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Brian A. Kahn

Growers of turnip `greens [Brassica rapa L. (Rapifera Group)] are accustomed to planting 5.6 to 10 kg of seed per hectare. A study was conducted in 1985 to determine whether reduced plant populations could be used without reducing yield or quality for `Alltop', a hybrid cultivar with relatively expensive seed. A trial planted on 4 Apr. showed that populations could be reduced from 64 to 33 plants/m of row without reducing yield or quality. A second trial, planted on 30 Aug., used populations of 36, 26, and 16 plants/m of row. Again, there were no statistically significant reductions in yield or quality as populations decreased. However, yields from the 36 and 16 plants/m treatments differed by almost 7 t·ha-1, indicating substantial variability. A conservative approach would be to use a population of 33 to 36 plants/m of row (≈ 725,400 plants/ha) to provide a balance between seed costs and yield. This can be achieved by seeding rates of 2.2 to 2.8 kg·ha-1.

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Brian A. Kahn

Paprika pepper (Capsicum annuum L.) plants were subjected to a single, destructive harvest in either October, November, or December to determine an optimal month for once-over harvest. Studies were conducted at two locations in Oklahoma each year for 2 years. Total and marketable fruit yields were highest with October harvest dates in three of the four experiments. Marketable fruit red pigment intensity decreased between the November and December harvest dates at both locations in the second year. When the crop is established by transplanting, paprika harvest should be completed during October in the southwestern United States.

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Brian A. Kahn

Paprika pepper (Capsicum annuum L.) plants were subjected to a single destructive harvest in either October, November, or December to determine an optimal month for once-over harvest. Studies were conducted at two locations in Oklahoma each year for two years. Total and marketable fruit yields were highest with October harvest dates in three of the four experiments. Marketable fruit red color intensity decreased between the November and December harvest dates at both locations in the second year. It appears that paprika harvest should be completed during October in this region.

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Brian A. Kahn

This review summarizes studies involving intercropping for field production of peppers [Capsicum spp. (typically Capsicum annuum)]. Intercropping is particularly important in developing countries and where arable land is limited. Fruit crops, vegetables, forages, and other crops representing over 12 botanical families have been intercropped with peppers. System recommendations may be affected by whether one is attempting to grow another species as an intercrop in a pepper field or whether peppers are being used as an intercrop in a different primary crop. Other factors such as the timing of the intercrop planting, climatic conditions, and local economics all contribute to the potential success or failure of intercropping with peppers. Although broad recommendations cannot be made, the reviewed studies offer several examples of successful combinations of peppers with other crops.

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Brian A. Kahn

A 2-year study was conducted at Bixby, OK, to examine shoot characteristics of several eggplant (Solanum melongena) cultivars, including the vertical distribution patterns of fruit production, and to examine possible relationships of these traits to aspects of fruit quality. Plants of 11 cultivars of purple-fruited eggplant were field-grown following local production practices. Fourteen harvests of fruit that had reached horticultural maturity were made from 99 plants in each year over a period of ≈45 days per year. On each harvest date, every fruit that was harvested from an individual plant was charted. Before a fruit was severed from the plant, heights were measured from the soil surface to the pedicel attachment and to the blossom end. Each fruit was then weighed and categorized for marketability. On the day after the final harvest, each data plant was measured for height and diameter of the main stem and then severed at soil level for subsequent measurement of shoot dry weight. ‘Classic’, ‘Dusky’, ‘Megal’, and ‘Santana’ were the only cultivars that produced more than 50% marketable fruit in both years. There were no consistent relationships between plant height, stem diameter, or shoot dry weight and fruit quality. For a given cultivar, the fruiting plane was defined as the vertical space in which fruit were found over the course of the harvest period. This was delimited at the top by the mean height above the soil of the point of pedicel attachment and at the bottom by the mean height above the soil of the blossom end. The cultivars differed in fruiting planes, but height of fruit set was relatively unimportant as a determinant of overall fruit quality. Cull fruit usually had blossom ends that were higher off the ground than marketable fruit. The primary reason for cull fruit production was determined for two cultivars: ‘Black Beauty’ had poor fruit color and ‘Black Bell’ was relatively susceptible to fruit rot (primarily caused by Phomopsis vexans). Fruit scarring was found to be a major contributor to cull fruit production. Cultivars differed in fruit scarring in 1 of 2 years, and there was evidence that scarred fruit occurred higher in the crop canopy than marketable fruit.

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Clydette Alsup and Brian A. Kahn

Cowpea [Vigna unguiculata L. (Walp.)] cover crops were grown in a rotation with broccoli (Brassica oleracea L. var. italica Plenck.), spinach (Spinacia oleracea L.), and turnip greens [Brassica rape L. var. (DC.) Metzg. utilis] to evaluate the legume's ability to remove excess P from soils when poultry litter was used as a fertilizer. Fertilizer treatments were litter to meet each crop's recommended preplant N requirements (1X), litter at twice the recommended rate, and urea at the IX rate as the control. Following the vegetable crops, cowpeas were planted on half of each replication, while the other half was fallowed. The cowpeas were harvested for green-shell seeds and then underwent a simulated haying operation. Soil samples were taken at 0-to 15-cm and 15- to 30-cm depths at the onset of the study and after each crop to monitor plant nutrient levels. The cowpeas effectively lowered soil N levels but not soil P levels. However, there was no consistent evidence of an increase in soil P or K levels with litter applications. All three vegetable crops were successfully grown using poultry litter, although the 1X rate appeared inadequate for maximum production of broccoli and turnip greens.

