MINERAL COMPOSITION OF CITRUS LEAVES FROM THE INDIAN RIVER AREA OF FLORIDA

Transcription

1 32 FLORIDA STATE HORTICULTURAL SOCIETY, 1952 MINERAL COMPOSITION OF CITRUS LEAVES FROM THE INDIAN RIVER AREA OF FLORIDA Herman J. Reitz and Wallace T. Long Florida Citrus Experiment Station Lake Alfred In the summer of 1952 a collection of 103 leaf samples was taken from citrus groves in the Indian River area of Florida. These were analyzed for the major elements ordinarily found in such leaves. This work was under taken for two reasons. First, data from com mercial groves were desired for comparison with data obtained from the Indian River Field Laboratory fertility plots. This would help in evaluating the fertility plots. Second, the survey was undertaken as a preliminary to the expansion of fertility work into areas outside St. Lucie County on a cooperative basis with growers. It was felt that a preliminary leaf analysis survey would make possible more intelligent selection of groves in which this work could be carried on and help to indicate the levels of various fertilizer elements which it would be desirable to include in such experiments. At the conclusion of the survey the actual data obtained seemed to be of some interest for comparison of the Indian River area with interior Florida and the Western States, and for discussion of some apparent trends. Methods Leaf samples were taken of Valencia oranges and seedless varieties of grapefruit. Most of the grapefruit-leaf samples were Marsh, but a small number of samples of pink and red varieties were also taken. Nearly all groves sampled were on sour orange rootstock. Samples were collected during July, August, and September, with the majority col lected during August. Each sample consisted of 100 leaves taken from 10 healthy trees. As nearly as could be determined, all leaves were of spring-flush growth, and from nonbearing shoots. After collection, leaf samples were washed thoroughly in a solution of a detergent, with tap water and deionized water, and dried at 70 C. Florida Agricultural Experiment Station, Journal Series No Nitrogen was determined by a semimicro Kjeldahl method. Magnesium was determined by the method of Wilson (13). Phosphorus was determined by the method of Peech et al. (8). Calcium, potassium and sodium were deter mined with a Perkin-Elmer flame photometer. Valencia Results Orange and Discussion Average analysis of the Valencia orange leaf samples are presented in Table 1, together with some of the data of Reuther et al. (10) for Texas, Arizona, and Central Florida, and Chap man's (2) data for high yielding orchards in California. It is readily apparent that citrus leaves from the Indian River area more close ly resemble in composition those of Texas, Arizona and California than leaves taken from Central Florida locations. Leaves from the Indian River area averaged lower in nitrogen, phosphorus, potassium and magnesium, but higher in sodium and calcium, than leaves from interior Florida. The differ ence in rootstock between the rough lemon groves of Central Florida and the sour orange groves of the Indian River area contributes to the difference in leaf composition found in the case of nitrogen, but the effect of rootstock should make the potassium higher and the cal cium lower in the Indian River samples (12). Calcium relationships. The wide range of calcium analyses found in the Indian River samples (Table 1) led to the opinion that cor relations should be found between calcium and the other elements. This expectation was based upon previous work (2,5) showing the effect of one element on absorption of another. Correlations were computed between calcium and the five other elements for which analyses were made. These correlations are presented in Table 2, together with a summary of the analytical values found. In order to condense the data, the samples were grouped into classes based on calcium content of the leaves. Each of these classes consists of all those samples in which the leaf analysis for calcium fell within a certain halfpercent calcium range. For example, all the

