KUYKENDALL: IRON DEFICIENCY permanently in July 95 and the water level in the ditch was lowered seven and onehalf feet. The water table at the 0 foot position was lowered from 0 inches (June 95) 66 inches as measured in September 95. Root distribution will be studied in July 955 note any changes that may occur with a lower water table. Summary. Stabilizing the water table at a lower level increased the tal rooting area and the newly developed roots survived without peri odic destruction.. Lowering the water table from 0 70 inches doubled the quantity of feeder roots in four years and increased the size of the trees.. The feeder-root concentration in the deep-rooting zone (0-70") was greater than in the 0-0 inch zone and considerably higher than is usual for trees growing on deep, well drained sands.. When root distribution was above grams (expressed as dried feeder roots in a sq. ft. column) a visible increase in tree size could be noted. LITERATURE CITED. Ford, Harry W. 95. The effect of spreading decline on the root distribution of citrus. Proc. Fla. State Hort. Soc. 65: 7-50.. Ford, Harry W. 95. Unpublished data, Fla. Citrus Exp. Sta. SURVEY OF IRON DEFICIENCY IN FLORIDA CITRUS J. Richard Kuykendall* Florida Citrus Experiment Station Lake Alfred Iron deficiency is widespread in Florida cit rus, resulting in the well known yellowing or iron chlorosis pattern of the foliage. In recent years chelated iron has been used rather exten sively for the correction of this chlorosis. This has raised the question as the geographical and varietal distribution of iron deficiencies in citrus trees in the state. In order obtain some answers this question, a survey was made determine the relative leaf-iron con tent of various varieties of citrus in all of the major citrus growing areas of Florida. Leaf samples were collected from groves, representing all of the major commer cial varieties and all the major citrus growing districts of the state. One hundred and six teen of these groves are used in connection with the weekly insect and disease summary project of the Citrus Experiment Station. Rec ords are available on each of these groves, giving the location, rootsck, soil type, and fertilizer and spray applications for the past five years. The groves used for the insect and disease summary work were carefully selected Florida Agricultural Experiment Station Journal Series, No. 05. * Now with Geigy Agricultural Chemicals, Research Laborary, Bayonne, N. J. The work reported was conducted while the author was a member of the Flor ida Citrus Experiment Station staff and was aided by a grant from the Geigy Chemical Corporation. as being representative of the particular vari ety in the particular location. Sampling The leaf sample taken from each grove in cluded a random selection of 0 non-chlorotic leaves, summer flush 95, from each of the 5 trees, making a tal sample of 00 leaves. The leaves were from 5 6 months old at the time of sampling. Iron determinations and chlorophyll extractions were made on each sample of leaf material. No correlation could be established between iron and chlorophyll in these samples of green leaves and only the iron analysis will be presented in this paper. Iron Analysis All leaf samples be used for iron determi nations were washed by scrubbing with a soft nylon brush in a detergent solution, rinsed once in tap water and twice in deionized water. Washed leaves were dried in a forced air drier at 70 C. for 8 hours or longer, and then ground in a stainless steel Wiley mill, and sred in airtight glass jars. Dried leaf tissue was digested in 00 ml. volumetric flasks, using.00 gram samples and ml. of a 5: nitric-perchloric acid mix. Fol lowing digestion the solutions were allowed cool room temperature, then made up volume with deionized water. Solutions were then thoroughly mixed and allowed stand overnight allow the silica residue settle out on the botm of the flasks. Aliquots for iron determinations were taken from the p of
FLORIDA STATE HORTICULTURAL SOCIETY, 95 Location of Groves Sampled for Leof iron Survey Leaf Iron Content - Below 60 ppm - lew 60 90 ppm- Medium Above 90 ppm- High Fig.. Location of Groves Sampled for Leaf-Iron Survey.
