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  • Author or Editor: V.M. Russo x
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Senescence occurs at the cellular and tissue levels. It is under genetic and environmental control and factors affecting initiation and speed of development of senescence can be passed from parental to F1 plants. This study was conducted in the greenhouse and field to determine how senescence patterns in F1 plants of a shrunken2 sweet corn (Zea mays L.) hybrid compared to those of parental inbreds. Greenhouse grown plants were left intact and field grown hybrids and parental inbreds had one or both reproductive organs removed or were left intact. Senescence patterns in stalk internodes were similar in greenhouse and field grown F1 and inbred plants. Senescence patterns in shank internodes in greenhouse grown plants were different from those of field grown plants. Senescence ratings in stalks increased as developmental stage advanced. Expression of stalk senescence in internodes below the node bearing ears appears to be suppressed by hybrid vigor. In field tests, destruction of the tassel before expansion (decapitation) appears to suppress senescence in internodes above I7, with this effect somewhat dependent on plant developmental stage.

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The effects of soil depth on yields of dry bean (Phaseolus vulgaris) produced under different types of tillage is not well understood. Black and pinto bean yields were evaluated under conventional and reduced-tillage for 2 years in a 3.24-ha (8-acre) commercial field in southeastern Oklahoma. Before planting, a grid pattern was laid out on the field with points at every 13.7 m (45.0 ft) north to south and 6.1 m (20.0 ft) east to west. Samples were taken at each intersection of the grid lines (496 sites) to determine pH, and the amounts of nitrogen, phosphorus, and potassium present in soil. Depth to an impervious clay pan was determined at these sites, and were grouped as being one of the following: <25 cm (9.8 inches), >25 to 50 cm (19.7 inches), >50 to 75 cm (29.5 inches) and >75 cm. Irrigation was supplied, if needed, at 50% flowering and, in both years, at 50% pod set. There was no significant effect on yield due to year. Black bean yields from conventional tillage averaged 1166 kg·ha-1 (1040.4 lb/acre) across soil depths and were better than yields from reduced-tillage which averaged 136 kg·ha-1 (121.3 lb/acre). Pinto bean yields from conventional tillage were 611 kg·ha-1 (545.2 lb/acre) across soil depths and were better than for reduced tillage, which averaged 403 kg·ha-1 (359.6 lb/acre). Yields generally were reduced as soil depth increased regardless of tillage type. The reduction in input for reduced-tillage would not compensate for the reduced yields for plants grown on the most productive soil depths.

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Planting date, fertilizer rate, and timing of harvest can affect yield of Jalapeño and banana peppers (Capsicum annuum L.). Seedlings of the Jalapeño `Mitla' and Long yellow wax `Sweet Banana #504' were transplanted in Apr. and July 1995 into beds fertilized with either a recommended or a higher rate. Fruit were harvested either three times or once, the latter corresponding to the last of several harvests. Significantly higher yields were produced from the July planting of both cultivars and with once-over harvesting. The recommended rate of fertilizer increased yield of `Sweet Banana #504' and decreased that of `Mitla' compared to the higher rate.

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Crop rotations can reduce problems that occur in monoculture planting systems. In 1990, at Lane, Okla., 0.5 ha of Bernow fine-loamy soil was planted to peanut (Arachis hypogaea L.). In the following 5 years, bell pepper (Capsicum annuum var. annuum L.), cucumber (Cucumis sativas L.), navy bean (Phaseolus vulgaris L.), and cabbage (Brassica oleracea L. Capitata group) were planted in one of four rotations after 1, 2, or 3 years of peanut. The first vegetable planting in each annual rotation was followed by either vegetables or peanut in following years. In 3 of the 6 years, peanut or vegetables were planted in each rotation. Peanut yields in the first year averaged 6.6 Mg·ha-1, but were <1.9 Mg·ha-1 thereafter. Yields of the first vegetable planting, which followed 1 or 2 years of peanut, were normal for this location, but were significantly lower after 3 years of peanut. For second or third plantings of vegetables in rotations, yields were reduced up to 50% compared to the first vegetable planting. For most crops, the rotation that had 3 years of peanut followed by 3 years of vegetables generally produced the least cumulative yield. Numbers of sclerotia produced by soilborne plant pathogenic fungi fluctuated over the years, but were the same in the spring of the second and sixth years. Rotating these crops appears to have limited applicability for maintaining high vegetable or peanut yields.

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This experiment was conducted to determine the effects of bed type (single or parallel raised bed vs. nonbedded); plant density (1991: ≈148,300 or 269,500 plants/ha; 1993: ≈148,300, 269,500, or 432,400 plants/ha); and use of black or white degradable mulch vs. nontreated soil on total and marketable yields and number of marketable seed per kilogram (seed count) of `Fleetwood', an erect bush, white-seeded navy bean (Phaseolus vulgaris L.). Spray-on mulch degraded before canopy closure, but a residue was present at harvest. In 1991, treatments did not affect yield or seed count. In 1993, bedding did not affect yield over nonbedded seedbeds. Black spray-on mulch increased marketable yield over plants grown with white spray-on mulch. Total and marketable yields were significantly higher at 269,500 than at 148,300 plants/ha. Bed type and plant density did not affect seed count, but seed count increased with black spray-on mulch. Dry beans should not be grown on beds under soil conditions such as those in our experiment. White spray-on mulch had no beneficial effect, but using black mulch needs additional evaluation. Planting at 269,500 plants/ha likely will yield ≈2 Mg seeds/ha in most years.