2 REITZ AND LONG: LEAF COMPOSITION 33 samples having between 4.01 and 4.50 percent calcium were grouped into a single calcium class, in which there were four samples. These samples were averaged and the averages for this and other similarly-created classes are pre sented in Table 2. As the calcium in the leaves increases, less potassium, phosphorus, nitrogen and magne sium is found in the leaves. The strength of the relation is measured by the size of the negative correlation coefficients given in Table 2. The conclusion is inescapable that mineral nutrition of citrus trees in the Indian River area is strongly influenced by soil conditions which govern the calcium in the leaves. The trends noted here are doubtless caused by a combination of soil factors. The leaf analyses merely show the net effect of these causal factors. When the data are arranged according to calcium composition, the low calcium classes are found to be very similar in analysis to the interior Florida leaves; while the high calcium classes are very similar in composition to leaves from the Western states. The data for Texas are very similar to the Indian River data for the calcium class 5.01 to 5.50, into which the Texas average would fall. The most significant discrepancy is in potassium, in which Texas samples run considerably lower. This is doubtless due to the non-use of potas sium fertilizers under Texas conditions. The ph of the surface soil was not closely related to the calcium status of the leaves. Surface soil samples were taken from each of the groves in which the leaves were sam pled, and ph of these soil samples was de termined (Table 2). A range in ph from 4.0 to 8.1 was obtained. The relation between the calcium found in the leaves and the ph of the surface soil was weak. Most of the leaf samples low in calcium came from groves with acid surface soils, but some of the high cal cium samples also came from groves with acid surface soils. The reason for this is not difficult to surmise; for it is common, if not most prevalent, for even acid surface soils in the Indian River area to have more alkaline or calcareous subsoils (9). The possibility exists that a classification of the data by calcium content is biased by dif ferent kinds of fertilizer used on high calcium and low calcium groves. That is, the groves on calcareous soil may receive one set of fer tilizer formulas and amounts, while those on acid soils may receive a different set. This would make the grouping on the basis of leaf calcium content untenable. This view was rejected for two reasons. A study of the fertilizer records of the specific groves studied indicated that fertilizer pro grams were generally similar on all soils. In die second place, it appeared that the most probable bias, if any, would be in the direc- Table 1. Summary of Valencia Orange Leaf Analyses from Five Producing Areas of the United States. Area Reference Source No. of Samples Analysis - Percent of Dry Weiffht Ca **- Indian River, Fla. Original a Interior Florida Reuther et al., (10) HI Texas Reuther et al., (10) Arizona Reuther et al., (10) S U California Chapman (ar"

3 34 FLORIDA STATE HORTICULTURAL SOCIETY, 1952 tion of higher potash on marl soils. If any bias exists, then, it should tend to deemphasize the trends under discussion. Since the ferti lizer practice seems fairly uniform, and since the most probable direction of any bias tends to counteract the calcium trends noted, it is believed that bias due to fertilizer practice can be largely disregarded, except as it pro duced considerable variation in the data. Potassium content of leaves was more strong ly correlated with calcium content than were any of tfre other elements. A very wide range of calcium and potassium values was found. Calcium ranged from 3.32 percent to.80 percent, while potassium ranged from 0.41 percent to 2.13 percent. Where calcium was low, potassium was relatively high, except in the case where little was added in the fertilizer. However, where calcium was high none of the values obtained for potassium was high. Some of the potassium values found were among the lowest recorded in the literature from samples taken in the field, and the lowest on record from Florida. Apparently on the light sandy coastal soils (similar to those of Central Florida), citrus trees find little diffi culty in absorbing potassium from available supplies, but apparently the conditions present in calcareous soils of the coastal regions make potassium absorption more difficult. It is difficult to believe that the wide range of potassium analysis found is essential to good fruit production, even under the variety of conditions found in the Indian River area. It would appear that either the high values were excessively high or that the low values were excessively low, or that soil conditions modify the citrus tree's requirement for potas sium. A point needs to be established which would represent the optimum level of potash. Table 2. Classification of Valencia Orange Leaf Samples Into Groups Based on Calcium Content. Range of Ca Analyses No. of In Group Ca Analysis - Percent of Dry Weight K Mg N P Na Range of Soil ph Less than B Over Correlation of other elements with calcium -.72** * -.412**.030 * Significant correlation at 55» level. ** Significant correlation at 1% level.

