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- Author or Editor: James C. Locke x
A series of column studies were conducted to determine the influence of three different biochar types on nitrate, phosphate, and potassium retention and leaching in a typical greenhouse soilless substrate. A commercial substrate composed of 85 sphagnum peatmoss : 15 perlite (v:v) was amended with 10% by volume of three different biochar types including: gasified rice hull biochar (GRHB), sawdust biochar (SDB), and a bark and wood biochar (BWB). The non-amended control substrate, along with substrates amended with one of three biochar materials, were each packed into three columns. Columns were drenched with nutrient solution and leached to determine the impact of biochar on nutrient retention and leaching. Nitrate release curves were exponential and peaked lower, at later leaching events, and had higher residual nitrate release over time with each biochar amendment. The impact of biochar amendment on phosphate retention and release was more variable within and across the two experiments. In both experiments, the GRHB was a net source of phosphate, providing more phosphate to the system than the fertilizer application and hence obscuring any retention and release effect it might have. Potassium release varied by amendment type within each experiment, but within each amendment type was relatively consistent across the two experiments. All biochar types were a source of potassium, with GRHB providing more than SDB, but both providing far more potassium than the fertilizer event. The BWB amendment resulted in more leached potassium than the control substrate, but relatively little compared with GRHB and SDB amendments.
Byproducts of pyrolysis, known collectively as biochar, are becoming more common and readily available as ventures into alternative energy generation are explored. Little is known about how these materials affect greenhouse container substrates. The objective of this research was to determine the effect of one form of biochar on the nutrient retention and release in a typical commercial greenhouse container substrate. Glass columns filled with 85:15 sphagnum peatmoss:perlite (v:v) and amended with 0%, 1%, 5%, or 10% biochar were drenched with nutrient solution and leached to determine the impact of biochar on nutrient retention and leaching. Nitrate release curves were exponential and peaked lower, at later leaching events, and had higher residual nitrate release over time with increasing biochar amendment rate. This suggests that biochar might be effective in moderating extreme fluctuations of nitrate levels in container substrates over time. Peak phosphate concentration decreased with increasing biochar amendment rate, whereas time of peak release, girth of the peak curve, and final residual phosphate release all increased with increasing biochar amendment. Additional phosphate levels in leachates from biochar-amended substrates, in addition to the higher phosphate concentrations present in later leaching events, suggest this form of biochar as a modest source of phosphate for ornamental plant production. Although there was not sufficient potassium (K) from biochar to adequately replace all fertilizer K in plant production, increasing levels of this form of biochar will add a substantial quantity of K to the substrate and should be accounted for in fertility programs.
The repellency and toxicity of a petroleum-based proprietary horticultural oil, Sunspray 6E Plus, was tested against the greenhouse whitefly, Trialeurodes vapor-ariorum (Westwood), on greenhouse-grown chrysanthemums [Dendranthema ×grandiflorum (Ramat.) Kitamura cv. Iceberg]. A 2% (v/v) aqueous spray repelled adult whiteflies for at least 11 days after spraying and it was toxic to newly hatched and third stage larval whiteflies. No phytotoxicity was observed when four weekly sprays of 1%, 2%, and 4% oil were applied.
The antifungal properties of a hydrophobic neem (Azadirachta indica A. Juss.) seed extract (clarified neem oil) were tested against three postharvest apple (Malus domestica Borkh.) pathogens—Botrytis cinerea (pers.) ex Fr. (gray mold), Penicillium expansum Thom. (blue mold rot), and Glomerella cingulata (Ston.) Spauld. & Schrenk. (bitter rot). The antifungal activity of neem seed oil also was compared to that of CaCl2. A 2% aqueous emulsion of the clarified neem seed oil was moderately fungicidal to B. cinerea and G. cingulata in inoculated fruit, but bad little activity against P. expansum. Ethylene production was reduced 80% in fruit dipped in 2% neem seed oil compared to wounded, inoculated controls. Neem seed oil was as effective an antifungal agent as CaCl2, but the effects of the two combined were not additive.
