LEVELS ON THE YIELD AND QUALITY OF RADISHES (Raphanus sativus L.) GROWN ON ORGANIC

Transcription

1 STEPHENS AND THOMPSON: RADISHES ON ORGANIC SOILS ment: "The evidence did not suggest that the deposit on the under-surface (sic) was increased in proportion to the deposit on the upper-surface (sic) of the leaf by electrostatic dusting" (2). The number of rates used in this study re sulted in more information on rate effects than did the bean study in which only two rates were compared. In all cases the 4 pounds per acre rate was no better than the 3 pounds per acre rate and the 3 pounds per acre rate when charged was much better than the 4 pounds per acre uncharged rate. It seems safe to conclude that if 4 pounds per acre is the normally ac cepted dusting rate for cabbage, dust require ments may be reduced to 3 pounds per acre (or by 25 percent) with charging with even better control than with uncharged dust at the higher rate. Sufficient data are not available from the bean experiment to support such a statement. However, it seems reasonable to assume that dust requirements may also be reduced about 25 percent for beans since beans reacted much the same way as did cabbage to electrostatic dusting. In both studies there were no differences in insect or disease control between positive and negative charging even though a slight trend existed in favor of negative charging. Deposition was much superior with negative charging than with positive charging. Therefore, to take ad vantage of this increased deposition due to a negative charge on the dust it is recommended that the charger be set to deliver a negative charge at the nozzle. Other reports have also indicated that negative charging seems more ef fective than positive charging and some manu facturers of electrostatic chargers now include in the instructions a recommendation that a nega tive charge be used. LITERATURE CITED 1. Casselman, T. W., P. L. Thayer and Wm. G. Genung. Electrostatic dusting in beans. Fla. State Hort. Soc. Proc. 2. Vickars, M. A. and F. T. Mesmer. Electrostatic dust ing of coffee trees in East Africa. Colonial Pesticides Re search Unit, Arusha, Tanganyika. Misc. Report No p THE EFFECT OF NITROGEN, POTASSIUM, AND MOISTURE LEVELS ON THE YIELD AND QUALITY OF RADISHES (Raphanus sativus L.) GROWN ON ORGANIC SOILS J. M. Stephens and B. D. Thompson Agricultural Extension Service Agricultural Experiment Station Gainesville Since 195, production and packaging of radishes have developed into an important eco nomic venture in Central and South Florida. The total acreage has risen from 1,831 acres in 1949 (3) to approximately 28,c)1 acres valued at over $3,5, in With such a rapid expansion, production prac tices in the radish fields have developed largely by trial and error. In Florida the majority of rad ishes are produced on muck soils which have been previously fertilized for such crops as sweet corn, lthe total acreage and value of radishes for the 196 season are based on growers' and County Agricultural Agents' acreage estimates and daily price data accumulated by the Florida Agricultural Extension Service. Florida Agricultural Experiment Stations Journal Series No endive, escarole and celery. Radishes are often grown foling such crops without any addi tional fertilizer. As a result of the differences in nutritional requirements and fertilization of the preceding crops, variations in fertility occur which may result in fluctuating radish yields and possible effects on quality. Materials and Methods Two experiments were conducted concurrently to determine the effects of three levels of nitro gen, three levels of potassium, and high and levels of moisture on the yield and quality of red, globe-type radishes. In the first experiment, conducted at Gaines ville, nine galvanized metal tanks were sunk into the ground, connected by % inch galvanized pipes for water-level control, and filled with raw, virgin peat soil from Florahome, Florida. Each tank measured 56 inches long, 4 inches wide, and 14 inches deep. The peat, which had an initial ph