4 REITZ AND LONG: LEAF COMPOSITION 35 A search of the literature affords some frag ments of the solution. Several experiments have been run on acid sandy soils. One of the earliest of these was the experiment of Bahrt and Roy (1), in which a value of 0.87 percent potassium in the leaves was found in plots which had low yields of small, thin-rind, early maturing fruit low in acid and high in soluble solids, and 1.24 percent was given representing plots without these symptoms of potash deficiency. More recently Reuther and Smith (11) have shown that these fruit qualities can be affect ed by potash levels aeove 1.3 percent, the leaf samples being taken in July. Parker and Jones (7) in California concluded from an experiment on Ramona loam that fruit size was depressed by potash levels below 1.5 percent in leaves in August and September. In the present survey of 48 groves, 10 samples were found to be below the value given by Bahrt and Roy, 28 were below the value given by Reuther and Smith, and 37 were below the value given by Parker and Jones. It ap pears probable that fruit size, rind character, and possibly even yield are being influenced by potassium supply in some Indian River groves. It is probable that the higher potassium values reported here are undesirably high from the economic standpoint, since no benefit even on fruit size has been obtained in experi mental work by holding the potassium higher than about 1.5 percent (7). This would be particularly true with Valencias, which often grow larger than necessary to receive good acceptance in the markets. It would appear that several of the high potassium groves sam pled could be more economically operated on lower potash fertilization without change of yield, fruit size, or fruit quality. It is interesting to speculate that the high quality of Indian River fruit is due not only to the use of sour orange rootstock but also to the fact that throughout the area potash levels are generally low. It is of further sig nificance in this respect that the highest qual ity fruit is believed to come from soils which result in high calcium content of the leaves and low potassium. From the standpoint of effect on fruit qual ity, the low potash values are desirable up to the point at which the size is undesirably af fected, and premature dropping and possibly creasing effects may be important. The exact level at which these effects occur is not known under the conditions of the Indian River area. It probably cannot be determined with a high degree of precision, because of variation in crop size from year to year. All investigators agree that fruit size is one of the first characters to be affected by low ering potassium supplies (1,7,11). Unless some loss in fruit size can be tolerated, little overall benefit on fruit quality can be expected to result from decreasing the potassium level in groves producing for the fresh-fruit market. This would appear to be of most importance on early and midseason varieties of oranges in the southern part of the Indian River area, where small size of early and midseason oranges is not infrequently a problem. For processing purposes, more loss in fruit size can be tolerated, with possibly more economy in fertilizer cost. These considerations tend to support the view that the present average value of 1.15 percent for the Indian River area is not far above a minimum amount of potassium. Cer tainly the 15 groves found with potassium less than 1 percent would appear to be in a ques tionable potassium status. The fact cannot be ignored that the subtantial citrus industries of the Western states are based on potash levels less than found in the average Indian River grove, (Table 1), together with higher calcium levels. Some of these groves are apparently bearing satis factorily on potash levels lower than any re ported here. Chapman (2) analyzed leaves from groves having records of high production in California, and found one of the ten se lected with a potassium level of only 0.38 percent. Apparently satisfactory groves with potassium level approaching this value were found in this survey, but under calcareous soil conditions. On acid sands, no values as low have been reported. None of the Indian River groves showed potassium deficiency when sampled, but the symptoms would be expected to ap pear later than when the groves were visited in midsummer. Thus, there is some reason to believe that satisfactory levels of potassium in leaves may vary with other conditions, but the evidence is weak at this point. For the present, it appears necessary to apply more

5 3 FLORIDA STATE HORTICULTURAL SOCIETY, 1952 potash under calcareous soil conditions than would be necessary under acid soil conditions. Average leaf analyses for phosphorus are similar in all of the regions for which data are reported (Table 1). The average found for the Indian River samples is slightly lower than that reported for Central Florida. The negative correlation of calcium and phosphorus (Table 2) is statistically significant at the 1 percent level, but still of a low order, in dicating the importance of other factors in the uptake of phosphorus. The existence of the correlation is due mostly to the presence of low phosphorus values in leaves with cal cium over.0 percent. Below this level there is not much difference associated with cal cium. Two of the samples were found to analyze less than 0.10 percent phosphorus, which is the upper limit of the range suggested by Chapman for slight phosphorus deficiency (3). If any significance may be attached to these figures, it is that in the calcareous soils more attention must be paid to phosphorus fertiliza tion than under acid soil conditions. This con clusion was indicated by previous studies of phosphorus availability (). Nitrogen was inversely related to calcium, as noted above. The danger of correlation by coincidence is always present, but data from Experiment 5 at the Indian River Field Lab oratory reinforces the belief that the correla tion is of some significance. In this case iden tical fertilizers are applied to two soils of dif ferent calcium characteristics, and nitrogen runs higher where calcium is lower, and vice versa. The significance of the nitrogen-calcium re lation is in doubt at present. Few of the groves sampled showed symptoms in the leaves of nitrogen deficiency. Where leaf symptoms of nitrogen deficiency were intentionally de veloped at the Indian River Field Laboratory, leaf analysis in midsummer indicated levels of 1. to 1.8 percent. The transitory nature of nitrogen level in leaves makes it difficult to Table 3. Classification of Seedless Grapefruit Leaf Samples into Groups Based on Calcium Content. Range of Ca Analyses No. of In Group Ca Analysis - Percent of Dry Weight K Mg N P Na Range of Soil ph Less than 3.O5C OI-.5 More than.50 All Samples Correlation of other elements with calcium * &T * !o * % 1.33.&L * ** % » ** A ** * Significant correlation at 5% level. * Significant correlation at 1% level.