Cation exchange capacity (CEC) describes the maximum quantity of cations a soil or substrate can hold while being exchangeable with the soil solution. Although CEC has been studied for peatmoss-based substrates, relatively little work has documented factors that affect CEC of pine bark substrates. The objective of this research was to determine the variability of CEC in different batches of pine bark and determine the influence of particle size, substrate pH, and peat amendment on pine bark CEC. Four batches of nursery-grade pine bark were collected from two nurseries, and a single source of sphagnum moss was obtained, separated in to several particle size classes, and measured for CEC. Pine bark was also amended with varying rates of elemental sulfur and dolomitic limestone to generate varying levels of substrate pH. The CEC varied with pine bark batch. Part of this variation is attributed to differences in particle size of the bark batches. Pine bark and peatmoss CEC increased with decreasing particle size, although the change in CEC from coarse to fine particles was greater with pine bark than peatmoss. Substrate pH from 4.02 to 6.37 had no effect on pine bark CEC. The pine bark batch with the highest CEC had similar CEC to sphagnum peat. Amending this batch of pine bark with sphagnum peat had no effect on composite CEC.
Silicon (Si) is a plant beneficial element associated with the mitigation of abiotic and biotic stresses. Most greenhouse-grown ornamentals are considered low Si accumulators based on foliar Si concentration. However, Si accumulates in all tissues, and there is little published data on the distribution of Si in plants. This knowledge may be critical to using Si to mitigate tissue-specific plant stresses, e.g., pathogens. Therefore, we quantified Si accumulation and distribution in petunia (Petunia ×hybrida Hort. Vilm.-Andr. ‘Dreams Pink’), a low Si accumulator, and sunflower (Helianthus annuus L. ‘Pacino Gold’), a high Si accumulator. Plants were grown in a sphagnum peat: perlite substrate amended with 0% (−Si) or 20% (+Si) parboiled rice hulls for 53 (petunia) or 72 days (sunflower). Aboveground dry weight was greater in nonamended petunia (13%) and sunflower (18%), compared with rice hull–amended plants, but days to flower was unaffected. Sunflowers grown in the rice hull–amended substrate had the greatest Si concentration in leaves (10,909 mg·kg−1), whereas roots (895 mg·kg−1), stems (303 mg·kg−1), and flowers (252 mg·kg−1) had lower, but similar Si concentrations. In petunia, Si concentration was greatest in leaves (2036 mg·kg−1), then roots (1237 mg·kg−1), followed by stems (301 mg·kg−1), and flowers (247 mg·kg−1). The addition of rice hulls to the substrate increased Si concentration in sunflower 414% in roots, 512% in flowers, 611% in stems, and 766% in leaves. By contrast, Si concentration in petunia increased only 7% in flowers, 105% in stems, and 115% in leaves, but increased 687% in roots. In rice hull–amended sunflowers, the distribution of Si was 91% in leaves, 3% in stems, 3% in roots, and 3% in flowers, and in petunia, it was 72% in leaves, 17% in stems, 6% in roots, and 5% in flowers.
Nitrogen (N) fertilization recommendations to achieve optimum growth are well established for many floriculture crops. Although it has been shown that plant functions can recover from N deficiency in other crops, little research has investigated the threshold beyond which a bedding plant crop is recoverable. The objective of this research was to determine the effect of N deficiency on geranium chlorophyll content and growth and then to document the degree of recovery and recovery time from N deprivation. This was determined in two experiments by monitoring chlorophyll content and growth of seedlings grown in hydroponic culture in which the N source was removed and then restored after differing lengths of time. Summarizing across both experiments, chlorophyll and foliar N levels were shown to rebound quickly after N deprivation; however, growth was reduced after just 4 days compared with plants fed constantly. Geraniums grown without N for 4 to 12 days resulted in smaller, more compact plants with lower shoot–to-root ratios. Although foliar chlorophyll and N concentration recovered from longer periods in N growth solution, geranium growth was reduced and failed to completely recover for any plant receiving more than 2 days of N-free solution.
