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JinSheng Huang and Paul V. Nelson

It is desirable to have a large root mass and compact shoot in the final stage of plug seedling production. Marigold `Discovery Orange' was grown for six weeks from sowing in a hydroponic system. Hoagland's all nitrate solution was used at 0.25X for the first three weeks and 0.5X for the final three weeks. P was applied continuously in the control and was eliminated for the first one or three weeks in the two stress treatments. Weekly mot and shoot dry weights indicated: a.) P stress caused an increase in root/shoot ratio with roots larger than in the control plants and b.) restoration of P after a P stress resulted in a rapid shift of root/shoot ratio back to the control level with final root and shoot weights less than in the control plants. A continuous marginal P stress or a stress near the end of seedling production is suggested. Tomato `Marglobe' was grown for five weeks and impatiens `Super Elfin White' for six weeks in a 3 sphagnum peat moss: 1 perlite substrate in 288 cell plug trays. Fertilizer was applied at every third watering at a zero leaching percentage. The control nutrient ratio (mM) was 5.4 NH4+ NO3: 0.5 PO4: 1.6 K while the low P treatments contained 0.15, 0.1, and 0.05 mM PO4 throughout the experiment. The root/shoot dry weight ratios increased in the low P treatments. Tomato plants at 0.15 and 0.1 mM P and impatiens plants at 0.15 mM P had larger roots than the control plants. A continuous stress at 0.15 mM PO4 appears promising.

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JiWeon Lee and Paul V. Nelson

Tomato `Marglobe' seed were sown on germination paper in enclosed plastic dishes in a growth room Ammonium was more toxic when applied as the single salt, ammonium sulfate, than when applied as part of a complete Hoagland solution. The lowest toxic ammonium levels were for the single salt 1.5 mM and for the complete solution 4.5 mM. Symptoms included reduced length of primary and particularly lateral roots, reduced numbers of root hairs, and chlorosis, distortion, and slower development of cotyledons. Tomato `Marglobe' seedlings were also grown in 288 cell plug trays in a substrate of 3 sphagnum peat moss and 1 perlite containing no N, P, or K but amended with dolomitic limestone to pH 6.0 They were fertilized every third watering with 4 mM NH4 + NO3, 0.4 mM PO4, and 1.2 mM K from 15 to 28 days after sowing and at double this concentration from 29 to 42 days. A zero leaching percentage was practiced. Ammoniacal-N comprised 25, 50, or 75% of total N. There were no effects of ammonium on root or shoot weights, height or appearance of plants through this period. Plant growth was limited throughout this period by N stress in accordance. with commercial practice. After 42 days N stress was alleviated by again doubling the nutrient solution concentration and applying it with every watering. Ammonium toxicity developed with symptoms of shorter plant height, general chlorosis of lower leaves, and necrosis of the base of lower leaves.

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Kimberly A. Williams and Paul V. Nelson

Soilless substrates have little capacity to sorb PO4. One way to reduce PO4 leaching during production is to increase the substrate retention of PO4. Adsorption isotherms were created at 25 C for alumina (aluminum oxide); the 2:1 calcined clays arcillite (montmorillonite plus illite) and attapulgite.; and a medium of 70 peat: 30 perlite using solutions of KH2PO4 at rates of P ranging from 0 to 20000 μg·ml-1. Material sorbed at the rate resulting in maximum P adsorption was then desorbed 22 times. Sorbing concentrations necessary to establish an equilibrium P concentration of 10 μg·ml-1 in the substrate solution were estimated from these curves. Materials were-charged with P at these estimated rates and evaluated in a greenhouse study in which each material was tested at 10 and 30% by volume of a 70 peat: 30 perlite substrate used to produce Dendranthema × grandiflorum `Sunny Mandalay'. Phosphate, K, and pH were determined on unaltered soil solutions biweekly throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. Isotherm and greenhouse data indicated that alumina, arcillite, and attapulgite effectively retained and slowly released K as well as PO4 over time. Alumina was most effective at retaining P, sorbing 16800 μg/cc compared to 3100 and 7800 μg P sorbed/cc for arcillite and attapulgite, respectively, when sorbed at P concentrations resulting in an equilibrium concentration of approximately 10 μg P/ml.