6 REITZ AND LONG: LEAF COMPOSITION 37 establish any significant level of nitrogen as sociated with any yield or fruit quality char acteristic. Such information would be very valuable in the case of an element of such importance to fruit production as nitrogen. The correlation between magnesium and calcium was surprisingly low in view of the significant calcium-potassium relationship. The poor relationship may be due to the generally high magnesium analysis. High analytical val ues for magnesium were obtained at both high and low calcium levels. It is suggested that magnesium is better able to compete with calcium in absorption processes than is potas sium or that magnesium in the soil is currently in better supply relative to requirements than is potassium. In the field under some condi tions, magnesium deficiency has been very persistent and has presented a definite prob lem. On the other hand some experimental plots at the Indian River Field Laboratory have surprisingly failed to show magnesium deficiency under very limited supplies. Much remains to be learned about this element un der field conditions. Sodium was not found to be correlated with the calcium content of leaves. This is not surprising in view of the fact that much of the sodium found in Florida citrus groves apparently reaches the grove through either salt water intrusion, application of salty irriga tion water, or as mist or spray carried from the ocean by winds. Hence the occurrence of sodium in the leaves would appear to be more closely related to the location of the grove than to the character of the soil or to fertilizer practices. Evidence that this is true is found in the fact that four of the five high est sodium values found were from one of the coastal islands, where all three of the sodium sources named above could well contribute to the total. Values much higher than those re ported here have been found in some samples taken from these areas during the winter months. Average sodium values given are higher than found in other regions. Marsh and other Seedless Varieties of Grape fruit A summary of the results of analysis of 0 samples of seedless grapefruit leaves is pre sented in Table 3. This table parallels in form Table 2. Little data from other areas are available for comparison. In comparison with oranges, the grapefruit samples average lower in nitrogen and slight ly lower in calcium and sodium. On the other hand, the grapefruit samples average higher in potassium than the orange samples, and somewhat higher in magnesium. The most significant differences are in nitrogen and po tassium. It is not known whether these dif ferences are due to location of the groves from which samples were taken, or whether they represent real differences due to the scion varieties. There is some supporting evidence that the potassium tendency is a characteristic scion effect (4), but the situa tion in regard to nitrogen is not known. The negative correlations of the other ele ments with calcium were also found in the grapefruit samples. In general the correlation coefficients (Table 3) were somewhat more highly significant statistically than found in the orange samples, because of their greater magnitude and also because of the greater number of pairs of values used in their com putation. A notable exception to this was potassium, where the coefficient was consid erably smaller than for oranges. This fur ther supports the opinion that the higher po tassium levels in the grapefruit leaves is char acteristic of the scion. Unless the fertility practices include higher applications of potash on grapefruit (a possibility not supported by the authors' observations) it appears that the grapefruit is able to obsorb potassium more easily than does the orange. Presumably the differences in nitrogen and potassium absorp tion by orange and grapefruit hold forth a possibility for the development of different fertilizer practices for orange and grapefruit groves, but this possibility remains unexplored. Summary Leaf samples were taken from 43 Valencia orange groves and 0 seedless grapefruit groves in the Indian River Area of Florida, and analyzed for six major elements. Citrus leaves from the Indian River Area more closely resemble in composition leaves from the West ern States than those from Interior Florida. Indian River Valencia leaves are lower in nitrogen and potassium but higher in calcium and sodium than Interior Florida samples. Negative correlations were found between leaf