2 14 FLORIDA STATE HORTICULTURAL SOCIETY, 1963 of 3.9, was limed to a ph of 6.9 to 7.1. The water level was maintained at ten inches be the soil surface. Three levels of nitrogen (, 5 and 1 pounds per acre as ammonium nitrate) in com bination with three levels of potassium (, 6, and 12 pounds per acre as sulfate of potash) were arranged randomly, using each tank as a plot and the entire tank system as a. The experiment was replicated through time by three successive plantings. At each planting, the fer tilizer treatments were broadcast; in addition every plot received a broadcast application of 12 pounds per acre of phosphorus (as super phosphate) and 25 pounds per acre of fritted trace elements. Fertilizer was incorporated into the soil to a depth of six inches. A measured volume of Cherry Belle radish seed was planted in four rows, 1 inches apart, per tank on November 7, 1961, January 15, 1962, and February 25, Plots were harvested 35 days after each planting. In the second experiment, Cherry Belle rad ishes were planted in October, 1961, January, 1962, and April, 1962, on mucky peat soil at the Central Florida Agricultural Experiment Station farm at Zellwood, Florida. Experimental design was a split-split plot replicated four times. In dividual plots were 15 feet long and 6 feet wide; each contained five rows spaced nine inches apart. The same fertility treatments and fertilizer sources as in the first experiment were used; however, the application of trace elements was omitted. The fertilizer was broadcast into the plots by hand and incorporated into the soil to a depth of six inches by a roto-tiller. One group of s was located in a portion of the field in which the water level was brought daily to the soil surface, constituting the high moisture level treatment. The "dry" group of s was located where the water table was maintained at about 2% feet be the soil sur face. In both experiments, soil samples were taken at each planting prior to fertilizing and analyzed for ph, available CaO, MgO, P2O5 and K2O at the Florida Agricultural Extension Service Soil Testing Laboratory, Gainesville. Results and Discussion Tank Experiment The yield of radishes, as total plant weight, total root weight, or weight of marketable size (over 5/8 inch diameter) per plot, was where either potassium or nitrogen, or both, were not added to the virgin peat. However, significant interactions occurred with the application of the various combinations. est yield of plant weight, root weight, and marketable-size root weight resulted for the med ium rate of nitrogen combined with the highest rate of potassium or the medium rate of potas sium combined with the highest rate of nitrogen (Table 1). Radish responses to additions of potassium were probably due to the initial level (Table 2) of potassium in the virgin peat. Millar (1) explained that such a level of potassium in peat is due to the high solubility of potassium in plant tissue. Responses to nitrogen were likely conditioned by factors, such as the (45-49 F) minimum temperatures during the grow ing periods, which were non-conducive to nitri fication of raw peat. Root elongation, cracking, and pithiness are manifestations of poor quality. The number of cracked per plot averaged about five per cent of the marketable-size, regardless of treatment. Applications of fertilizer which re sulted in increased yield of also resulted in increased yield of elongated (Table 1). However, about two per cent of the marketablesize at every treatment were elongated. From the results of this experiment, little can be deduced concerning pithiness, as 4 to 5 per cent of the in each plot contained some pithy tissue. Field Experiment. The greatest effects on the yield of radishes were due to time of planting and moisture level. Yield, as determined by total plant weight and by weight of marketable-size, was less (significant at the one per cent level) from the October crop than from either January or April crop (Table 3). Although the experiment was not designed where the two moisture levels could be statis tically compared, it was apparent that the yield of each crop was greater where the soil moisture level was high. Total plant weight increased from 12,848 grams per plot with the level of soil moisture to 14,664 grams per plot with the high soil moisture level. Weight of marketable-size increased from 6,538 grams per plot with the level of soil moisture to 8,172 grams per plot with the high level of soil moisture. The applications of nitrogen tested had no effects on the yield of radishes. With the level of soil moisture, yield was not affected by additions of potassium. Such would be expected due to the sufficient levels of potassium present,

3 STEPHENS AND THOMPSON: RADISHES ON ORGANIC SOILS 141 Table 1. Effect of nitrogen and potassium on the yield and quality of Cherry Belle radishes, Gainesville. Treatment pounds/a Total plant Grams Marketablesize ^ per plot1 Elongated Cracked N - K2O ,388 2,46 2,96 1,46 3,133 2, Q 1,231 1, ,528 1, Mean of three replications Roots over 5/8 inch in diameter Table 2. Results of soil-tests made on peat samples, Gainesville, and muck samples, Zellwood. Available nutrients, lbs./a Date sampled PH CaO MgO P9O5 KqO NO3 Gainesville March 22, very Zellwood Oct 17, ,867 2, ,68 1, Jan. 9, ,549 1,996 2,261-2, April 5, ,89-2, medium medium Incomplete value due to limitation of laboratory technique used to determine available CaO.

4 142 FLORIDA STATE HORTICULTURAL SOCIETY, 1963 as shown in the results of the soil-tests (Table 2). However, with the high level of soil moisture, there occurred an interaction significant at the 5 per cent level. From the high moisture level plots, yield of marketable-size increased from 7,88 grams per plot where no potassium was applied to 8,49 grams per plot with 12 pounds of potassium per acre. Montelaro and Jamison (2) suggest that lack of moisture in a soil can limit the amount of fertilizer that can be utilized efficiently by a plant; thus, it would ap pear that the failure of the radish plants to re spond to potassium applications on the dryer soil was due to insufficient moisture. Radish quality was affected by time of plant ing and soil moisture levels rather than by fer tilizer treatments. It was significant at the one per cent level that about 87 per cent of produced in April were elongated, whereas 12 per cent and 18 per cent were elongated in Janu ary and October respectively. However, an in teresting interaction occurred; only two per cent of the grown in October at the level of soil moisture were elongated, while 35 per cent were elongated that month with the high moisture level. While the October effect of soil moisture level on root shape seems unexplainable, such a high rate of elongation in April may be a re sponse to the longer day. The amount of cracking of radish seemed to be associated with high moisture levels (Table 3); however, its occurrence tended to decrease when conditions for rapid root growth, such as higher temperatures and longer days, prevailed. Summary Two experiments were conducted concurrently to determine the effects of three levels of nitrogen, three levels of potassium, and high and levels of soil moisture on the yield and quality of red, globe-type radishes. In the first experiment, carried out at Gaines ville in tanks filled with peat, it was found that total plant weight, total root weight and weight of marketable-size were where either potassium or nitrogen, or both, was not added to the virgin peat. est yield resulted from the medium rate of nitrogen combined with the highest rate of potassium or the medium rate of potassium combined with the highest rate of niotrgen. At every treatment about five per cent of the marketable-size were cracked and about two per cent were elongated. In the second experiment, conducted in the field on muck at Zellwood, greatest effects resulted from time of planting and soil moisture level. The October crop yielded less than either the January or April crop. The yield of each crop was greater where the soil moisture level was brought daily to the soil surface than when maintained at about 2^ feet be the soil sur- Table 3, Effect of time of planting and soil moisture on the yield and quality of Cherry Belle radishes, Zellwood. Planting time and soil Total Grams per Marketable- plotl Elongated Cracked moisture level plant size October 12,939 11,713 6,818 4,666 2, January 15,89 13,82 8,232 7,58 1,232 1, April 15,254 13,121 9,485 7,93 8,331 7, Mean of 4 replicates.