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Brian A. Kahn and Wendy A. Nelson

Trellised plants of `Oregon Sugar Pod II' and `Snowflake' snow peas (Pisum sativum var. macrocarpon Ser.) were grown in single and double rows on l-m centers at a constant population of 20 plants/m2 in 1988 and 1990. Plants of `Oregon Sugar Pod II' produced a greater number and weight of fresh pods than plants of `Snowflake' in both years. Plants grown in double rows (10 cm within-row spacing) produced a greater number and weight of fresh pods than plants grown in single rows (5 cm within-row spacing) in 1988, but not in 1990. Vine dry weights were greater from plants grown in double rows than from plants grown in single rows in both years. Double rows seemed more promising for home gardeners than for commercial growers because of the increased branching and more widely scattered pod distribution on plants grown in double rows compared with plants grown in single rows.

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Judith L. Rose and Brian A. Kahn

Cowpea [Vigna unguiculata (L.) Walp.] was grown as a green manure preceding a fall crop of broccoli [Brassica oleracea L. (Italica Group)] in 1992 and 1993. Urea was used to supply 0, 84, or 168 kg·ha-1 of supplemental nitrogen (N) to broccoli which followed cowpeas. Control broccoli plots were grown on fallowed ground and were supplied with 168 kg·ha-1 of N from urea. Cowpea incorporation added over 100 kg·ha-1 of N to the soil in both years. In 1992, treatments had no significant effect on yield of marketable broccoli heads, but average head weight was reduced in the absence of external N. In 1993, broccoli yield was reduced following cowpeas except when 168 kg·ha-1 of external N also was supplied. Broccoli which followed cowpeas was delayed in maturity by 5 to 9 days in 1993. We conclude that a preceding cowpea crop alone will not supply enough N to sustain acceptable broccoli production. Further studies will determine how much external N must be supplied when broccoli follows cowpeas, and the best timing for supplying external N. We also will Investigate possible detrimental effects of the preceding cowpea crop on the broccoli.

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Brian A. Kahn and Daniel I. Leskovar

Studies were conducted to examine the effects of pruning treatments applied to spring-transplanted bell peppers (Capsicum annuum L.) on marketable fruit yield in late summer and fall. Control plants were set in the field in early May 1997 (Oklahoma) and Apr. 1998 (Oklahoma and Texas) and harvested weekly into October (Oklahoma) or periodically into December (Texas). In 1997, all four treatments (involving height and method of pruning) reduced total marketable fruit weight, but differences among treatments were nonsignificant. In Oklahoma in 1998, plants were mowed on 27 July at an average height of ≈24 cm. Mowed plants produced less total marketable fruit weight but more U.S. Fancy fruit than did control plants, while weight of U.S. No. 1 fruit was not affected. In Texas in 1998, plants mowed on 4 Sept. at a height of ≈20 cm produced more than twice the weight of U.S. No. 1 fruit and fewer cull fruit than did control plants. Nonpruned transplants set in the field in Summer 1998 (both Oklahoma and Texas) produced low marketable yields. Maintaining spring-transplanted bell peppers is a viable technique for fall pepper production, and the highest total marketable yields may be obtained if these plants are not mowed. However, mowing offers an opportunity for increased fall production of premium fruit, and mowed plants would be easier to manage than nonpruned plants.

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Brian A. Kahn and Mark E. Payton

Eggplants (Solanum melongena L.) were grown from transplants in a field study at Bixby, Okla., in 2005. Plants were harvested twice a week for 7 weeks. Data were taken from 3 individual plants per plot × 11 cultivars × 3 replications. The open-pollinated `Black Beauty' was inferior to the hybrids for yield and fruit quality. Patterns of cumulative percent marketable fruit number did not differ for 3 of the 4 cultivars producing the numerically highest (not always statistically highest) marketable fruit weights per plant (`Classic', `Nadia', and `Santana'). `Dusky' was the exception; fruit number peaked relatively early, but it still totaled among the highest for marketable fruit weight per plant. This might be considered an efficient fruiting pattern. Apart from `Dusky', a relatively high cumulative percent marketable fruit number throughout the season tended to be associated with an intermediate to low marketable fruit weight per plant. Two factors usually were responsible for this pattern: relatively low average marketable fruit weight, or high cull production. Despite significant differences in individual marketable fruiting patterns and average fruit weights, one relatively simple curvilinear model gave an excellent estimation of total and marketable eggplant fruit production (respectively) over time. The model was pct = 1/(1+exp(-(a+b*day))), where pct = estimated cumulative percent based on number of fruit, a = intercept, and b = slope.