MINOR ELEMENT AND NITROGEN STUDIES

Transcription

1 EVERETT: CUCUMBER FERTILIZER STUDIES 3 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 roots produced in April were elongated, as compared with 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 rtility. John Wiley and Sons, Inc., New York. 2. Montelaro, J. and F. S. Jamison Commercial Vegetable rtilization 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 1930'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 following 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 1960, 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 blocks with four replications of each treatment. Three-row plots were used with the center row between treatments serving as a guard row. cumber hills were spaced 18 inches apart in the drill on beds 5 feet apart. In 1960 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 3000 pounds per acre. This was done in three applications of 1000 pounds per acre each. One additional 1000-poundper-acre application was made in the 1962 test. This was to compensate for nutrient loss caused by 10 inches of rain. A top dressing of pounds of N and.5 pounds of K was applied to all plots 6 times in 1960, 4 in 1961 and 2 in The nitrogen in the material used as top dressing was in the nitrate form. In 1960, 1961 and 1962 the plots were harvested, 10 and 8 times, respectively. The 1962 experiment was terminated prematurely by a freeze which occurred on De cember 13. Sources. Two basic fertilizers, both with a formulation, were used in the three experiments. One contained 30% natural organic nitrogen (rtilizer No. 1) and the other 100% inorganic nitrogen (rtilizer No. 2). The nitro-

2 4 FLORIDA STATE HORTICULTURAL SOCIETY, 1963 gen fraction of the two fertilizers was derived as follows: rtilizer No units from Peruvian guano and sludge 1.0 unit from sodium nitrate 1.8 units from ammonium sulfate and ammoniated superphosphate rtilizer No units from ammonium nitrate. Inasmuch as No. 1 contains several inorganic nitrogen carriers in addition to the organics whereas No. 2 had only a single nitrogen carrier, a commercially mixed 100% inorganic nitrogen fertilizer was included in the 1961 test. The nitrogen fraction in this fertilizer (No. 2A) was derived as follows: 1.2 units from ammonium nitrate and sod ium nitrate. 2.8 units from ammonium nitrate, ammon ium sulfate and ammoniated super phosphate. Minor elements. No minor elements (m.e.) were used in any treatment in The source of m.e. in 1961 was FN-501, a fritted material con taining.3%, 4.7% Zn, 2.0%, 2.0% B and 0.13% Mo. One half of the plots received FN-501 at a rate equivalent to pounds per acre along with the first application of fertilizers No. 1, No. 2 and No. 2A. The remaining plots received the fertilizers but no FN-501. Thus, each of the three fertilizers was applied with and without FN-501. In 1962 and were tested either in a chelated form or in a soluble salt form. and, in both forms, were used in combination with fertilizers No. 1 and No. 2. Other treatments were fertilizer Nos. 1 and 2 with and without chelating agent but not with m.e. and were applied at a rate equivalent to 20 pounds per acre of FN-501. This repre sents 0.4 lbs. /A and 2.5 lbs. /A. pric sulfate (S04. 5 H2O) and ferrous sulfate ( S04. 7 H2O) were chelated in the proper amounts with Na4 EDTA according to the manu- Table 1. The effect of nitrogen source on marketable yields of cucumbers. 30% org.-n 100% inorg. -N 100% inorg. -N L.S.D. L.S.D. 5% level 1% level rt. No A Year 1961 (bu./a) facturers' recommendation. Where the chelating agent was used without either or, 500 ml of a solution containing 0. gm. Na4EDTA/ml was applied to the appropriate plots. Where the m.e. was used as a soluble salt the desired amount was dissolved in distilled water. All treatments were made by spraying an 18-inch wide band down the center of a false bed and then bedding over to a depth of 3 inches. This was done at the time of the first fertilizer application in order for the spray to come in contact with the fertilizer bands. No m.e. were included in subsequent fertilizer applications. Soil and plant tissue samples from the three experiments were taken periodically for chemical analyses. After liming, but before applying fertilizer, the soil ph in the plot areas was 6.8, 6.2 and 6.5 in 1960, 1961 and 1962, respectively. Results There was a highly significant yield increase (Table 1) during each of the three years from plants receiving part of their nitrogen from natural organics. The magnitude of the yield increase varied with years and was greatest in 1960, when visual differences in vine growth between plants fertilized with 30% organic-n and those fertilized with 100% inorganic-n were very obvious. The plants receiving the all-mineral fertilizer exhibited a stunted appearance with the leaves showing a marginal burn. This con dition was first observed three weeks after plant ing and persisted throughout the remainder of the season. Differences in N, P, K, Ca, ph and total soluble salts of soil samples from the various treatments were not great enough to account for the growth and yield differences. However, an alyses of plant tissue (Table 2) indicated that the content of,, Mn and B was much higher and aluminum (Al) much lower where the natural organics were used. With the excep tion of Al, there was the same relationship for m.e. content in the two fertilizers (Table 2). The m.e. composition of cucumber leaves for the 1961 experiment is shown in Table 3. The yield increase was highly significant where nat ural organics were used. The only significant yield increase due to added m.e. was with ferti lizer No. 2A. With this fertilizer plus m.e. the yield was 908 bu./a. and without m.e., 788 bu./a. The and levels in plants receiving the organics were higher than in plants fertilized with either of the two all-mineral fertilizers. The, and Mn contents of leaf samples reflected the

