Jason Smith and Jeff Gillman
During the past few months, there have been several research papers published in scientific
journals that are relevant to the nursery industry of
· Most commercial potting mixes used today contain at least some peat as a major component. These peat-based mixes are often more acidic than is optimum for the growth of many plants, especially those that thrive in more alkaline conditions. Certain chemicals are recommended for raising the pH of acidic media including: nitrate based soluble fertilizer, Ca(OH)2, CaCO3, KOH, and KHCO3. In the study reported here, Bishko et al. systematically quantified the pH-response of a peat-based medium to the application of chemicals routinely used to raise potting soil pH. The medium used was a 70 peat: 30 perlite medium mixed with a pre-plant nutrient charge, a wetting agent, and between 0 and 1.5 kg/m3 of a dolomitic hydrated lime. This resulted in six different medium pHs between 3.4 and 6.4. The following chemicals were added as a single drench at a rate of 60 mL per 126 mL container: Ca(OH)2, 2.5 to 40 mL/L-1 of a flowable dolomitic limestone suspension, 99.5% KHCO3 between 0.6 and 9.6 g/L-1, 85% KOH between 0.056 and 0.56 g/L-1, 15N-0P-12K water soluble fertilizer at 50-400 mg/L-1 N, and a distilled water as a control. The results indicate that all chemicals are capable of raising medium pH in one day and the pH remained stable except for Ca(OH)2. The most dramatic effect was measured for media that were treated with either flowable dolomitic limestone or KHCO3 and there was a greater effect for lower starting ph media treated with KHCO3. These results suggest that proper selection and use of pH-raising chemicals can lead to more efficient pH treatment and less waste of these chemicals. However, more studies are needed to establish what affects these treatments may have on nutrient uptake and availability. 1
· The use of recycled newspaper as an amendment to container media is the subject of the experiments reported here. Glenn et al. conducted two experiments to evaluate recycled newspaper products as nutrient filters in the bottom of containers. In experiment 1, the authors placed three paper products (ground paper, paper crumble, and paper pellets) 2 or 3 cm deep in 16.5 cm top containers planted with poinsettia plants such that the drainage holes were covered. No paper was added to control containers. The leachate was collected at the first irrigation after fertilization. In experiment 2, the authors placed either paper crumble or paper pellets 2.5 cm deep in the bottom of 16.5 cm top containers (no paper served as controls). Poinsettia plants were grown in these containers and fertilized with 500 mg/L-1 N from Peter’s 20N-4.3P-16.6K once weekly or 200 mg/L-1 N 2 to 3 times per week. In experiment 1, leachate of nitrate and ammonium was reduced by 84% (compared to controls) for the paper pellets. The paper pellets placed 3 cm deep retained up to 732 mg of nitrogen per container. In experiment 2, paper crumble resulted in a reduction of nitrate and ammonium leachate by 100% and 94% 6 days after planting and 57% and 50% 25 days after planting compared to no paper controls. Paper pellets resulted in retention of 776 mg of nitrogen per container in experiment 2. Shoot dry weights were lowest in both experiments when paper pellets were used in the bottom of the containers. These results indicate that the use of recycled newspaper can be a effective means of reducing nitrogen leaching (as measured by nitrate and ammonium leachate) in container nursery production. Certainly medium composition and plant type play an important role in determining the leachate quantity and further work is needed to determine how recycled paper can be best used to reduce leaching for other species and different media mixtures.2
· Many recommendations for seed germination have strict salinity requirements. Specifically, germination is generally best when inorganic salt concentrations are lower. Thus, in the studies reported here, Huang et al. looked at the need for common fertilizer components in pre-plant fertilizers (nitrogen, phosphorus, potassium, and sulphur) for plug seedling growth. In this study, Impatiens wallerana ‘Accent Rose’ and Gomphrena globosa ‘Buddy’ were grown in 288-cell plug trays in a substrate of 3 parts sphagnum moss: 1 part perlite (in two different experiments). Seven different N, P, K and S pre-plant treatments were used (including none, all nutrients at a rate of100 mg/L of substrate, all minus one nutrient for each treatment and N at an additional rate of 50 mg/L of substrate. After planting the plants were treated with soluble fertilizer weekly. The seedlings were then grown to a marketable stage in 48-cell flats. The results indicate that N,P,K and