73Q 



Journal of Agricultural Research 



Vol. VI, No. 19 



The results of the analyses of orange soils, together with the percent- 

 age of mottled leaves in each grove, are presented in Table I. In all 

 cases, unless otherwise stated, the soil data given represent a sample 3 

 feet in depth. Each foot section to a depth of 3 feet was analyzed sepa- 

 rately, but the results of the determinations on the individual foot sec- 

 tions disclose no relationships that are not equally well represented by 

 the mean value. The analytical data from the orange groves were 

 first considered in relation to soil type. While the soils around Redlands, 

 Highlands, and Riverside differ to some extent in their physical charac- 

 teristics, no correlation between mottle-leaf and soil type was in evidence. 

 Furthermore, the fact that mottling seems to be about equally advanced 

 on all the soil types of this area, other conditions, as age of grove, general 

 treatment, etc., being the same, would indicate prima facie that the soil 

 type is by no means a controlling factor. The results obtained from all 

 the orange groves studied in the districts around Riverside, Redlands, 

 Highland, and Rial to are therefore presented collectively. A few groves 

 studied around Pomona, Ontario, and Azusa are not included in this 

 grouping, since the soil conditions of these districts are quite different, 

 in so far at least as the organic content is concerned. 



To facilitate further comparison, the orange-grove data are grouped 

 in Table II on the basis of the percentage of mottling. Each group rep- 

 resents the average of about 20 groves, so that each point on the accom- 

 panying graphs represents an average of about 60 separate determina- 

 tions of a given factor, and approximately 200 mottling determinations. 1 

 The fact that mottling is not dependent upon the texture of the soil is 

 again emphasized in this table, which shows that the moisture retentive- 

 ness of the several groups as measured by the moisture equivalent 2 is 

 very nearly the same. 



Table II. — Analysis of orange-grove soils near Riverside, Redlands, Highland, and 

 Rialto, Cal., grouped according to percentage of mottled leaves, each group containing 

 approximately 20 groves 



Group. 



Percentage of — 



Total 

 nitro- 

 gen. 



Organic 

 carbon. 



Mineral 

 carbon- 

 ates. 



Mineral 

 bicar- 

 bon- 



ates. 



Ratio of- 



Humus 



to 



lime. 



Carbon 



to 

 humus. 



Nitro- 

 gen to 

 humus. 



Nitro- 

 gen to 

 carbon 



Moisture 

 equiva- 

 lent. 



Mot- 

 tled 

 leaves. 



.119 



. 142 

 . 170 

 .165 

 ■ 244 

 . 204 



0.036 

 .036 

 •039 

 •039 

 •039 

 ■ 038 



3-237 



.256 



.254 



•255 

 . 261 

 • 263 



0.069 

 .066 

 •093 

 .080 

 .068 

 •079 



0.023 

 .024 

 .026 

 .027 

 .020 

 .028 



3-303 

 •254 

 .229 

 •237 

 .159 

 .1S6 



o. 152 



.141 



.154 

 •153 

 • 149 

 .144 



Per cent. 

 3 

 4 

 6 

 6 



Percent. 

 88 

 64 

 43 

 19 



1 The ratios in Tables II and IV are calculated from the mean values of the measured factors. 



2 The moisture equivalent is a measure of the moisture retentiveness of a soil, and is numerically equal 

 to the percentage of moisture which a given soil is able to retain in opposition to a centrifugal force 1,000 

 times that of gravity. The finer the soil particles the greater is the moisture equivalent. 



