During the past decade virtually all undergraduate programs in the agricultural sciences in the U.S. have been revised. The revisions were caused by many factors, including large increases in student numbers, changes in the background of students (e.g., rural vs. urban), environmental concerns and changing agricultural technology. The purpose of this article is to suggest the need for further revision to broaden the curriculum and its students in order to meet the challenges they will face in the years ahead.
A phase change material (PCM) energy storage unit operating in a greenhouse from 29 Oct. through 21 Dec. 1992 cooled it on the average 1.7C in the day and warmed it 2.2C at night due to both sensible and latent heat absorbed, released, and circulated. Tagetes patula `Mighty Marietta' and `Early Queen Sophia' marigolds and Viola × Wittrockiana `Yellow Blotch' and `Blue Blotch' pansies were grown in a PCM and a control (no PCM) greenhouse. Temperatures went below 0C 10 days in the control greenhouse and 4 days in the PCM greenhouse. The lowest temperature of -7.8C killed the marigolds in the control greenhouse. Neither marigolds nor pansies were killed in the PCM greenhouse, which attained a low temperature of -3.3C. On 4 Dec., plants were destructively harvested. Morphologically the marigolds were taller, and had more leaf area and dry matter when grown in the PCM greenhouse as compared to the control, but pansies were taller, and had more leaf area and dry matter when grown in the control greenhouse, as compared to the PCM greenhouse.
Geranium seedlings (Pelargonium × hortorum L.H. Bailey ‘Mustang’) were greenhouse-grown at a plant density (PD) of 85, 170, 255, or 340 plants/m2 for two time periods (21 to 34 days and 35 to 62 days from sowing). There was a positive linear regression between PD and crop productivity (CP), expressed as g dry matter/day per m2; between PD and crop productivity efficiency (CPE), expressed as percent of energy in the photosynthetic photon flux (PPF) incident on the crop that is stored in crop dry matter as energy of combustion; and between PD and leaf area index (LAI) for both time periods. Plant top dry weight, leaf area, length of longest petiole, and main stem length and height were not affected by PD at 35 days from sowing. However, at 63 days from sowing there was a negative linear regression between PD and both plant top dry weight and main stem length, and a positive linear regression between PD and both plant height and length of the longest petiole.
Static solution culture systems are widely used in plant research and for teaching demonstrations of plant nutrient deficiency symptoms. Numerous systems have been described (1,2) including one (3) constructed of readily available materials. Reported here is another design for a static solution culture system built of readily available components. This system is characterized by a) low cost, b) simplicity, c) easy assembly, d) potential for variable spacing of culture vessels, e) identical aeration rate for each vessel without individual air flow valves, and f) aeration from the top of the culture vessel rather than the bottom, eliminating drainage through aeration lines should the air supply fail.
Calcium deficiency symptoms of heartleaf philodendron (Philodendron scandens ssp. oxycardium) were reported to occur first on the vine's basal leaves, with the tip or uppermost leaves the last to develop symptoms (1). This pattern of symptom development was interpreted to indicate that philodendron was an exception to the generalization that Ca is immobile in plants, i.e., in philodendron, Ca was translocated from basal to upper leaves (5). Since Ca deficiency symptoms occur in meristematic areas (such as shoot and root tips), Ca is considered immobile in plants (2). Thus, the report of Ca deficiency symptoms on basal leaves of philodendron (1) was indeed exceptional. Unfortunately, there was no report of the recovery of the deficient plants when fertilized with Ca, nor any Ca analysis of philodendron tissue, to confirm that Ca deficiency was the cause of the observed symptoms (1) and to support the conclusion that Ca was mobile (5). The purpose of this study was to produce Ca deficiency symptoms in heartleaf philodendron to determine if Ca deficiency symptoms occur on basal leaves, as originally reported (1).
Seedlings of Begonia × semperflorens-cultorum Hort. ‘Scarletta’ were grown in a greenhouse at a plant density of 193 plants/m2. Crop productivity (grams of dry matter produced per day per square meter of crop) and crop productivity efficiency (percentage of the photosynthetic photon flux incident on the crop that is stored in the form of crop dry matter as energy of combustion) did not increase when the photoperiod was extended from 9 to 13 hr with incandescent lights. However, stem and petiole length did increase under 13- compared to 9-hr photoperiods. Crop productivity of begonia was less than maximum values reported for some other bedding plants. However, when crop growth was expressed in terms of fresh weight rather than dry weight, begonia crop growth exceeded that reported for other bedding plants. This increased growth seemed to be due to the low dry weight to fresh weight ratio in wax begonia of 0.03.
Crop productivity efficiencies (CPE) of around 8% (the ratio of the dry weight gain of the crop to the potential to produce dry weight), were realized with petunias (Petunia hybrida Villm.), provided that the crop canopy was essentially closed at the beginning of the 9- to 12-day experimental periods and that there were many branches (sinks). This was found at either long or short photoperiods or at either a normal (15.6°C) or reduced (7.2°) temperature for the 16-hour night periods. Long photoperiods resulted in significantly increased CPE through increased size of the leaves before the crop canopy was closed. Elevated root temperature increased CPE after a sizeable number of lateral branches had formed.
Geranium seedlings (Pelargonium × hortorum L.H. Bailey, ‘Mustang’) grown in 13 hr photoperiods were 23% taller due to stem and petiole elongation, had larger leaves, and prior to canopy closure had a higher crop productivity efficiency (CPE) than seedlings grown under 9 hr photoperiods. In general, the tallest plants were produced when grown with soil temperatures of 18°C. The highest weekly CPE attained was 3.8%.
Seedlings of Petunia hybrida ‘Snow Cloud’ and Pelargonium × hortorum ‘Red Elite’ and ‘Cardinal Orbit’ were grown to anthesis at day air temperatures of 27° ± 3°C (9 hr) and either 7° ± 3° or 18° ± 3° night air temperatures (15 hr). Petunia crop productivity (CP, grams of dry matter produced per square meter of crop) and crop productivity efficiency (CPE, percentage of photosynthetic photon flux incident on the crop stored in the form of crop dry matter) were the same at both temperature regimes from canopy closure to anthesis, but anthesis was delayed 10 days at 7°. Petunias grown at 7° had four more basal branches and were only one-third the height of petunias grown at 18° (12 vs. 37 cm). CP and CPE were 20% lower for geraniums grown at 7° compared to CP and CPE for geraniums grown at 18°. The geraniums grown at 7° flowered 3 weeks later, were more compact, and were 16 to 19 cm shorter than geraniums grown at 18°.
Seedlings of Petunia hybrida cv. Snow Cloud were subjected to root zone temperatures at the bottom surface of the pots of 15.6° to 19.4°C (NT) or 21° to 35° (HT) and photoperiods of 9 (SD) or 13 hr (LD) for 25 days in a eontrolled-environment chamber with air temperatures of 21° for 9 hr and 15.6° for 15 hr. HT × LD plants produced the largest total leaf area, largest main stem leaves, and most dry weight of all treatments; they were tallest and bloomed first, but had the fewest lateral branches. HT × SD plants developed the most lateral branches at the fastest rate and had a total leaf area, dry weight gain, and root development comparable to those of the LD treatments. NT × SD plants were the smallest. Crop productivity efficiency was determined to be NT × SD = 2.9%, HT × SD = 3.4%, NT × LD = 3.7%, and HT × LD = 3.9%.