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Kimberly A. Williams and Paul V. Nelson

Soilless container medium components such as peatmoss and perlite have almost no capacity to retain PO4-P, and preplant amendments of triple superphosphate (TSP) are readily leached. Al amendments were tested to reduce P losses from these media. Al2(SO4)3 solutions at rates of 320 and 960 μg Al/cc were applied to a 70 peat: 30 perlite medium and dried at 70C. Adsorption isotherms were created at 25C for the Al2(SO4)3-amended media and an unamended control using solutions of Ca(H2PO4)2 at concentrations of P ranging from 0 to 500 μg·ml–1. Isotherms showed that P retention increased as Al concentration increased. In a greenhouse study, Dendranthema ×grandiflorum `Sunny Mandalay' was grown in these media with 100 g P/m3 from TSP incorporated into the mixes before planting. PO4-P, soluble Al, and pH were determined on unaltered medium solutions collected throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. The highest rate of Al was excessive and resulted in low pH and soluble Al levels in the medium solution early and in the cropping cycle, which were detrimental to plant growth. When Al was applied at 320 μg/cc, soluble Al levels in medium solution were not significantly higher than in the unamended control, PO4-P leached from TSP was reduced, and sufficient PO4-P was released throughout the cropping cycle to result in optimal plant growth.

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Janet F.M. Rippy and Paul V. Nelson

Variations in moss peat cation exchange capacity (CEC) and base saturation (BS) can result in inconsistent initial pH in moss peat-based substrates created using standard formulas for limestone additions and can lead to subsequent drift from the initial pH in those substrates. This study was conducted to determine the extent of such variation. CEC and BS were measured in three replications on 64 moss peat samples that were selected from three mires across Alberta, Canada, to represent maximum gradients in plant species composition within six degrees of decomposition acceptable for professional peat-based substrates. CEC ranged from 108 to 162 cmol·kg−1 (meq·100 g). Averaged overall samples, BS ranged from 15% to 71% of CEC and calcium accounted for 68%, magnesium for 25%, sodium for 5%, and potassium for 1.4% of BS. CEC was positively correlated to the amount of Sphagnum fuscum (Schimp.) Klingrr. in the sample (r = 0.22). BS was positively correlated to the amount of sedge (r = 0.28). Neither CEC nor BS was influenced by degree of decomposition (r = 0.002 and r = 0.08, respectively). Moss peats with high CEC have a greater buffering capacity than those with low CEC, resulting in less pH drift. Moss peats with high BS should have a low neutralization requirement to achieve a target pH. Understanding the species composition in peat-based substrates can alleviate problems of inconsistent initial pH and subsequent pH drift.

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Carl E. Niedziela Jr. and Paul V. Nelson

A new tube method for determining physical properties in container substrates was compared to an existing system. While both offer the advantages of undisturbed substrate and measurement of properties without altering the geometry of the substrate in the container, the tube method is easier to conduct. Both methods proved equally effective for determining air-tilled porosity, container capacity, total porosity, bulk density, and particle density.

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Kimberly A. Williams and Paul V. Nelson

A sustained release nutrient source suitable for maintaining steady, low (1 mM) N concentrations in the soil solution was sought as a component to be used in a system for reducing nutrients in the effluent of an open greenhouse cropping system. Several nutrient sources were evaluated as a N source incorporated singly in a medium of 1 sphagnum peat moss: 1 vermiculite and used to produce Chrysanthemum × morifolium `Sunny Mandalay'. All nutrients except N were applied additional to the sources tested. Sources tested included specific non-viable bacterial (B) and fungal (F) organisms from commercial biotechnological production lines, a microbial sludge mixture (S) from waste-water treatment, poultry waste-methane generator sludge (PS), mico-Osmocote (O), unsteamed bonemeal (BM), poultry feather meal (FM), and three-yeer aged pine needles (PM) at rates from 0.15 to 1.3 kg N·m-3. Based on periodic vacuum extracted soil solution analyses, leaf analyses, and plant growth, the efficacy of sources was in the order B, O> BM> S> PS> F, FM> PN. The 3 best sources provided sufficient N for 6 weeks; however, growth parameters did not differ from a complete liquid fertilization control until after 9 weeks. N in soil solution from the bacterial cells was at weeks 1, 3, 5, and 7: 142, 200, 73, and 3, mg·l-1, respectively.

