Factorial combinations of two row arrangements on 1.8-m-wide beds (either four rows, each 30 cm apart, or eight rows, each 15 cm apart) and two in-row seeding rates (either 48 or 96 seeds per 30 cm of row) were compared on ‘Santo’ cilantro (Coriandrum sativum L.) in five experiments at Bixby, OK. Plots were harvested once per experiment by cutting at a height of ≈7 cm with a small-plot greens harvester, and fresh weight yields were taken. Treatments minimally affected canopy height at harvest. Eight rows resulted in higher yields than four rows in three of five experiments. Main effects of seeding rate or interactions of row number and seeding rate on yield were rare. Of the four combinations tested, the eight-row arrangement sown at 48 seeds per 30 cm would be recommended. This arrangement was used in three other experiments to test effects of a single preharvest spray application of gibberellic acid (GA). Treatments were a water control and GA at either 10 or 20 g·ha−1. Treatment with GA increased bolting in a 17 Apr. planting and increased canopy height at harvest in two of three experiments. However, GA treatments did not affect yield. Treatment with GA would not be recommended for a spring cilantro crop and may have limited impact on increasing machine recovery of raw product in a fall crop.
Brian A. Kahn and Niels O. Maness
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.
Brian A. Kahn and Judith L. Schroeder
Field experiments were conducted in Oklahoma in 1993 and 1994. Cowpeas [Vigna unguiculata (L.) Walp.] were grown using either noninoculated seed and 23 kg·ha–1 of preplant nitrogen (N) fertilizer (conventional) or Rhizobium-inoculated seed and no preplant N fertilizer (reduced input). Sample plants were excavated at first pod set and analyzed for nodulation and root morphology. Additional plants were harvested at the green-shell stage to determine seed yield and plant N concentration. Conventional and reduced input cowpeas did not differ in dry weight of root mass components, total root dry weight, shoot dry weight, shoot: root ratio, nodule distribution among root morphological components, total nodule fresh weight, plant N concentration, or green-shell seed yield. Most of the nodule fresh weight generally was associated with nodules on the basal and lateral roots. Results indicate that cowpea root characteristics are not necessarily altered by the presence or absence of added N fertilizer at a given location.
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 were harvested weekly into October (Oklahoma) or periodically into December (Texas). In 1997, there were no differences in total marketable fruit weight among four treatments involving height and method of pruning, but all reduced total marketable fruit weight relative to the control. In Oklahoma in 1998, the control was compared to plants 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 control plants. Also, control and mowed plants did not differ in weight of U.S. no. 1 fruit. In Texas in 1998, the control was compared to plants mowed on 4 Sept. at a height of ≈20 cm. Mowed plants produced more than double the weight of U.S. no. 1 fruit and fewer cull fruit than control plants. Nonpruned transplants set in the field in Summer 1998 (Oklahoma and Texas) gave low marketable yields. Maintaining spring-transplanted bell peppers is a viable technique for fall pepper production, and the highest total marketable yields may occur 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 unpruned plants.
Brian A. Kahn and Judith L. Schroeder
Field experiments were conducted in Oklahoma in 1993 and 1994. Cowpeas [Vigna unguiculata (L.) Walp.] were grown using either non-inoculated seed and 23 kg·ha–1 of preplant nitrogen fertilizer (conventional) or inoculated seed and no preplant nitrogen fertilizer (reduced input). Sample plants were excavated at first pod set and analyzed for nodulation and root morphology. Additional plants were excavated at the green-shell stage and were analyzed for nitrogen concentration. Conventional and reduced input cowpeas did not differ in nodule distribution among root morphological components, total nodule fresh weight, total root dry weight, or nitrogen concentration. Most nodules generally were located on the basal and lateral roots. Results indicate that cowpea root characteristics are not necessarily altered by differing cultural systems at a given location.
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.