5 EVERETT: CUCUMBER FERTILIZER STUDIES 143 face. Applications of nitrogen had no effect on yield. Additions of potassium affected yield only where the soil moisture level was high. About 87 per cent of the produced in April were elongated, as compared with 12 and 18 per cent in January and October, respectively. Acknowledgements The authors wish to recognize with apprecia tion the assistance given by V. F. Nettles, J. Montelaro, D. F. Rothwell, R. B. Forbes, and P. J. Westgate in the development of this work. LITERATURE CITED 1. Millar, C. E Soil Fertility. John Wiley and Sons, Inc., New York. 2. Montelaro, J. and F. S. Jamison Commercial Vegetable Fertilization Guide. Fla. Agric. Ext. Ser. Circ. h W fter' J' C' 1952' Diseases of Vegetable Crops. McGraw-Hill Book Co., Inc. New York. MINOR ELEMENT AND NITROGEN STUDIES WITH CUCUMBERS Paul H. Everett South Florida Field Laboratory Immokalee The use of natural organic materials in fer tilizers has decreased over the past twenty-five years. Today many crops, particularly agronomic crops, citrus and some vegetables, are grown using all-mineral fertilizers. However, the suc cessful use of all-mineral fertilizers was accom panied or preceded by increased knowledge of the role of minor elements in plant nutrition and of the relationship between minor elements and natural organic materials. This was empha sized by Camp (1) and later by Sites (7) when they attributed the very poor condition of citrus groves, which was prevalent during the early 193's, to the use of all-mineral fertilizers with out the addition of minor elements formerly supplied in the organics. Although the trend is away from organics, they are still used to a great extent in fertilizers for high value produce crops. The reason most often given for the continued use of natural or ganics in mixed fertilizers is the reduction of ni trogen loss by leaching. However, as pointed out by Fiskell et al. (2) the primary benefit of or ganics probably is not due to the conservation of nitrogen but to other factors, such as acting as a buffer, supplying microbial media, serving as a source of soluble organic compounds for plant utilization, and the presence of minor elements in the. natural organic materials. The purpose of the foling studies was to determine if minor elements could account for Florida Agricultural Experiment Stations Journal Series No the yield response of cucumbers to fertilizers con taining natural organic materials. Materials and Methods Experiments were conducted during the fall season of 196, 1961 and 1962 using cucumber (Var. Ashley) as the test crop. Supplemental irrigation, by means of an open-ditch seep system, was used when needed. The plot areas for the three tests were all on Immokalee fine sand which had been cropped at least one time previously. The field plots were arranged in randomized s with four replications of each treatment. Three-row plots were used with the center row between treatments serving as a guard row. Cu cumber hills were spaced 18 inches apart in the drill on beds 5 feet apart. In 196 the hills were thinned to 1 plant and in 1961 and 1962 to 2 plants per hill. A fertilizer was applied at a rate equivalent to 3 pounds per acre. This was done in three applications of 1 pounds per acre each. One additional 1-poundper-acre application was made in the 1962 test. This was to compensate for nutrient loss caused by 1 inches of rain. A top dressing of 14 pounds of N and 12.5 pounds of K was applied to all plots 6 times in 196, 4 in 1961 and 2 in The nitrogen in the material used as top dressing was in the nitrate form. In 196, 1961 and 1962 the plots were harvested 12, 1 and 8 times, respectively. The 1962 experiment was terminated prematurely by a freeze which occurred on De cember 13. Nitrogen Sources. Two basic fertilizers, both with a formulation, were used in the three experiments. One contained 3% natural organic nitrogen (Fertilizer No. 1) and the other 1% inorganic nitrogen (Fertilizer No. 2). The nitro-