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Kimberly A. Williams and Paul V. Nelson

Nutrient solution with a molar ratio of 10 N: 1 P: 3 K was applied in scheduled intervals at rates of 0.5, 1, 4, or 20 mm N (NO3 + NH4) to Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay' plants seven (7/day) or 14 times/day (14/day). These plants were compared to a 20 mm N control in which nutrient solution was applied when the soil moisture tension reached 30 kPa. Plants with 7/day had significant quadratic relationships for height, width, and dry weight, with the lowest responses at the low nutrient concentration. With 14/day, height and dry weight did not differ, although width did increase linearly with nutrient solution concentration. However, linear regression slopes for all three variables were much lower with 1Vday than with 7/day. At midcrop in both experiments, significant regression curves indicated that the lower concentrations of nutrient solution resulted in lower tissue N and K levels; however, slopes of the linear regressions were lower with 14/day than with 7/day. With 7/day, the water content (percentage) of plants in the schedule-fertilized treatments was higher in plants receiving higher nutrient concentrations, as indicated by the significant linear and quadratic regression curves. With 14/day, the water content was linearly related to solution nutrient concentration, but with a lower slope than with 7/day. These three trends indicate that steady-state nutrition was more closely achieved in a commercial-style substrate with 14/day applications of nutrient solution. These results suggest that plant growth that meets commercial expectations can be achieved at lower soil solution nutrient concentrations than currently applied.

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Tammy L. Everett and Paul V. Nelson

Five common sources of perlite used in the North American horticultural industry were tested for their release of fluoride during five successive teachings with pH 5.2 sodium phosphate buffer (1 cc perlite/ml buffer). Soluble fluoride in the first leachate ranged from 0.05 to 0.8 mg/l and in the fifth leachate from 0.01 to 0.18 mg/l. Lilium Asiatic hybrids `Pixie Grange' and `Sunray', Chlorophytum comosum (Thumb.) Jacques `Variegatum', and Gibasis pellucida (Martens & Gal.) D. Hunt `Bridal Veil' were. grown in sphagnum peat moss plus perlite substrates ranging up to 50% perlite and at substrate pH levels from 4.6 to 7.0. No fluoride toxicity occurred in these crops in any treatments. The precaution against the use of perlite in substrates used for growing fluoride sensitive crops needs to be reconsidered.

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Jin-Sheng Huang and Paul V. Nelson

Salinity guidelines for seed germination substrates are extremely low and difficult to attain given the salinity contributions of components such as peatmoss, vermiculite, limestone, wetting agent, and nutrients. This study was conducted to determine the value of N, P, K, and S as pre-plant nutrients with the anticipation that some could be eliminated. Seed were sown in two similar experiments on 23 Mar. and 6 June 1995 in 288-cell plug trays containing a substrate of 3 sphagnum peat: 1 perlite (v/v) amended with 6 g dolomitic limestone and 1.5 g Esmigran micronutrient mix per liter. Test plants included impatiens `Accent Rose' (Impatiens wallerana L.) and gomphrena `Buddy' (Gomphrena globosa. L.) Six preplant treatments including none, all, or all minus one of the nutrients N, P, K, and S were applied, each at a rate of 100 mg·L–1, substrate, in a randomized complete-block design with three blocks. Post-plant fertilization with 13–0.9–10.8 at 50 mg N/L began 1 week after sowing and was increased to 100 mg N/L when the fourth true leaf appeared. Omission of pre-plant K and S did not result in any reduction in final plant size in impatiens and only a minor reduction in one of the two gomphrena crops. Omission of N and P consistently reduced final size of plants by a commercially significant amount. While K and S are not necessary, N and P should be considered in a pre-plant fertilizer for these crops. In each situation where shoot size was smaller the root/shoot ratio was unchanged.