Tissue concentrations of Ca, Mg, and K were determined across immature leaves of lettuce (Lactuca sativa L. `Buttercrunch') at different stages of enlargement using electron microprobe x-ray analysis. The analysis was with a wavelength dispersive spectrometer to permit detection of low concentrations of Ca. Patterns of mineral accumulation in immature leaves that were exposed were compared to patterns of accumulation in leaves that were enclosed within a developing head. The leaves developing without enclosure were free to transpire and developed normally whereas leaves developing with enclosure were restricted in transpiration and developed an injury that was characteristic of Ca deficiency. In the exposed leaves, Ca concentrations increased from an average of 1.0 to 2.1 mg·g-1 dry weight (DW) as the leaves enlarged from 5 to 30 mm in length. In the enclosed leaves, Ca concentrations decreased from 1.0 to 0.7 mg·g-1 DW as the leaves enlarged from 5 to 30 mm in length. At the tips of these enclosed leaves a larger decrease was found, from 0.9 to 0.3 mg·g-1 DW during enlargement. Necrotic injury first became apparent in this tip area when the concentration was ≈0.4 mg·g-1 DW. Magnesium concentrations across the exposed leaves were similar to concentrations across the enclosed leaves, and did not change with enlargement. Magnesium concentrations averaged 3.5. mg·g-1 DW in both enclosed and exposed leaves during enlargement from 5 to 30 mm. In both exposed and enclosed leaves, K concentrations increased during enlargement from 40 to ≈60 mg·g-1 DW. Potassium concentrations were highest toward the leaf apex and upper margin where injury symptoms occurred, and this may have enhanced injury development. This research documents the critical low levels of Ca (0.2 to 0.4 mg·g-1 DW) that can occur in enclosed leaves of plants and which apparently leads to the marginal apex necrosis of developing leaves seen frequently on lettuce and other crops.
Daniel J. Barta and Theodore W. Tibbitts
Daniel J. Barta and Theodore W. Tibbitts
An electron microprobe was used to determine tissue concentrations of Ca across 20-mm-long leaves of `Green Lakes' crisphead lettuce (Luctuca sativa L.) with and without tipburn injury. Concentrations within the fifth and 14th leaves, counted from the cotyledons, from plants grown under controlled-environment conditions were compared to concentrations within similar leaves obtained from plants grown under field conditions. Only the 14th leaf from plants grown under controlled-environment conditions developed tipburn. Injured areas on these leaves had Ca concentrations as low as 0.2 to 0.3 mg·g-1 dry weight. Uninjured areas of tipburned leaves contained from 0.4 to 0.5 mg·g-1 dry weight. Concentrations across the uninjured 14th leaf from field-grown plants averaged 1.0 mg·g-1 dry weight. Amounts across the uninjured fifth leaves from both environments averaged 1.6 mg·g-1 dry weight. In contrast, Mg concentrations were higher in injured leaves than in uninjured leaves and thus were negatively correlated with Ca concentrations. Magnesium concentrations averaged 4.7 mg·g-1 dry weight in injured leaves compared with 3.4 mg·g-1 dry weight in uninjured leaves from both environments. Magnesium concentrations were uniform across the leaf. Potassium concentrations were highest at the leaf apex and decreased toward the base and also decreased from the midrib to the margin. Potassium averaged 51 mg·g-1 dry weight in injured and uninjured leaves from both environments. No significant differences in K concentration were present between injured and uninjured leaves. This study documented that deficient concentrations of Ca were present in areas of leaf tissue developing tipburn symptoms and that concentrations were significantly higher in similar areas of other leaves that had no symptoms. This study also documented that Ca concentrations were significantly lower in enclosed leaves that exhibited tipburn symptoms than in exposed leaves that did not exhibit tipburn. Also, the amounts of Ca in plants that developed tipburn in controlled environments were lower than in plants of the same cultivar that did not develop tipburn in field plantings. The reduced levels of Ca in plants grown in controlled environments were associated with faster development rates compared with field-grown plants.