7 38 FLORIDA STATE HORTICULTURAL SOCIETY, 1952 calcium content and leaf content of potassium, phosphorus, nitrogen, and magnesium, in both Valencia orange and seedless grapefruit sam ples. Grapefruit leaf samples were higher in potassium and lower in nitrogen than Va lencia orange leaf samples. Practical appli cation of this information is discussed. LITERATURE CITED 1. Bahrt, G. M.. and W. R. Roy. Progress Report of the effects of no potassium and various sources and amounts of potassium on citrus. Proc. Fla. State Hort. Soc. 53: Chapman, H. D. Tentative leaf analysis stand ards. Calif. Citrog. 34: Chapman, H. D., and D. S. Rayner. Effect of phosphorus deficiency on orange trees: appear ance, and fruit quality. Citrus Leaves 31: Cooper, W. C, B. S. Gorton, and E. O. Olson. Ionic accumulation in citrus as influenced by rootstock and scion, and concentration of salts and boron in the substrate. Plant Physio. 27: Fudge, B. R. The effect of application of cal cium and magnesium upon absorption of po tassium by citrus. Proc. Fla. State Hort. Soc. 59: McGeorge, W. T. Factors influencing the avail ability of native soil phosphate and phosphate fertilizers in Arizona soils. Ariz. Agr. Expt. Sta. Tech. Bull. 82: Parker, E. R., and W. W. Jones. Effects of fertilizers upon the yields, size and quality of orange fruits. Calif. Agr. Expt. Sta. Bull. 722: Peech, Michael, L. T. Alexander, L. A. Dean, J. Fielding Reed. Methods of soil analysis for soil fertility investigations. U. S. D. A. Circular No. 757: Peech, Michael, and T. W. Young. Chemical studies on soils from Florida citrus groves. Fla. Agr. Expt. Sta. Bull. 448: Reuther, Walter, Paul F. Smith, and Alston W. Specht. A comparison of the mineral composi tion of Valencia orange leaves from the major producing areas of the United States. Proc. Fla. State Hort. Soc. 2: Reuther, Walter, and Paul F. Smith. The rela tion of nitrogen, potassium and magnesium fertilization to yield, leaf composition, and the incidence of zinc deficiency in oranges. Proc. Amer. Soc. for Hort. Sci. 5: Smith, Paul P., Walter Reuther, and Alston W. Specht. The influence of rootstock or the min eral composition of Valencia orange leaves. Proc. Fla. State Hort. Soc. 1: Willson, A. E. Rapid 8-quinolinol procedures for determination of magnesium. Analytical Chemistry 23: EFFECT OF COPPER AND LEAD ARSENATE SPRAYS ON THE TOTAL ACID AND MATURITY OF DUNCAN GRAPEFRUIT E. J. Deszyck, H. J. Reitz, and J. W. Sites Florida Citrus Experiment Station Lake Alfred The use of copper compounds in the pro duction of high quality citrus fruit as fungicidal and physiological sprays and as com ponents in the fertilizer is a general practice in Florida. It has been observed frequently that grapefruit trees sprayed with copper sprays matured fruit a little later than fruit from unsprayed trees. This delay in matur ity has resulted when copper sprays are used either as a fungicide applied at the postbloom period, or as a physiological spray ap plied to dormant trees. Examination of the grapefruit from copper-sprayed trees showed that a higher total titratable acid content was responsible for the delay in maturity. Fudge and Fehmerling (3) and Cowart and Steams (2) presented data showing the Florida Agricultural Experiment Station Journal Se ries No effect of copper fertilizers and sprays used in combinations with other elements on the acid and on the soluble solids to acid ratio in oranges and grapefruit. These authors re ported no significant changes in the acid or the ratio values. Marloth and Stofberg (5) working in Africa found no effect of cop per carbonate on the total acid of Valencia oranges. Reitz () found that an increase in the acid, and consequently a delay in ma turity, of Duncan grapefruit resulted from a copper spray application followed by lead arsenate. Camp and Fudge (1) reported that a copper deficiency of oranges resulted in low acid fruit. The purpose of this paper is to show the effect of copper sprays on the titratable acid content and on the maturity of Duncan grape fruit. Since lead arsenate sprays are used on grapefruit to reduce acidity and thus promote earliness of maturity, it is also of interest to the grower to know the effect of copper sprays when used in conjunction with lead arsenate.