S are all needed for maximum growth. However, since more compact growth is desired, K and S can be eliminated from the pre-plant nutrients since their contribution to growth was small. The better growth form was observed when N was omitted along with K and S, but omitting N alone obtained the best characteristics. This also resulted in very little impact on flowering compared to omission of other nutrients. One drawback is that plants became chlorotic when N was omitted, but the authors found that they turned green quickly after the N was restored. This study indicates that pre-plant salinity requirements can be met by omitting certain previously recommended nutrient components without a major negative effect on the product.3
· Many retail nurseries and garden centers sell birdseed and birdfeeders, especially during the fall and winter. In the report summarized here, authors found that sclerotia, the overwintering structures produced by the plant pathogenic fungus, Sclerotinia sclerotiorum, were observed in commercial sunflower seed bags sold at nurseries for use in birdfeeding. Sclerotinia sclerotiorum is a pathogen that has a very wide host range that includes many important herbaceous perennials, bedding plants and woody ornamentals. In order to determine the frequency of occurrence and the viability of these sclerotia, the authors looked at commercial sunflower seed bags. Ten 1-pound samples representing 10 different bags of commercial sunflower seed were scooped and spread over a hard surface with a light background. The sclerotia were separated from the seeds and counted and weighed. In order to determine the viability of the sclerotia, they were plated on potato dextrose agar and grown for 1 week and examined for characteristic fungal growth. Half of the bags tested contained some sclerotia from as little as 5 (or 0.280 g) to as many as 101 (or 7.47 g) or 1.7%. All sclerotia tested were viable. These results suggest that birdseed, especially sunflower seed, serves as a source of sclerotia. Since birds do not eat the sclerotia, they simply drop the sclerotia to the ground below where they may persist for many years. Once the right conditions are met, the sclerotia produce spores that can infect many different plant species. Nurseries that offer birdseed need to beware of the potential for selling seed containing sclerotia and the potential for spreading this disease to nursery production areas.4
·
Now that soil fumigants such as methyl
bromide are banned by the federal government, alternative methods of soil sterilization
are being sought by many researchers. In the study reported here, Stapleton et
al compared soil solarization techniques in the field
to validate laboratory-derived thermal death dosages of solarization
for common weed species. The survival of
seeds of common weed species (common purslane [Portulaca oleracea],
tumble pigweed [Amaranthus albus], and
black nightshade [Solanum nigrum]) was
determined after treatment. The treatment involved subjecting moist soil (that
was artificially infested with weed seeds) in black polyethylene bags to
double-tent solarization. This resulted in the bags
being subjected to temperatures above 140 oF
at about 1.5 to 2.0 hours after the experiment began. The samples were removed
at different intervals and the experiment was repeated over a two-year period.
In both experiments and after all exposure times, the seeds were effectively
killed (none germinated) in treated soil, but were still viable in untreated
controls. The authors suggest that this
technique will be most effective when smaller containers of soil are treated
and for longer periods of time. This study holds promise for effective soil
sterilization without the use of chemicals. However, the authors do not provide
detailed information on what areas of the country experience enough solar heat
to reach the threshold temperature of 140 oF.
5
1 Bishko, A.J., Fisher, P.R., and Argo, W.R. 2002. Quantifying the pH – response of a
peat-based
medium to application of basic chemicals. HortScience 37(3): 511-515.
2 Glenn, J.S., Gilliam, C.H., Edwards, J.H., Keever, G.J., Knight, P.R., and Olive, J.W.
2002. Recycled newspaper reduces nutrient leaching from container-grown poinsettia. HortScience 37(3): 516-519.
3 Huang, J.S., Nelson, P.V., Bailey,
D.A., Fonteno, W.C., and
Assessment of the need for nitrogen, phosphorus, potassium, and sulfur preplant nutrients for plug seedling growth. HortScience 37(3): 529-533.
4 Lighthiser, A.E., Nameth, S.G.P., and
problem for plantscape, yard, and garden? HortScience 37(3): 599.
5 Stapleton, J.J., Prather, T.S., Mallek, S.B., Ruiz, T.S. and Elmore, C.L. 2002. High
temperature solarization for production of weed-free container soils and potting mixes. HortTechnology 12(4): 697-704.