3 EVERETT: CUCUMBER FERTILIZER STUDIES 5 Table 2. Minor element composition* of dry cucumber leaves and of fertilizer used where a yield response to organic-nitrogen was found (1960). Minor Plant Samples** Difference rtilizer** Difference element A B (A-B) 1 2 (1-2) ppra Iron Copper Manganese Boron N.D. 60 Aluminum ^Analysis by D.C. Arc with rough estimates precision. **A - plants fertilized with % organic-n (fertilizer No.1) B - plants fertilized with * inorganic-n (fertilizer No. 2). addition of m.e. in combination with fertilizers taining organics did not significantly increase Nos. 1 and 2A but not No. 2. yields over that obtained.with the fertilizer alone. Table 4 shows the effect of the different treat- Although the yield with chelated was ments on cucumber yields for the 1962 experi- higher than with as a soluble salt, the differmeivt. The data shown in Table 4 result from ence between the two treatments was not sigthe interaction N-source x m.e. x chelating agent. nificant. When the all-mineral fertilizer was When the fertilizer containing natural organics used there was no significant yield response to was used, the addition of chelating agent alone, addition^ of or either chelated or soluble, chelated or soluble resulted in significant or to chelating agent alone. yield increases over the yield obtained with this The individual effect of nitrogen source, m.e. fertilizer alone. However, the addition of either and chelating agent, and the interaction effect chelated or soluble to the fertilizer con- of nitrogen source x chelating agent on yields Table 3. The effect of nitrogen source and FN-501 on marketable yields of cucumbers and on minor element composition of dry cu cumber leaves (1961). rt. FN-501* Yield Leaf composition () source No. lbs*/a. Bu./A. Mn B Al 30% org.-n % 100% inbrg.-n inorg.-n L.S.D. for L.S.D. for A N-source 5% level 1% level minor element 5% level 0 1% leve? N.S *FN a fritted material containing, Mn,, Zn, B and Mo,

4 .. 6 FLORIDA STATE HORTICULTURAL SOCIETY, 1963 Table 4. The interaction effect of nitrogen source, minor element and chelating agent on marketable yields of cucumbers (1962). source 30% org. 100% inorg. L.S.D. 5% level 1% level Minor ele. Chelate (bu/a) are shown in Table 5. The individual effect of the chelating agent on yield was not significant but in combination with the fertilizer containing 677 natural organics it resulted in a highly signifi cant increase in yield. The composition of cucumber leaves from plants receiving the various treatments in the 1962 experiment is shown in Table 6. The re sults on the two sampling dates cannot necessarily be compared directly because the analyses were made in different laboratories and in most cases by different analytical procedures. However, comparisons can be made of values within each sampling date. The first sampling was made when the plants were young (3 or 4 true leaves). The*average content was the same for plants receiving either organics or all-mineral fertilizer. The average content was slightly higher and the Ca, Mg and P content slightly lower, but Mn was approximately 40% higher when organics were used in the fertilizer. The addition of and whether chelated or in the soluble-salt form made little difference in the content of these elements in the plant tissue. On the later sampling date there was little difference in the,, Mn or Mg content of plants receiving either organics or all-mineral fertilizer. The Ca was somewhat higher and P slightly lower in plants fertilized with organics. Chelation of and had little effect on the plant uptake of these elements. Discussion In 1960, when the greatest differential oc curred in yield and vine growth between plants receiving a fertilizer containing 30% natural organic-n and those receiving and all-mineral fertilizer, spectrographic analyses (Table 2) showed a direct relationship between the m.e. content of the fertilizers and the m.e. content of plants receiving these fertilizers. From this it seemed very likely that the yield response was due to the m.e. contained in the natural organics. Another aspect which may be a factor in ex plaining the striking response, both in vine growth and yield, was the behavior of Al.' The all-mineral fertilized contained only one-half as much Al as the fertilizer containing organic-n, but the leaves of plants grown with the former fertilizer contained 6 times more Al than did the leaves of plants fertilized with the latter. Although this may be a Steenbjerg effect (8) in which increased growth dilutes increased nutrient uptake, the increased growth with organics was not associated with a decreased content of the other m.e. The high content of Al in the leaves indicates the possibility of Al toxicity. It is suggested that the decreased absorption of Al by plants fertilized with natural organics may have resulted from either the presence of other m.e. in amounts sufficient to compete with Al, or Table 5. The individual effect of the three var iables and the interaction effect of nitrogen source x chelating agent on the average marketable yields of cucumbers (1962). Minor N-source source bu./a. element bu./a. Chelate bu./a. x chelate bu./a. 30% org.-n org. che % inorg.-n che inorg.che che. 698 L.S.D. 5% level 38 L.S.D. 1% level N.S. N.S. 54