Brian A. Kahn and Lynn P. Brandenberger
Field studies were conducted in Oklahoma from 2010 to 2012 to develop protocols for fall sweet corn (Zea mays) production. Variables examined included a transgenic cultivar that expresses the CryIA(b) toxin from the bacterium Bacillus thuringiensis (Bt) and its nontransgenic near-isoline, seeding rates and planting dates, and various insecticide regimens. We found that, in eastern Oklahoma, a suitable planting window would correspond roughly to the last 2 weeks in July. Within this favorable period and given timely irrigation, it was possible to sow corn to an acceptable stand. A seeding rate ≈1½ times the desired final stand of one plant/ft appeared to be satisfactory. Use of a cultivar (GSS-0966) with genetic resistance to lepidopteran pests was a critical factor for successful production of fall sweet corn. Efforts to produce a crop with a nontransgenic cultivar using insecticides with relatively low mammalian toxicity were unsuccessful. Our experiments support previous recommendations for applying supplemental insecticides to transgenic Bt sweet corn to potentially increase production of “premium” ears by reducing the percentage of ears with severe insect damage (damage >1½ inches from the cob tip). We demonstrated that a spray schedule that rotated two insecticides with intermediate mammalian toxicity (carbaryl and permethrin) was as effective in reducing severe insect damage to ears of ‘GSS-0966’ as a similar schedule that rotated two highly toxic insecticides (esfenvalerate and methomyl).
Brian A. Kahn and Peter J. Stoffella
Seeds of `Rutgers California Supreme' tomato (Lycopersicon esculentum Mill.) were exposed to outer space conditions aboard the long duration exposure facility (LDEF) satellite in the space exposed experiment developed for students (SEEDS) project of the National Aeronautics and Space Administration (NASA). Seeds aboard the LDEF were packed in dacron bags forming four layers per sealed canister. Some of these seeds were used in Oklahoma and Florida for studies of germination, emergence, and fruit yield. Among all measured variables in three experiments, there was only one significant main effect of canister 2 versus canister 7 (for mean time to germination) and only one main effect of layer (for seedling shoot dry weight). There also were only two inconsistent canister x layer interactions in the germination tests. The contrast of Earth-based control seed versus space-exposed seed was significant four times: in Oklahoma in 1991 the mean time to germination of space-exposed seeds and the days to 50% of final germination were 0.7 days less than for Earth-based seeds, and in Florida in 1992 seedling percent emergence and shoot dry weight were increased by space exposure. Fruit yield and marketability were unaffected in plants grown from space-exposed seeds. These results support student findings from the SEEDS project, and provide evidence that tomato seeds can survive in space for several years without adverse effects on germination, emergence, and fruit yield.
Brian A. Kahn and Raymond Joe Schatzer
The herbicides paraquat, trifluralin, and metolachlor were compared for efficacy of weed control in cowpea [Vigna unguiculata (L.) Walp.] with and without cultivation as a supplemental strategy. Herbicides also were compared against a no cultivation-no herbicide treatment (control) and against cultivation without an herbicide. Cultivation had no significant effect on seed yield, biological yield, or harvest index of cowpea. Paraquat, applied before seeding but after emergence of weeds, was ineffective for weed control and usually did not change cowpea yield from that obtained without an herbicide. Trifluralin and metolachlor more than tripled cowpea seed yield compared with that obtained without an herbicide in 1988, when potential weed pressure was 886 g·m-2 (dry weight). The main effects of trifluralin and metolachlor were not significant for cowpea seed yield in 1989, when potential weed pressure was 319 g·m-2 (dry weight). However, in 1989, these two herbicides still increased cowpea seed yield compared with that of the control and increased net farm income by more than $300/ha compared with the income obtained from the control. Chemical names used 1,1'-dimethyl-4,4' -bipyridlnium salts (paraquat); 2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl) benzenamine (trifluralin); 2-chloro-N-(2-ethyl-6 -methylphenyl)-N-(2-methoxy-l-methylethyl) acetamide (metolachlor).
Brian A. Kahn and Peter J. Stoffella
Field experiments were conducted in 1985 at Fort Pierce, Fla., and Bixby, Okla., to quantify and describe the distribution of nodules among root morphological components of cowpea [Vigna unguiculata (L.) Walp.]. Plants of `Knuckle Purplehull', `Mississippi Cream', and `White Acre' were sampled by cultivar on separate dates at three growth stages: pre-anthesis, seed initiation, and harvest, when most pods were dry. Root masses were partitioned into adventitious, basal, lateral, and taproot components. Nodules were removed from roots, grouped according to root morphological component of origin, and weighed. No linear correlation was found between the weight of a particular root morphological component and the nodule weight associated with that component. Total root weight and total nodule weight also were not strongly correlated. Nodule weights usually were lower at harvest than at earlier stages of ontogeny, especially for nodules from taproots. Although ≈70% of the root mass was in the taproot and its associated laterals at both locations, the taproot per se was not the primary locus of nodulation. Instead, most nodules generally were located on the basal and lateral roots. When percentage distribution of total nodule weight was examined, neither growth stage nor cultivar was found to affect nodulation of basal or lateral roots.