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Stuart L. Warren and Ted E. Bilderback

Irrigation of container-grown ornamental crops can be very inefficient, using large quantities of water. Much research was conducted in the 1990s to increase water efficiency. This article examined water management, focusing on three areas: water application efficiency (WAE), irrigation scheduling, and substrate amendment. Increases in WAE can be made by focusing on time-averaged application rate and pre-irrigation substrate moisture deficit. Irrigation scheduling is defined as the process of determining how much to apply (irrigation volume) and timing (when to apply). Irrigation volume should be based on the amount of water lost since the last irrigation. Irrigation volume is often expressed in terms of leaching fraction (LF = water leached ÷ water applied). A zero leaching fraction may be possible when using recommended rates of controlled-release fertilizers. With container-grown plant material, irrigation timing refers to what time of day the water is applied, because most container-grown plants require daily irrigation once the root system exploits the substrate volume. Irrigating during the afternoon, in contrast to a predawn application, may increase growth by reducing heat load and minimizing water stress in the later part of the day. Data suggest that both irrigation volume and time of application should be considered when developing a water management plan for container-grown plants. Amending soilless substrates to increase water buffering and reduce irrigation volume has often been discussed. Recent evidence suggests that amending pine bark substrates with clay may reduce irrigation volume required for plant production. Continued research focus on production efficiency needs to be maintained in the 21st century.

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Helen T. Kraus and Stuart L. Warren

Five ratios of NH4:NO3 (100:0, 75:25, 50:50, 25:75, and 0:100) were evaluated for impacts on growth of Cotoneaster dammeri Schneid. `Skogholm' (cotoneaster) and Rudbeckia fulgida Ait. `Goldsturm' (rudbeckia). Nitrate decreased dry weight and leaf area, while nutrient solutions containing >25% NH4 increased shoot and root growth of cotoneaster and rudbeckia. Additionally, NO3 decreased accumulation of some cationic nutrients and N in roots and shoots of cotoneaster and rudbeckia compared to solutions containing either NH4 alone or mixes of NH4 and NO3. Nitrogen contents (in milligrams) in cotoneaster fertilized with NO3 decreased an average of 54% and 58% in rudbeckia compared to N supplied as NH4 alone. These dramatic reductions in growth and tissue nutrient content reiterate the need for proper N form selection. Root diameter of cotoneaster was higher with a mix of NH4 and NO3 than with NO3 alone; whereas, the N form had no impact on diameter of rudbeckia roots. However, the stele of both cotoneaster and rudbeckia roots was larger and contained more secondary xylem with larger tracheary elements with a mix of NH4 and NO3 compared to nutrient solutions with NO3 alone. Increased number and size of secondary tracheary elements may relate to increased dry weight and leaf area of both cotoneaster and rudbeckia fertilized with mixes of NH4 and NO3 compared to NO3 alone.

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Helen H. Tyler and Stuart L. Warren

An experiment with a factorial treatment combination in a split plot design with five single plant replications was conducted to evaluate the effects of five rates of fertilizer addition and two irrigation volumes on plant growth in a composted turkey-litter-amended pine bark substrate. Main plots were daily applications of 600 or 900 ml/3.8-L container. Subplots were either 0, 1.0, 2.0, 3.0, or 4.0 g N additions (Osmocote High H 24N–1.7P–5.8K) per container topdressed on a substrate composed of pine bark amended with 8% (by volume) composted turkey litter. No additional amendments were made to the compost amended substrates. An additional “industry control” treatment consisted of an 8 pine bark: 1 sand (by volume) substrate amended with 3.0 kg/m3 dolomitic limestone and 0.9 kg/m3 Micromax and topdressed with 3.5 g N (Osmocote High N) per container. After 134 days, Cotoneaster dammeri `Skogholm' and Rudbeckia fulgida `Goldsturm' plants were harvested and shoot and root (cotoneaster only) dry weights were determined. Cotoneaster shoot and root dry weights and rudbeckia shoot dry weight increased linearly as N rate increased from 0 to 4.0 g N. Irrigation volume did not affect cotoneaster shoot or root dry weights. Rudbeckia shoot dry weight was 18% greater with 900 ml than with 600 ml of irrigation. Rudbeckia growth in compost amended substrate was greater than in the industry control when topdressed with ≥1.0 g N. Shoot growth of cotoneaster in the industry control substrate and compost amended substrate with ≥ 3.0 g N applied was similar.

