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Nitrate nitrogen is becoming a major pollutant in much of our nation's water supply. High levels of nitrate runoff are commonly found to occur from intense agricultural areas such as container nurseries. The objective of this study was to investigate combinations of liquid fertilizer (LF) plus controlled-release fertilizer (CRF) that would both minimize nitrate runoff and provide nutrient levels for optimum growth of Ilex verticillata L. The experiment was established in 1998 at the Iowa State Univ. Horticulture Research Station, Ames. Six fertilizer treatments were arranged in a randomized block design with eight replications. Treatment combinations of liquid fertilizer (LF) and controlled-release fertilizer (CRF) were [LF (mg/L)/CRF (g)]: 90/0, 90/8.5, 90/17, 180/0, 180/8.5, 180/17 (Peter's Excel 21-5-20 and Osmocote 18-6-12, 9-month release, respectively). Analysis of nitrate leaching showed that in 12 out of 16 weeks, the 180 mg/L LF treatments resulted in twice the amount of nitrate leached compared to the 90 mg/L LF. In 3 out of 16 weeks, treatments containing 0 g CRF leached significantly less nitrate than those containing 17 g CRF. None of the treatments produced a difference in total dry weight or caliper of Ilex verticlillata L. This data suggests that plant growth remains similar over a range of fertilizer input and higher rates of applied LF result in higher nitrate leaching.
Iowa State Univ. is committed to improve student learning and supports faculty and staff through Project LEA/RN (Learning Enhancement Action/Resource Network) workshops and continuous training. Project LEA/RN teaches cooperative learning techniques that are known to improve student interest in the subject, allow active participation, improve understanding and retention of the material, and encourage learning inside and outside the classroom. Three learning techniques that have been used successfully in our lecture and laboratory classes ranging from 20 to 100 students per class are: turn to your partner (TTYP), note-taking pairs (NTP), and jigsaw. In TTYP, the instructor asks a question and students formulate an answer individually, then share the answer with a partner, listen to the partner's answer, and finally create a new answer through discussion. NTP can be used after new material has been presented. A student compares notes with their partner, both add/correct their notes, share key points with a partner, and carefully listen to the partner's keypoints. In the jigsaw exercise, students who had the same assignment compare information they have prepared with each other and then with the entire class. In all exercises students are made accountable by the instructor who calls randomly on individuals to share their answers with the class. Examples of how to use these techniques and the interpersonal skills acquired and practiced during these exercises will be discussed.
A rapid screening system was developed to identify plant-beneficial rhizobacteria useful in protecting nursery seedlings against damping-off caused by Rhizoctonia solani. Ornamental and agricultural crops were planted into 100 soil samples that were collected from various fields throughout California. More than 7000 bacterial strains from the rhizosphere of these crops were isolated and tested in vitro for antibiosis against R. solani AG4. In a second tier, 600 active strains were tested in planting trays seeded with radish (Raphanus sativus `Cherry Belle'). Each planting cell filled with commercial potting mix contained millet-grown R. solani inoculum in the center and eight radish seeds at the periphery. Bacteria were cultured for 24 hr at 25°C in 10% tryptic soy broth and were applied as a drench at 1 × 107 cfu/cc to each cell. Trays were incubated in a growth chamber at 21°C and a 10-hr photoperiod. Post-emergence damping-off occurred within 8 to 9 days after planting, and no further losses were observed after 14 days. Approximately 0.5% of the original 7000 bacterial strains tested reduced damping-off significantly. Fifteen bacterial strains controlled Rhizoctonia damping-off by 30% to 60% compared to the non-treated control.
Twelve species of woody ornamental plants were grown for 2 years in containers at Riverside and Davis, Calif., to determine plant water use (WU) and compare crop coefficients (Kcs). WU was determined gravimetrically in 1993 and 1994, five times each year in Riverside and four times each year in Davis. WU and Kc were affected by significant interactions among species, location, and time of year. WU was primarily influenced by the month, while Kc was most affected by location. Rhaphiolepis and Pittosporum, followed by Juniperus and Photinia, respectively, were the highest water users in Riverside when averaged over the 2 years. Arctostaphylos was the highest water user in Davis, followed by Juniperus, Cercis, and Pittosporum, respectively. Rhamnus, Prunus, and Cercocarpus were among the lowest water users in both locations. Heteromeles, Buxus, and Ceanothus were intermediate water users. The largest difference in species WU between the two locations was found for Arctostaphylos and Cercis, both high water users in Davis, but moderate or low water users in Riverside. The other species ranked similarly in both locations. Kcs of the 12 species, when averaged over the 2-year sampling period, ranked similar to water use. Kcs tended to be artificially high in the winter months and were not correlated to the low WU during that time.
Water stress and N fertilization can have a profound effect on populations of phytophagous insects. While species and cultivar selection can identify plants that are resistant to common insect pests, cultural practices may further decrease the susceptibility to insect attacks. Six poinsettia and six chrysanthemum cultivars were grown under well-watered or water-deficient conditions, and three fertilizer regimes with low, medium, or high concentrations of N. Vegetative plant growth and longevity and fecundity of various insect pests on these plants were determined. Host plant suitability to insects was estimated by the quantity of foliar soluble protein. Low irrigation reduced leaf area and leaf and stem dry weights 36% to 41% in poinsettias and 26% to 28% in chrysanthemum. Leaf area and leaf dry weight increased linearly in response to increasing fertilizer concentrations in poinsettia and chrysanthemum. Cultivar-specific differences were found for all variables of vegetative growth in poinsettiasand chrysanthemum. Cultivar also strongly affected insect preference, development, and fecundity. Low irrigation significantly reduced insect survivorship of the silverleaf whitefly on poinsettias. On chrysanthemum, leafminers, thrips, and melon aphids were unaffected by irrigation or fertilizer treatments. Chrysanthemum cultivar choice strongly affected the number of insects or development time.
Water stress and N fertilization can have a profound effect on populations of phytophagous insects. While species and cultivar selection can identify plants that are resistant to common insect pests, cultural practices may further decrease the susceptibility to insect attacks. Six poinsettia and six chrysanthemum cultivars were grown under well-watered or water-deficient conditions, and three fertilizer regimes with low, medium, or high concentrations of N. Vegetative plant growth and longevity and fecundity of various insect pests on these plants were determined. Host plant suitability to insects was estimated by the quantity of foliar soluble protein. Low irrigation reduced leaf area and leaf and stem dry weights 36% to 41% in poinsettias and 26% to 28% in chrysanthemum. Leaf area and leaf dry weight increased linearly in response to increasing fertilizer concentrations in poinsettia and chrysanthemum. Cultivar-specific differences were found for all variables of vegetative growth in poinsettiasand chrysanthemum. Cultivar also strongly affected insect preference, development, and fecundity. Low irrigation significantly reduced insect survivorship of the silverleaf whitefly on poinsettias. On chrysanthemum, leafminers, thrips, and melon aphids were unaffected by irrigation or fertilizer treatments. Chrysanthemum cultivar choice strongly affected the number of insects or development time.