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Monoculture can lead to reduced yields due to pressure from biotic or abiotic sources. This pressure may be reduced by rotating crops. In the first year, a 0.5-ha of a Bernow fine-loamy, siliceous, thermic Glossic Paleudalf soil was planted to peanuts at Lane, Okla. In each of the following 5 years, the area was subdivided in to four rotations that were replicated four times. Bell pepper, cucumber, navy bean and cabbage were planted after 1, 2, or 3 years of peanuts. The first vegetable planting in each rotation was followed by either vegetables or peanuts, and these crops were planted in 3 of the 6 years in each rotation. Half of each plot was treated with soil fungicides, and half of the peanut plots were treated with foliar fungicides. Sclerotia, likely in the genera Sclerotia and Sclerotinia, were counted in the spring of each year starting in the second year. Peanut yields in the first year were 6.6 Mg·ha–1 but were <2.5 Mg·ha–1 thereafter. Yields of vegetables planted to follow 1 or 2 years of peanuts were normal for this location. Yields in later vegetable plantings in these rotations were reduced by 50%, and yields of vegetables planted after 3 years of peanuts were significantly less than vegetables planted after 1 or 2 years of peanuts. Numbers of sclerotia fluctuated over time, but numbers in the spring of the second year were the same as in the spring of the sixth year. The vegetables tested here should not be planted after >2 years of peanuts at this location.

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Delaying or limiting the number of harvests could improve yield and reduce inputs in bell pepper (Capsicum annuum var. annuum L.) production. Fruit were harvested in a variety of timing methods, which include three times over 14 days with the second and third harvests occurring 7 and 14 days after the first. Fruit from other plants were harvested once at either 7 or 14 days after the first harvest from plants that had several harvests. Fruit length was not affected by time of harvest. Number of marketable fruit, fruit width at the shoulder, endocarp thickness, and fruit volume were increased in fruit from plants harvested once. Marketable yields from plants with a single harvest were, on average, 1.5-fold higher than those from plants with several harvests. Delaying harvests improved fruit quality and quantity. Limiting number of harvests would reduce passes through the field and the associated costs, possibly improving net income.

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The efficacy of using potting media and fertilizers that are alternatives to conventional materials to produce vegetable transplants needs clarification. Bell pepper, onion and watermelon seed were sown in Container Mix, Lawn and Garden Soil, and Potting Soil, which can be used for organic production in greenhouse transplant production. The alternative media were amended with a 1× rate of Sea Tea liquid fertilizer. Comparisons were made to a system using a conventional potting medium, Reddi-Earth, fertilized with a half-strength (0.5×) rate of a soluble synthetic fertilizer (Peters). Watermelon, bell pepper and onion seedlings were lifted at 3, 6, and 8 weeks, respectively, and heights and dry weights determined. Watermelon were sufficiently vigorous for transplanting regardless of which medium and fertilizer was used. Bell pepper and onion at the scheduled lifting were sufficiently vigorous only if produced with conventional materials. Additional experiments were designed to determine the reason(s) for the weaker seedlings when the alternative products were used. Seedlings maintained in transplant trays, in which media amended weekly with Sea Tea were required to be held for up to an additional 34 days before being vigorous enough for transplanting. Six-week-old bell pepper, or 8-week-old onion, seedlings were transferred to Reddi-Earth in pots and supplied with Sea Tea or Peters fertilizer. Bell pepper treated with Peters were taller and heavier, but onions plants were similar in height and weight regardless of fertilizer used. Other pepper seed were planted in Reddi-Earth and fertilized weekly with Sea Tea at 0.5×, 1×, 2×, or 4× the recommended rate, or the 0.5× rate of Peters. There was a positive linear relationship between seedling height and dry weight for seedlings treated with increasing rates of Sea Tea. Other pepper seed were planted in to Potting Soil, or an organically certified potting medium (Sunshine), and fertilized with a 2× or 4× rate of Sea Tea or a 1×, 2×, or 4× rate of an organic fertilizer (Rocket Fuel), or in Reddi-Earth fertilized with a 0.5× rate of Peters. There was a positive linear relationship between the rate of Rocket Fuel and heights and dry weights of bell pepper seedlings. However, even at the highest rate seedlings were not equivalent to those produced with conventional practices. Plants treated with the 4× rate of Sea Tea were similar to those produced using conventional materials. Use of Sunshine potting medium and the 4× rate of Sea Tea will produce bell pepper seedlings equivalent in height and dry weight to those produced using conventional materials. The 4× rate of Rocket Fuel used in Sunshine potting medium will produce adequate bell pepper seedlings. The original poor showing of seedlings in the alternative potting media appears to be due to fertilization with Sea Tea at a rate that does not adequately support seedling development.

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