5 EVERETT: CUCUMBER FERTILIZER STUDIES 7 Table 6, Interaction effect of nitrogen source, minor elements and chelating agent on the composition of dry cucumber leaves at two sampling dates (1962). Minor Chelate source element (Na^EDTA) Mn P Mg Ca 30% organic (October ) Av. for 30% org % inorganic Av. for 100% inorg. 30% organic (November ) Av. for 30% org & % inorganic Av. for 100% inorg the presence of some substance associated with the organics, such as a natural chelating agent (3), which reduced the absorption of Al without decreasing the uptake of other m.e. Certain artificial chelating agents have been reported (6, 10) to overcome the effects of heavy metal toxicity and this was attributed in part to decreased absorption of the heavy metal. It seems that a naturally occurring chelating agent may react in a similar manner. The benefit from the addition of a complete m.e. mixture to the fertilizers in 1961 was not apparent when the fertilizer contained natural organics. This indicates that either the organics

6 8 FLORIDA STATE HORTICULTURAL SOCIETY, 1963 were supplying sufficient m.e. or that the plants were not absorbing m.e. from the added mixture. The first of these two possibilities appears more likely because the,, Mn and B content of leaves from plants receiving organics plus the m.e. mixture was higher than those from the corresponding treatment without added m.e. Natural organics have been reported (2) to in crease the availability of and Zn to water melon plants. The results with the 2 all-mineral fertilizers were somewhat conflicting. With one (fertilizer-no. 2A) there appeared to be a re sponse to the added m.e., both in yield and leaf composition, where as with the other (rtilizer- No. 2) this response was not evident. In contrast to the 1960 experiment there was little difference in vine growth among any of the treatments used in This was also true for the leaf content of Al; which further indicates that Al toxocity could have been responsible for the poor vine growth with the all-mineral fer tilized used in The fact that Al toxocity did not appear to be a factor in the 1961 and 1962 results may have been due to the relocation of the plot area following the 1960 experiment. Thus the soil in the areas used in 1961 and 1962 may have been lower in Al and/or conditions less favorable for Al absorption by the cucumber plants. The data from the 1962 experiment (Tables 4 and 6) indicate that it was not necessarily the lack of and in the all-mineral fertilizer that was responsible for the lower yields obtained when this fertilizer was used. If this had been the case, both the yields and leaf content of and from treatments receiving these elements in combination with the all-mineral fertilizer would probably have been higher than the yields and leaf content of and from the cor responding treatments without these elements. Manganese may have been involved in the yield differences obtained with the two fertilizers used in this experiment. Prior to the first sampling, the fungicide maneb had not been used; thus the leaf Mn was derived from the soil and fertilizer. The higher leaf content of Mn in plants receiving organics indicates plant uptake of the Mn contained in the organics in addition to the Mn originally in the soil. Shortly after the first sampling date maneb was included in the diseasecontrol program for the remainder of the crop season. The use of this fungicide, which contains Mn, is reflected at the second sampling date in the rather high leaf Mn of plants receiving either the organics or the all-mineral fertilizer. It is questionable whether the lower leaf Mn during the early growth stage of plants receiving the all-mineral fertilizer could have exerted sufficient influence on the physiology of the plant to account for the yield differences. However, this is a possibility. The high values for leaf in plants from all treatments on the second sampling date prob ably resulted from drift of sprays used for disease control on tomatoes in an adjacent plot area. This was evident by the fact that the leaf in plants from the two replications nearest the tomato plots was approximately twice that in plants from the two replications further from the tomatoes. This factor could have masked any effect from the treatments used in the 1962 experiment. A stimulating effect on yield by the chelating agent (Na4EDTA) when in combination with the fertilizer containing natural organics was observed. From the plant tissue analyses it does not appear that this stimulation was due to in creased availability of any of the plant nutrients tested. Perhaps the stimulatory effect was due to the chelating agent per se. EDTA has been observed to result in yield increases supposedly beyond its ability to supply deficient minor ele ments to plants (4, 5, 11). Several reasons have been suggested for this, but as mentioned by Wallace (9) there is at present insufficient evi dence for accepting or rejecting any one of the possibilities as the only cause. It should be pointed out that in the present study this stimu latory effect was not evident when the chelating agent was in combination with the all-mineral fertilizer. The results of these experiments indicate that there is an association between the minor elements contained in natural organics and the increased yields obtained when fertilizers con taining these materials are used for cucumber production. They also indicate that minor ele ments, at rates tested, may not be the primary reason for this response, since an all-mineral ferti lizer supplemented with minor elements did not produce yields comparable to those obtained with organics. Evidence from soil and plant tissue analyses suggests that leaching of soil N and K was not a major factor and that plant uptake of these two elements was comparable from either the all-mineral fertilizer or the fertilizer con taining natural organics. As mentioned elsewhere in this paper there remain several other possible explanations for the response to organics observed frequently