KUYKENDALL: IRON DEFICIENCY 5 the solutions in such a way as not disturb the silica residue. Iron determinations were made using the ortho-phenanthroline proce dure. Results In order evaluate the data obtained from this survey, it was necessary establish cer tain leaf iron standards. Preliminary studies at the Citrus Experiment Station had estab lished that citrus leaves containing below 60 of iron may be chlorotic on trees growing on acid soil. On this basis the survey data was divided in three categories; below 60 of iron was considered as being low, between 60 and 90 of iron as medium, and any values above 90 iron were classified as high. A map showing the locations of the various groves and their relative leaf iron con tent (low, medium or high) is presented as Fig., and the data for iron analysis are in Tables, and. When all the information was evaluated, the mean leaf-iron content for all varieties in Efftct Table of Location and Rootack on leaf Iron Content of Citrus All varieties in all locations t All varieties: Axsft Upper East Coast Ridg Vest Coast All varieties in all locations: Rough leaon Number of Groves 7 5 5 0 0 6 5 Iron Content D~ 7. 60. 67.5 5.9 5. 65. 7.6 85.9 70.0 6. Range of leaf iron content vu from 5.0.0 Fe. all locations was found be 66.6 (Table ). Fifty of the groves, or 0.7 percent, had a leaf-iron content below 60 pprn. (Table ). This suggests that a much larger number of groves than was originally thought may have iron deficiency. In many of these in stances, iron chlorosis patterns may appear only at certain times of the year, such as dur ing growth flush periods. However, even in these cases the lack of sufficient iron could be one of the limiting facrs in the amount of growth produced. Trees containing the highest amount of iron were found in the, and districts, while trees from the In dian River and districts contained the least (Table ). The district trees contained on the average.5 more iron than those from the district The low values for trees in the and Upper East Coast areas was anticipated be cause of the calcareous nature of the soils on which the trees grow. In general, iron is not readily taken up by trees growing on calcare ous soils. There are, however, some indica tions from other work which is being done at the Citrus Experiment Station that citrus trees growing on these soils may have a lower iron requirement than trees growing on acid soils. Separation of the data according rootscks (Table ) shows that on the average, trees on rough lemon rootscks tended have higher leaf iron values than trees on sour orange rootscks. This was anticipated be cause of the more vigorous growth of trees on rough lemon rootsck, and because many of the groves on sour orange rootsck are on cal careous soil. The effect of rootsck on leaf iron content may be partially responsible for the very low iron values of groves in the In dian River (average 5. Fe) and Up per East Coast (average 60. Fe), where 5 out of 8 groves, or 8 percent, were on sour orange rootsck. This is contrasted with the data for the district (average 7.6 Fe) where out of 5 groves, or 96 percent, were on rough lemon sck. A separation of the data according varie ties (Table ) indicates a possible difference between varieties in their ability take up, sre and utilize iron. Valencia orange trees had the highest average iron content (7.6 ), with leaf iron values for Hamlin (66.8 ), and Parson Brown (65.6 ) trees being near the average for all varieties, and leaves of Pineapple orange trees being quite
6 Table Effect of Varieties on the Iron Content of Citrus Leaves Variety Area Number of Groves Iron Rootsck Number of Groves on Rootsck Iron (Rootsck) Valencia orange Upper East Coast 9 5 7, 58. 5. 75.6 76.5 7.9 85. Ave. 7.6 0 U 7.5 68.5 Hamlin orange 6 6 75. 7.8 8.9 57.5 58, 6..0 0 Ave. 66*8 5 69. - 59.6 Parson Brown orange J 7. 5.9 80.0 6.8 56. Ave. 65.6 7 65. 65.7 Pineapple orange Upper East Coast 57.5 5. 5. 5.5 89. 56. Ave. 59. 5 9 69. 5. Duncan grapefruit J> 0 7.5 5.5 5*. 5 7.7 Ave. 66.6 8 70..5 Marsh grapefruit _ 75.0 5.0 88.7 80.0 78. 9 69. 65. Ave. 70.8 Pink grapefruit (all varieties) AH locations 8 Ave. 67.9 Temple orange ««Ave..8 Dancy tangerine M " Ave. 6.9 Miscellaneous oranges n " 5 Ave. 6.
KUYKENDALL: IRON DEFICIENCY 7 low in iron, (59. ). The iron content of the other varieties of citrus was near or slightly higher than the over-all average, with the exception of the very low average for Temple oranges (.8 Fe). Summary A survey was made determine the iron content of citrus leaves from groves through out Florida. Leaf samples were collected from groves in counties, representing all of the major citrus growing areas. The mean leaf iron content for all varieties in all locations was found be 66.6 Fifty of the groves, or percent, had a leaf iron content below 60 Sixty-four groves on rough lemon rootsck (all varieties in all lo cations) had a mean leaf iron content of 70, while 5 groves on sour orange rootsck had a mean leaf iron content of 6 Pineapple orange groves (59 iron) and groves of Temple orange ( iron) and Dancy tangerines (6 iron) were low in leaf iron content compared with the state Table Range in Iron Content of Leaves of Various Varieties of Citrus in All Major Citrus Growing Areas of Florida Percent of tal number of groves with leaf iron content falling ^i l f o^-owittff r^nffes. Variety Fe Below 0 0 9 50 59 60 69 70 79 80 89 Above 90 Below 60 All varieties () 66.6.6 (7).9 (D 5. (5) 0. (0) 6. (). (). (50) 0.7 Valencia (5) 7.6 (5). (6) 7. (7) 0.0 (5). (5). (7) 0.0 (). Hamlin (0) 66.8 0.0 () 5.0 (6) 0.0 () 0.0 () 0.0 () 5.0 0.0 (9) 5.0 Parson Brown (n) 65.6 () 9. () 7. 8. 8. () 7. () 6. Pineapple (5) 59. () 6.7 (9) 60.0 () 0.0 () 6.7 () 6.7 (0) 67.0 Duncan (0) 66.6 () 0.0 0.0 0.0 () 0.0 0.0 () 0.0 Marsh () 70.8 5. () 7.7 5. () 0.8 5. 5. (). Numbers in brackets are number of groves with leaf iron content falling within each range* Includes varieties in addition the six listed.