Geranium (Pelargonium ×hortorum) is considered to be one of the top-selling floriculture plants, and is highly responsive to increased macro- and micronutrient bioavailability. In spite of its economic importance, there are few nutrient disorder symptoms reported for this species. The lack of nutritional information contributes to suboptimal geranium production quality. Understanding the bioenergetic construction costs during nutrient deficiency can provide insight into the significance of that element predisposing plants to other stress. Therefore, this study was conducted to investigate the impact of nutrient deficiency on plant growth. Pelargonium plants were grown hydroponically in a glass greenhouse. The treatment consisted of a complete modified Hoagland's millimolar concentrations of macronutrients (15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S) and micromolar concentrations of micronutrients (72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo) and 10 additional solutions each devoid of one essential nutrient (N, P, Ca, Mg, S, Fe, Mn, Cu, Zn, or B). The plants were photographed and divided into young, maturing, and old leaves, the respective petioles, young and old stems, flowers, buds, and roots at “hidden hunger,” incipient, mid- and advanced-stages of nutrient stress. Unique visual deficiency symptoms of interveinal red pigmentation were noted on the matured leaves of P- and Mg-deficient plants, while N-deficient plants developed chlorotic leaf margins. Tissue N concentration greatly influenced bioenergetic construction costs, probably due to differences in protein content. This information will provide an additional tool in producing premium geraniums for the greenhouse industry.
Currently, formulation of inorganic fertilizers is based on cation amounts such as NH4, K, Mg, Ca, Fe, MN Cu, and Zn, whereas anion species and amounts are viewed, with few exceptions, as necessary fillers. The delivery of cations in the nutrient solution is associated with an anion such as Cl, SO4, NO3, PO4 or CO3. These anions at higher concentrations can result in different growth responses by altering the rhizosphere pH, soluble salts, and influencing the uptake of both cations and anions. The impact of these anions has not been extensively studied in the formulation of inorganic fertilizers. Several experiments assessed the effect of SO4 and Cl on root and shoot growth and development of bedding plants represented by petunia, impatiens, and vinca. In all treatments, plant height, shoot and root dry weight, and flower number decreased with an increase in Cl concentration. Root morphology was marked by fewer total roots and shorter primary and secondary roots when grown with Cl anions compared to the plants grown with SO4 anions. This indicates that anions have a larger role in determining optimum fertilizer formulation than previously believed. This information provides an additional tool in formulating fertilizers for greenhouse bedding plant production.
There are several commercial materials available that have remarkable hydrating properties and many claim them to be ideal for use in horticulture and deliver water to the roots better than other soilless media. These are often referred to as “hydrogels.” There is general agreement in the literature that the physical characteristics of hydrogels are altered in the presence of divalent cations such as Ca and Mg. Tap water can reduce the water holding capacity by 70% or more. Unfortunately, the literature agrees on little else in terms of the performance of hydrogels. Some of the confusion is caused in part by comparing one type of hydrogel to another but treating all as equal. There has been no mathematical performance evaluation of hydrogel and what affect the environment may play in that performance to predict potential irrigation savings or shelf life extension. In a series of greenhouse and laboratory studies, we have evaluated the physical characteristics of several types of hydrogels and characterized bedding plant performance throughout a typical growth cycle. We measured leaf expansion, water content of the media, root growth, flowering, and fresh and dry masses. We have found little to no differences in the rate of leaf expansion when using hydrogels, but enhanced root growth early in production with the hydrogels. Our results indicated that plant growth was enhanced early in production, but any advantage they may have was lost by the end of production. Plants grown in hydrogels needed irrigation less frequently than those without hydrogel, but the effect was diminished over time. Since the use of the material can add about 15% to the cost of potting media, this data is designed to assist growers in hydrogel use and to determine any benefits of the added costs.