7 SUTTON: OKRA FERTILIZATION 9 in this area and less frequently in other areas. As yet, none of these has been thoroughly in vestigated. ganic-n fertilizer plus a chelating agent gave a higher yield than plants receiving the same fertilizer but without the chelating agent. Summary Field studies with cucumbers were conducted during 1960, 1961 and 1962 in order to measure the yields from fertilizers containing 30% or ganic nitrogen as compared to yields from allmineral fertilizers. Data from the 1960 experi ment indicated that minor elements could have been involved in the results obtained. Therefore, various forms (fritted, soluble salt and chelated) of minor elements were included in 1961 and In 1960 significantly higher cucumber yields were associated with the 30% organic-n fertilizer. Chemical analysis of this fertilizer revealed that the minor element content was considerably higher than that in the all-mineral fertilizer. The same was true for leaf samples taken from plants grown with the organic-n fertilizer. There was a significant yield increase in 1961 due to both organic nitrogen and a fritted source (FN-501) of minor elements. In 1962, chelated and soluble salts of iron and copper in combination with a 30% organic-n fertilizer and with an all-mineral fertilizer were compared. Higher yields were associated with all treatments that were in combination with the 30% organic-n fertilizer. There was a yield response to both forms of iron but not to either form of copper. Plants receiving the 30% or Acknowledgments Appreciation in expressed to Dr. J. G. A. Fiskell of the Department of Soils, Florida Agri cultural Experiment Stations, for the spectrographic analyses and many of the chemical an alyses of plant tissue samples; and to Dow Chemical Company for supplying the Na4EDTA (Versene-100) used in the 1962 experiment. LITERATURE CITED 1. Camp, A. F. A resume of feeding and spraying citrus trees from a nutritional viewpoint. Proc. Fla. State Hort. Soc. 56: Fiskell, J. G. A., P. H. Everett and S. J. Locascio. Minor element release from organic-n fertilizer materials in laboratory and field trials. Jour. Agr. and Food Chem. (In Press) Haertl, E. J. and A. E. Martell. Metal chelates. Jour. Agr. and Food Chem 4: Heath, D. V. S. and J. E. Clark. Chelating agents as plant growth substances possible clue to the mode of action of auxin. Nature 177: Ibid. Chelating agents as growth substances. Nature 178: Shannon, L. M. and J. S. Mohl. Chelating agent effect on micronutrient balance in plants. Symposium on the use of metal chelates in plant nutrition, pp National Press, Palo Alto, Calif Sites, J. W. Present status of organic versus inorganic nitrogen as related to yield and fruit quality. Proc. Fla. State Hort. Soc. 62: Steenbjerg, F. Yield curves and chemical plant an alyses. Plant and Soil 3: Wallace, A. A decade of synthetic chelating agents in inorganic plant nutrition, pp A Wallace Ed. Edwards Brothers, Inc., Ann Arbor, Mich Wallace, A., L. M. Shannon, O. R. Lunt and R. L. Impey. Some aspects of the use of metal chelates as micronutrient fertilizer sources. Soil Sci. 84: Weinstein, L. H., A. N. Meiss, R. L. Uhler and E. R. Purvis. Growth promoting effects of ethylenediamine tetraacetic acid. Nature 178: THE RESPONSE OF OKRA TO NITROGEN, AND POTASSIUM FERTILIZATION PHOSPHORUS Paul Sutton Strawberry and Vegetable Field Laboratory Plant City The fertility requirements for okra are im portant in regard to early and total yields. In the spring, prices for the first okra harvested are generally higher than later when the supply is increased from other okra-producing areas. It is generally believed that high initial fertility will increase plant growth and decrease early okra yields. Eguchi et al (1) working with tomatoes, Florida Agricultural Experiment Stations Journal Series No eggplant and pepper in pot cultures, found that by increasing the rates of nitrogen, phosphorus and potassium the time of flowering was not de layed. However, when one or two of the elements were not applied the length of time required for flowering was increased. Ware (4) reported that phosphorus increased the total and early yields of snap beans. In a review of vegetable fertility studies pre viously conducted in Florida, no information was found on fertility studies with okra. Hester and Sheldon (2) reported that a combined weight of 11.5 tons (green weight) of pods, leaves and stems of okra contained 21, 10, 62 and 46 pounds