Jan-W. Briedé, James T. Fisher and Daniel J. Manuchia
The gas exchange of tomato (Lycopersicon esculentum Mill cv. Spring Giant VF) plants exposed to an ethephon root drench of 5 μl·liter-1 or 50 μl·liter-1 was examined for 9 days. Photosynthesis showed a biphasic response to ethephon, wherein elevations of 13.2% and 16.7% were observed over control plants for two of the measurement days for the 50 and 5 μl ethephon/liter concentrations, respectively. Stomatal conductance showed a large increase at 50 μl ethephon/liter on day 2, while 5 μl·liter -1 did not show this difference. A biphasic response of photosynthesis may explain some of the intraspecific variation found in the literature describing ethylene-induced gas-exchange alterations.
Ray E. Worley, J.W. Daniel, J.D. Dutcher and K.A. Harrison
Nitrogen at rates of 112 or 224 kg·ha-1 was applied to nonirrigated and drip irrigated mature pecan trees for 9 years. Some irrigated trees received 224 kg·ha-1 N either all broadcast or ½ through the drip irrigation. Other drip irrigated trees received only 112 kg·ha-1 all through the drip irrigation system. Fertigation was in 4 equal monthly doses beginning April 1. Irrigation increased yield for 2 years for Schley and 3 years for Stuart. Nut size was increased by irrigation in 6 years for Schley and 8 years for Stuart. Applying ½ N through the irrigation system caused no detrimental effect on yield or nut quality. The lower rate of N all applied through the drip irrigation system gave yield and nut quality as good as the higher rate either all broadcast or ½ broadcast and ½ fertigated.
R.E. Worley, J.W. Daniel, J.D. Dutcher, K.A. Harrison and B.G. Mullinix
No reduction in yield and quality of pecan nuts or leaf mineral nutrient concentration occurred when 100 lb/acre of N was applied through a drip-irrigation system compared with 200 lb/acre applied either all broadcast or half broadcast and half fertigated. Yield of `Stuart', percentage kernel of `Schley', and nut size of both cultivars were increased by irrigation or irrigation and fertigation. The 100 lb/acre N-all-fertigated treatment resulted in less soil pH reduction and less loss of K, Ca, and Mg from soil underneath the tree canopy than broadcast treatments. No evidence of excessive soil pH reduction in the wetted zone of fertigated trees was noticed. Calcium and Mg were higher within than outside the wetted zone.
Jeffrey S. Karns, Cathleen J. Hapeman, Walter W. Mulbry, Elmer H. Ahrens and Daniel R. Shelton
Daniel I. Leskovar, J. Clark Ward, Russell W. Sprague and Avraham Meiri
Restrictions on pumping water from underground aquifers are limiting vegetable production in Southwest Texas. To determine yield, quality, and water use efficiency (WUE) of muskmelon (Cucumis melo L. group Cantalupensis, `Caravelle'), six irrigation systems with varying input levels and their interactions with stand establishment (containerized transplants vs. direct seeding) were examined. Irrigation systems were: 1) pre-irrigated followed by dryland conditions; 2) furrow/no mulch; 3) furrow/mulch (40-μm-thick black polyethylene); 4) surface drip (0 cm depth)/mulch; 5) subsurface drip (10-cm depth)/mulch; and 6) subsurface drip (30-cm depth)/mulch. Field experiments were conducted on a silty clay loam soil during four seasons (1995-98). In 1995, marketable fruit yields were greater for subsurface drip systems at 30-cm depth than for furrow systems, with or without plastic mulch. Transplants grown with surface drip irrigation produced 75% greater yield in the 9-count fruit class size during early harvest than did those grown with subsurface drip (10- or 30-cm depth), but total yield was unaffected by drip tape depth placement. In 1996, the driest season of these studies, direct-seeded plants had higher total yields than did transplants; yield was greatest for direct-seeded plants on subsurface drip placed at 10- or 30-cm soil depth, and for transplants on subsurface drip at 10-cm depth. Soluble solids content was minimally affected by irrigation method, but was higher in fruit from transplants than in those from direct-seeded plants in 3 years. Across all seasons, the average water applied for drip systems was 53% lower than that for conventional furrow systems, and WUE was 2.3-fold as great.
