Aug. 7, 1916 



Mottle-Leaf of Citrus Trees 



735 



/oo 



eo 



soil can properly humify organic matter, the latter will apparently go 

 through the decomposition stages most beneficial to the growth of the 

 tree. 



NITROGEN CONTENT AND MOTTUNG 



The total nitrogen content in the soil was surprisingly uniform re- 

 gardless of grove conditions and soil types. The variation in total 

 nitrogen within the limits found in the soils of the groves examined 

 appears to bear no relation to the percentage of mottling (correlation co- 

 efficient = —0.02 ±0.06). A part of the nitrogen is undoubtedly held 

 in a form not imme- 

 diately available to 

 the tree and in this 

 respect is somewhat 

 analogous to the to- 

 tal organic carbon in 

 the soil. When the 

 orange soils are 

 grouped on the basis 

 of mottling, as in 

 Table II, the two most 

 badly mottled groups 

 show the lowest aver- 

 age nitrogen content, 

 but the differences are 

 so small as to have 

 little significance. 

 The other groups will 

 be seen from Table II 

 to have practically the same average nitrogen content. Such relation- 

 ship as exists may be due to the fact that part of the total nitrogen is 

 combined as "humus," so that the low humus soils would be lower in 

 nitrogen. 1 



«?o 



eo 



/ 2 



7~0 Z/A/2T //V sSO/Z- 



Fig. 3. — Graphical presentation of the relationship between the ratio 

 of humus to lime in the soil and the percentage of mottled leaves 

 (from data in Table II). 



LEMON SOILS 



The field studies of the lemon groves were carried on in a manner 

 similar to that of the orange groves. The lemon groves selected all 

 belong to the same company and constitute the principal lemon groves 

 in the Riverside district. The data for the individual groves are 

 presented in Table III and are grouped on the basis of mottling in 

 Table IV. 



1 For data regarding the nitrate content of the soils of the Riverside area, sec Kellerman, K. F., and 

 Wright, R. C. Relation of bacterial transformations of soil nitrogen to nutrition of citrous plants. In 

 Jour. Agr. Research, v. 2, no. 2, p. ici-113, 7 fig. 1914. 



