by the pine bark–based substrate was evaluated using radiotracer techniques. After 3 h, less than 6% of applied diuron remained in the aqueous phase, indicating 94% sorption. Exposing yellow woodsorrel roots to diuron concentrations as low as 0.50 mg/L resulted in injury, and concentrations equal to or greater than 10 mg/L resulted in death. Calculations described herein indicate the concentration that probably would occur within the aqueous solution held within the substrate following a 1.12-kg ai/ha application is sufficient to be phytotoxic to yellow woodsorrel. Thus, root-based absorption is a contributing factor in the overall efficacy of postemergence-applied diuron in controlling yellow woodsorrel. Nomenclature: Diuron; yellow woodsorrel, Oxalis stricta L. #3 OXAST. Additional index words: Herbicide translocation, soil sorption. Abbreviations: ANOVA, analysis of variance; PPFD, photosynthetic photon flux density; WAT, weeks after treatment.

Laboratory and Greenhouse Evaluation of Quicklime Sources for Suitability as Agricultural Liming Materials

Abstract Quicklime or burnt lime (CaO), is a highly soluble liming material recognized as an acceptable means for neutralization of acid soils in the United States. Blending CaO and MgO with agricultural lime (CaCO3) may prove an alternative to ground agricultural limestone for raising soil pH and providing fertilizer Ca and Mg for crop growth. The objectives of this study were to determine the chemical properties of several CaO, MgO, and CaCO3 liming blends compared to carbonate limestones, and analyze their respective effects on soil solution chemistry and shoot yield of a sorghum-sudangrass hybrid grown under greenhouse conditions. Three formulations of oxide liming materials (CaO, CaO + CaCO3, and CaO + MgO + CaCO3) were evaluated in the laboratory to determine their respective effectiveness as soil amendments compared to two dolomitic limestones (ground and pelletized) and reagent-grade calcium hydroxide [Ca(OH)2]. A 150-day incubation study was conducted to determine the effects of liming materials on soil pH and extractable nutrients, and a greenhouse study was completed to observe the effects of liming materials and rates on the herbage yield of a sorghum-sudangrass hybrid. Oxide liming materials averaged higher calcium carbonate equivalence (CCE) than ground and pelletized dolomitic limestones. An incubation study found CaO, CaO + CaCO3, and CaO + MgO + CaCO3 resulted in rapid pH adjustments (from pH 4.1 and 4.4 to 6.0 +) at one day after test initiation for two soil types and gave higher mean pH values than carbonate limes when applied at equivalent rates based upon CCE. Oxide liming materials also resulted in higher concentrations of soil extractable calcium (Ca) and magnesium (Mg), and the use of all liming materials, regardless of chemical form, alleviated Al toxicity. In a nine week greenhouse bioassay, all oxide liming materials and reagent-grade Ca(OH)2 were applied at 1/2X, 1X, and 2X the recommended application rate of ground dolomitic limestone based on CCE, resulting in similar or higher shoot yields comparatively at conclusion of this study. Because oxide liming materials have higher CCE values and provide more water-soluble sources of fertilizer Ca and Mg compared to ground and pelletized limestone, producers have potential for obtaining a more complete neutralization of acid soil conditions and shoot yields similar to or higher than those obtained with dolomitic limestone, using less material in the process. This study did not determine if changes in current liming practices would result in reductions of total fertilizer costs per year using oxide limes in place of carbonate forms.

EFFECT OF LIMING MATERIALS ON SOIL AVAILABLE NUTRIENTS, YIELD, AND GRADE DISTRIBUTION OF DOUBLE-CROPPED TOMATO AND CUCUMBER GROWN WITH PLASTICULTURE

For economical reasons, cucumber (Cucumis sativus L.) may be grown as a double crop after tomato (Lycopersicon esculentum Mill.). In this production system, plant nutrition may be limited for the second crop due to pH change or insufficient levels of calcium or magnesium. The objective of this 2-year field study was to compare the effects of selected liming materials on yield and grade distribution, and soil available nutrients of a tomato/cucumber double crop produced with plasticulture. Liming materials were compared to a control and a CaSO4 treatment based on the same neutralizing value as standard agricultural limestone. Supplemental N fertilization was provided by weekly injections at a rate of 7 kg/ha/week from ammonium nitrate (NH4NO3) or calcium nitrate [Ca(NO3)2]. Each year, soil samples were collected at the beginning of the study and after each crop to determine nutrient availability. All liming materials raised soil pH in 1998 and 1999 over the unlimed control, though not to the target level for tomato and cucumber production (pH 6.5). Throughout the study, agricultural limestone, a high CaO-containing blend (calcitic blend) and a CaO/MgO (dolomitic blend), resulted in greater fruit weights compared to the control and CaSO4. These materials, along with quick lime (CaO), provided higher levels of soil Ca and Mg available for plant growth. However, it was found that current recommendations for potassium (K), regardless of liming source, were not adequate for optimal soil reserves and yields in this tomato/cucumber cropping system. Ammonium nitrate as a source of N for fertilization was as effective as Ca(NO3)2.

English Ivy (Hedera helix) Control with Postemergence-Applied Herbicides

Abstract English ivy (Hedera helix) is an evergreen, perennial vine that was introduced from Europe and Asia and is not endemic in much of the United States. English ivy can be invasive and difficult to control once established. Four similar, but not identical, experiments were conducted in sequence to evaluate selected, POST-applied herbicides for English ivy control. English ivy plants were propagated from cuttings and container-grown to obtain a large population of uniform plants. Aminopyralid and fluroxypyr applied at 1.34 and 0.71 kg ae ha−1, which is more twice the maximum registered rate for either herbicide, were ineffective. Glyphosate and 2,4-D amine were generally more effective, but neither herbicide provided a level of control that could be deemed consistently acceptable. Glyphosate applied at 8.51 kg ae ha−1 (the highest rate evaluated) provided 69, 98, and 89% control in the second, third, and fourth experiments as determined by foliage fresh-weight reduction relative to a nontreated control. Treatment with 2,4-D at 5.60 kg ae ha−1 (the highest rate evaluated) controlled English ivy 28, 98, and 89% in the second, third, and fourth experiments, respectively. Mixtures of 2,4-D and glyphosate were generally no more effective than were the components applied alone. Metsulfuron was the most effective herbicide. Metsulfuron applied at 0.168 kg ai ha−1 controlled English ivy ≥ 97% across the three experiments in which this treatment was included. This treatment also prevented regrowth. Nomenclature: 2,4-D, aminopyralid, fluroxypyr, glyphosate, metsulfuron, sulfometuron, English ivy, Hedera helix L Management Implications: English ivy was first introduced into North America centuries ago in the colonial period. This species has been widely planted as an ornamental ground cover, but it can be invasive and difficult to control once established. Herbicide-based control has traditionally been only marginally effective, and eradication was never attainable. Six herbicides, plus two herbicide combinations were evaluated for English ivy control. Surprisingly, two relatively new pyridine herbicides that are used for the control of noxious and invasive species in pastures and rangelands, i.e., aminopyralid and fluroxypyr, were less effective than either glyphosate or 2,4-D. The sulfonylurea herbicides metsulfuron and sulfometuron were also evaluated. Metsulfuron was more effective than sulfometuron and was also more effective than either glyphosate or 2,4-D. Metsulfuron applied at 0.168 kg ai ha−1 consistently provided ≥ 97% control, as measured by foliage fresh-weight reduction, and prevented any regrowth. Metsulfuron may have potential for English ivy control and eradication.