Michael A. Arnold, R. Daniel Lineberger, Tim D. Davis, David W. Reed and William J. McKinley
A comprehensive survey of American and Canadian universities that offer masters, doctoral, or both degrees in horticulture resulted in responses from 27 academic units. Units were surveyed regarding types of degrees offered, admissions policies, demographic characteristics of students, financial assistance provided to students, faculty ranks and salaries, and metrics by which the programs were evaluated by university administration. About 80% of the programs resided in 1862 Morrill Act land-grant institutions (LG) with the remainder housed in other non-land-grant institutions (NLG). Thirty-eight percent of reporting LG programs existed as stand-alone horticulture departments, whereas horticulture programs were combined with other disciplines in the remainder. Admissions criteria were most consistent among LG programs. Participation in distance education programs was low, but growing. Financial support of graduate students was more common in LG programs. Most schools offered some sort of tuition reduction to those students on assistantships/fellowships and offered health insurance options. Payment of fees was rare and the level of stipends provided varied substantially among programs. International student enrollment was greatest at LG programs and had remained steady in recent years. Gender equity was present among graduate students, with nearly equal male and female enrollment. Most graduate students at both LG (63.6%) and NLG (75.0%) programs were non-Hispanic White; although overall minority enrollment had increased but was still not similar in distribution to that of the general U.S. population. Professors (46.7%) and Associate Professors (28.3%) dominated the faculty ranks while Assistant Professors (19.3%) and lecturers/instructors (5.7%) constituted a much smaller portion of the faculty. Faculty salaries varied tremendously among institutions, especially for senior faculty. Female and ethnic minorities were underrepresented in faculty ranks compared with the general U.S. population. Aside from total graduate program enrollment, the relative importance of various evaluation metrics for programs was highly variable among institutions. Data discussed herein should be useful to universities with horticulture graduate programs for peer institution comparisons during program assessments, accreditation reviews, or for strategic planning purposes.
James P. Gilreath, Timothy N. Motis, Bielinski M. Santos, Joseph W. Noling, Salvadore J. Locascio and Daniel O. Chellemi
Field studies were conducted during four consecutive tomato (Lycopersicon esculentum) -cucumber (Cucumis sativus) rotations to examine the longterm residual effects of tomato methyl bromide (MBr) alternatives on soilborne pests in double-cropped cucumber. Four treatments were established in tomato fields: a) nontreated control; b) MBr + chloropicrin (Pic) (67:33 by weight) at a rate of 350 lb/acre; c) tank-mixed pebulate + napropamide at 4 and 2 lb/acre, respectively, followed by 1,3-dichloropropene (1,3-D) + Pic (83:17 by volume) at 40 gal/acre; and d) napropamide at 2 lb/acre followed by soil solarization for 7 to 8 weeks. Each of the following seasons, cucumber was planted in the same tomato plots without removing mulch films. For nutsedge [purple nutsedge (Cyperus rotundus) and yellow nutsedge (C. esculentus)] densities, napropamide followed by solarization plots had equal control (≤15 plants/m2) as MBr + Pic during all four cropping seasons. However, nematode control with solarization was inconsistent. Marketable yield data proved that fumigation in tomato fields with either MBr + Pic or pebulate + napropamide followed by 1,3-D + Pic had a long-term effect on double-cropped cucumber.
Etaferahu Takele, John A. Menge, John E. Pehrson Jr., Jewell L. Meyer, Charles W. Coggins Jr., Mary Lu Arpaia, J. Daniel Hare, Darwin R. Atkin and Carol Adams
The effect of various integrated crop management practices on productivity (fruit yield, grade, and sire) and returns of `Washington Navel' oranges [Citrus sinensis (L.) Osbeck] was determined in the San Joaquin Valley of California. Seventy-two combinations of treatments comprised of three irrigation levels [80%, 100%, and 120% evapotranspiration demand (ETc)], three N fertilizer levels (low, medium, and high based on 2.3%, 2.5%, and 2.7% leaf N, respectively), gibberellic acid (±), miticide (±), and fungicide-nematicide (±) were included in the analysis. Using a partial budgeting procedure, returns after costs were calculated for each treatment combiition. Costs of treatments, harvesting, packing, and processing were subtracted from the value of the crop. The value of the crop was calculated as the sum of returns of crop in each size and grade category. The overall result indicated that returns after costs were higher for the +fungicide-nematicide treatment and also were generally more with increased irrigation. The combination of 120% ETc, +fungicide-nematicide, medium or high N, -miticide, and -gibberellin showed the highest return of all treatment combinations. Second highest returns were obtained with high N or with miticide and gibberellin used together.