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Helen T. Kraus and Stuart L. Warren

An experiment was conducted to develop a protocol for using compost in nursery crop production. Five rates of inorganic fertilizer (0, 1, 2, 3, and 4 g N) and two irrigation volumes (600 and 900 mL per 3.8-L container) were evaluated for their effects on Rudbeckia fulgida Ait. `Goldsturm' and Cotoneaster dammeri Schneid. `Skogholm' growth in a pine bark substrate amended with composted turkey litter (CTL). Additions of ≥2 g N per container for cotoneaster and ≥1.0 g N for rudbeckia were required to produce growth equivalent to that of plants in a control treatment that simulated typical production by a grower in the southeastern United States. Phosphorus, Ca, and Mg contents of cotoneaster and rudbeckia plants grown in CTL-amended substrates with no fertilizer added (0 g N) were similar to or greater than that of the control. Phosphorus concentrations in the substrate solutions were higher in all CTL-amended substrates than in the control regardless of fertilizer addition. This suggests that P released from CTL had a greater impact than P added with fertilizer. The greatest nutrient value of CTL may be as a P source and a replacement for dolomitic limestone and micronutrients in container-grown plant production.

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L. Eric Hinesley, Stuart L. Warren and Layne K. Snelling

In two experiments, uniconazole (0.25 to 16 mg·L-1 a.i.) was applied as a root drench to containerized Fraser fir [Abies fraseri (Pursh) Poir.] at various times of the year. Leader length, stem diameter, length of laterals, and number of subterminal buds were reduced the following growing season. Treatment during the 1994 growing season reduced lateral bud formation on the leader in 1995, whereas treatment with 8 or 16 mg·L-1 in Mar. 1995 (prior to budbreak) increased it. Uniconazole caused needle discoloration and abscission at concentrations ≥4 mg·L-1. Leader growth was reduced more than branch elongation, which tended to make plants more decurrent. The utility of uniconazole in production of tabletop Fraser fir Christmas trees was unclear; reduced shoot elongation was often accompanied by fewer lateral buds and needle discoloration and/or abscission. Chemical name used: E-1-(p-Chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazole-1-penten-3-ol) (uniconazole).

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Helen T. Kraus, Robert L. Mikkelsen and Stuart L. Warren

Traditional N mineralization studies have been conducted by soil scientists using soils and temperatures found in field production. As temperature, in part, governs the rate of mineralization, and container substrates reach much higher temperatures than do soils, the effect of these elevated temperatures on mineralization must be considered to begin to understand N mineralization in container substrates during production. The N mineralization patterns of three composts [turkey (Meleagris gallopavo) litter, yard waste, and municipal waste] were determined under three temperature regimes (45, 25, and 45/25 °C). More organic N was mineralized from composted turkey litter (CTL) than from municipal or yard composts, regardless of temperature. The percentage of organic N mineralized from CTL was greater at 45/25 and 45 °C than at 25 °C.

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Helen H. Taylor, Robert L. Mikkelsen and Stuart L. Warren

The N release patterns of composted turkey litter, composted yard waste, and composted municipal waste amended pine bark substrates were measured under simulated diurnal temperature variations [25C, 45C, and 45/25C (14/10 h)] found in container substrates. Temperature regime, compost, and the interaction between temperature and compost affected the NH4 and NO3 availability and the total N released from the composted waste products over the 16-week experiment. Within each temperature regime, the composted turkey litter released greater amounts of NH4 and more total inorganic N than the municipal and yard wastes. The turkey litter yielded the highest NO3 concentrations at 25C, while the municipal waste produced the highest NO3 concentrations at the 45C and the 45/25C temperatures. Temperatures higher than 25C inhibited nitrification in the turkey litter-amended substrates; however, the 45C and the 45/25C treatments resulted in greater total N mineralization than the 25C treatment.

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Stuart L. Warren, C. Ray Campbell and Walter A. Skroch

Fraser fir [Abies fraseri (Pursh) Poir.] and Norway spruce [Picea abies (L.) Karst.] were grown in seven vegetation management programs ranging from 100% cover of grass-dominated vegetation to bare soil on opposing north and south aspects. Concentrations of 13 nutrients were determined at three growth stages during 2 years: active terminal growth, cessation of terminal expansion, and dormancy. Aspect did not affect nutrient concentrations. Vegetation management programs bad a significant impact on nutrient concentration for both species. Nitrogen, Ca, B, Fe, and Mn concentrations during dormancy were negatively correlated with herbaceous biomass. In contrast, N during active growth and P and Mg concentrations during all stages were positively correlated with herbaceous biomass. Vegetation management only affected the seasonal trend of Mo. Seasonal trends varied by nutrient in both species.