8 FLORIDA STATE HORTICULTURAL SOCIETY, 95 average for all varieties in all locations. All of the other varieties on the average had a leaf iron content which was very close or above Upper East Coast and districts in general were below the state average. The low values for the and Upper the over-all state average of 66.6 Leaf East Coast areas were anticipated because of iron contents of groves in the, the alkaline nature of the soils in those areas. THE EFFECT OF LEAD ARSENATE SPRAYS ON QUALITY AND MATURITY OF RUBY RED GRAPEFRUIT E. J. Deszyck and J. W. Sites Florida Citrus Experiment Station Lake Alfred Since Ruby Red grapefruit is grown for the fresh fruit market, it is desirable know the seasonal changes in internal quality as related maturity. Fruit quality of grapefruit is in fluenced by acidity, soluble solids, ratio of solids acid, juice.content, and other facrs. These facrs form the basis for the legal ma turity standards defined by the Florida Citrus Code of 99. Very little is known about the seasonal changes in quality of Ruby Red grapefruit () although such information is available for Marsh and Duncan varieties (). In these white varieties, the solids content, ratio, and juice increase with maturity within certain limits, but the acidity and vitamin C gradually diminish as the season advances. In Florida, grapefruit trees sprayed with moderate amounts of lead arsenate (7) pro duce fruit of early legal maturity. Low amounts applied trees produce sweeter and more palatable grapefruit of high quality dur ing the remainder of the fruit season (6). Ar senic reduces the acid content of grapefruit by an unknown physiological process, thereby increases the ratio, and may advance legal maturity by as much as four months (). Variations in ratio between the unsprayed and sprayed fruit is generally small in the imma ture fruit, and large in the mature fruit- late in the season. For practical purposes, spray ing Marsh or Duncan grapefruit with lead arsenate does not influence the content of juice, vitamin C, or soluble solids in the fruit. Grapefruit sprayed with high concentrations of lead arsenate usually attains a slightly earlier maturity than fruit sprayed with mod- Florida Agricultural Series, No. 7. Experiment Station Journal erate amounts; however, the increase in the ratio is not proportional the rate in the spray. For example, a high rate of lead arse nate ( lb. per 00 gal.) applied Marsh grapefruit () increased the ratio approxi mately percent above that of the moderate rate. High rates not only cost more but there is also the possibility of tree injury and gum ming of the fruit, as a result of o much arsenic. From the standpoint of attainment of early maturity of grapefruit, a single spray of the moderate rate applied postbloom, or at any time before the average fruit diameter is ap proximately J inches (7,8) is usually most effective. Spraying grapefruit at any other time may not result in early maturity. Some growers believe that trees sprayed shortly be fore harvest produce mature fruit earlier, al though there is no evidence this effect. The purpose of this paper is show the seasonal changes in Ruby Red grapefruit qual ity with maturity. Although it is known that lead arsenate sprays hasten maturity, it is not known what extent various concentrations influence maturity and quality of the red grapefruit. Results of the past three seasons show that Ruby Red grapefruit is very re sponsive arsenic sprays, and that a lead arsenate spray at 0.8 lb./loo gal. was highly satisfacry in the production of early passing legal maturity ratios in the juice. Experimental A lead arsenate spray experiment was con ducted during 95-5, 95-5, and 95-5 on eight- ten-year-old Ruby Red grapefruit trees growing on sour orange rootsck in a commercial grove on Lakeland sand. The grove received complete fertilizer, cultural treatments, and the regular sprays with the exception of lead arsenate. Spray treatments