Mineral Nutrition Status of Valencia Orange


 (6). A Beckman Model DU Flamephotometer with hydrogen-
 oxygen flame and photo-multiplier was used for analysis of potas-
 sium and calcium. A compensating solution was used to elim-
 inate errors in the flame determination of calcium due to the pres-
 ence of interfering anions. The "Rapid 8-Quinolinol" method
 (30) was followed to measure magnesium.
 Soil Analysis.-Available phosphorus was extracted with a
 solution composed of 0.03 N sulfuric acid and 0.03 N ammonium
 fluoride, as proposed by Miller and Axley (8) with slight modifi-
 cation. A 10-gram soil sample was shaken with 50 ml. of the
 above extracting solution for 30 minutes and filtered through
 Whatman No. 42 paper. Phosphorus was then determined with
 the same method used for leaves and fruits. Extractable cal-
 cium and magnesium were extracted from the soil with sodium
 acetate solution having a pH of 4.8 and determined by methods
 described by Peech and English (10). Copper content of the
 soil was estimated with the rapid method described by Spencer
 (27). A Model M Beckman pH meter with glass electrode was
 used to measure the soil reaction.
 Fruit Quality.-External fruit quality was measured by three
 characteristics: color, texture and size. Rind color was expressed
 in percent of green fruit. Any fruit showing even a slight trace
 of green was classified arbitrarily as a green fruit. On this basis
 the percent of green fruit was high for most of the samples.
 Smoothness at stem end was used as an index to express the
 general texture of the rind. Each fruit was classified as being
 either rough or smooth, and the results were expressed as per-
 cent fruit smooth at stem end. Commercial packinghouse sizers
 were used to measure size and this was expressed in inches of
 diameter.
 To study internal fruit quality, juice was extracted by a
"F.M.C. In-Line" juice extractor, strained through a fine sieve
to remove fragments of albedo and other solid particles, and
weighed. The percentage concentration of soluble solids in the
juice was measured with Brix hydrometers corrected for tem-
perature. Acidity was titrated against standard sodium hy-
droxide, using a Beckman Model K automatic titrator. Vitamin
C (ascorbic acid) was measured by titration against a standard-
ized sodium 2,6-dichloroindophenol dye. The "ratio" (soluble
solid/titratable acid) and the "percentage juice by weight" are
calculated values.