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  • Author or Editor: J.T. Garrett x
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Yield and quality responses of `Market Prize' cabbage to five nitrogen sources and five rates of each source were measured in a replicated test at Clemson and Florence, SC in 1987 and 88. Soil nitrate solution, analyzed by the ion-electrode method, was monitored bi-weekly with maintenance levels kept throughout the growing season at or above threshold levels of 5, 10, 15, 20, and 30 ppm. The 15-0-14 (nitrate of soda/potash) gave higher total and early yields; higher levels of soluble solids and dry weights when compared to other N-sources of sodium-, ammonium-, potassium-, and calcium nitrate. Uptake, as measured by leaf tissue nitrate ion concentration, increased across soil solution levels up to 20 ppm.

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Nitrogen from five different sources applied preplant and sidedress to field grown watermelon (Citrullus lanatus Thunb. cv. Prince Charles) did not affect total yield but more melons were harvested earlier when potassium nitrate or calcium nitrate was applied frequently in small amounts. Conversely, two sidedressings of ammonium nitrate or soda/potash applied at 30-day intervals outperformed other application frequencies for these sources. Timing of application had little effect on earliness when sodium nitrate was the source. Improvement in percent stand was documented where total nitrogen fertilizer was applied frequently in small amounts versus infrequent larger amounts. Stand count improvements approached 30 percent for ammonium nitrate and potassium nitrate when amounts were split over five applications versus the single application. Soluble solids and flesh color were not affected by treatments used in this study.

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Winter production of collard and kale (Brassica oleracea L. Acephala Group) in the southeastern United States is limited by the tendency of these leafy green vegetables to bolt following vernalization. Collard and kale cultivars, landraces, and breeding lines were tested in four winter environments from 1992 to 1995 to determine differences among all included entries for winter production and tendency to bolt in a cold season environment. Essentially all entries survived the conditions of four winter environments. However, whether an entry reached harvest size depended on its date of 50% bolting. Collard typically bolted earlier than kale. Most kale entries reached a marketable size before bolting, while only the collard cultivars `Blue Max' and `Champion' and landraces G. Summersett and Mesic Zero consistently did the same. Several entries, for example, `Squire' kale and G. Summersett collard, usually did not bolt. Results of this research indicate that significant genetic control of the long-standing (delayed bolting) phenotype is present in collard and kale. Successful winter production of these cole crops can be better ensured by using a long-standing genotype.

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`Jewel' sweetpotato was no-till planted into crimson clover, wheat, or winter fallow. Then N was applied at 0, 60, or 120 kg·ha–1 in three equal applications to a sandy loam soil. Each fall the cover crop and production crop residue were plowed into the soil, beds were formed, and cover crops were planted. Plant growth of sweetpotato and cover crops increased with N rate. For the first 2 years crimson clover did not provide enough N (90 kg·ha–1) to compensate for the need for inorganic N. By year 3, crimson clover did provide sufficient N to produce yields sufficient to compensate for crop production and organic matter decomposition. Soil samples were taken to a depth of 1 m at the time of planting of the cover crop and production crop. Cover crops retained the N and reduced N movement into the subsoil.

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A 5-year study using winter cover crops (wheat or rye, crimson clover, and fallow) in a tomato and bean rotation indicated several soil responses to the cover crops. Advantages of crimson clover winter cover crop to the soil in a tomato-bean rotation included adding organic matter to the soil, which resulted in an increase in the amount of inorganic nitrogen in the upper levels of the soil profile and an increase in the soil's water-holding capacity. An additional benefit of winter cover crops to the soil was the potential of reduced nitrogen leaching.

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Cucumber and potato crops were tested in a rotation with winter cover crops at different locations in Georgia, North Carolina, and South Carolina from 1991 to 1994. Biomass DM of vegetable crops was greatest when grown after crimson clover. Clover plantings resulted in a greater biomass than wheat when preceded spring cucumber crop. Vegetable biomass produced on clover plots or with N rates of 60 to 120 kg·ha–l was equivalent. Nitrogen recovery by cover and vegetable crops was enhanced by clover plantings. Clover biomass (tops only) provided an average of 138 kg N/ha for the cucumber crop, compared to an average of 64 kg N/ha provided by wheat. Nitrogen recovery by vegetable crops was also enhanced with 60–120 kg N/ha rates. Yields were highest when high N rates were used and when crops were produced on clover plots. Vegetable yield, cover crop biomass, and N recovery were positively correlated with vegetable biomass and applied N.

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A vegetable production system using winter cover crops and N rates was evaluated for several years in Georgia, South Carolina, and North Carolina. Snap bean, cucumber, tomato, potato, and sweetpotato crops were tested at different locations. Cover crop plots produced higher yields and better quality in all locations as seasons progressed over 4 years. Soil N levels in fallow, wheat, and clover plots were similar at initiation, but N gradually increased in clover plots in successive years. Yield and quality of root crops improved with Crimson clover without N applications compared to fallow plots with 60 kg N/ha. Effects on yield and tuber size are discussed. Nitrate and NH4-N in the soil profile from 15- to 150-cm depth were monitored at all locations. Nitrogen availability, depletion, and leaching below the root zone were determined. At low N rate, clover plots had slightly higher NO3 in the soil profile; however, at high N rate, N supply by clover was not as critical, and N leaching was detected at much lower depths than at low N rates.

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Tomatoes and beans were grown in rotation for 4 years with three cover crop treatments (bareground, wheat, and crimson clover) and three nitrogen rates (0, 60, and 120 kg N/ha). Over the course of the study, when no additional N was provided, lowest yields of tomatoes and beans were obtained with the wheat cover crop. With the highest N rate, however, there was little difference in yields of beans or tomatoes with any of the cover crop treatments. Considering the benefits associated with the use of cover crops, it is encouraging to see that with proper N amendment, yields obtained with cover crop systems can be comparable to conventional bareground systems.

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Abstract

‘Champion’, ‘Georgia’, ‘Heavicrop’, and ‘Vates’ collards (Brassica oleracea L. var acephala) were planted in Fletcher and Lewiston, N.C.; Charleston, Clemson, and Florence, S.C.; and Attapulgus and Plains, Ga. to determine the most reliable method to predict harvest maturity based on temperature. Although cultivar differences existed within some of the planting dates, when pooled over all planting dates, cultivars yielded similarly within locations. Eight methods of calculating heat units from planting to harvest were applied to daily maximum and minimum air temperatures supplied from local weather bureaus for the spring and fall growing seasons from 1985 through 1987 in the three-state area. Coefficients of variation were used to determine which method was most reliable in predicting day of first harvest. The method with the lowest cv was to sum, over days for planting to harvest, the difference between the daily maximum and a base temperature of 13.4C; however, if the maximum was >23.9C, the base temperature was subtracted from an adjusted maximum equal to 23.9C minus the difference between the maximum and 23.9C. This method produced a cv of 9.1% compared to 11.4% for the standard method of summing the mean temperature minus the base of 4.4C over the entire growing season, or compared to 13.4% for counting days to harvest from planting.

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