JOffiW OF MttHM RESEARCH 
Vol. IX Washington, D. C., May 21, 1917 No. 8 
EFFECT OF DECOMPOSING ORGANIC MATTER ON THE 
SOLUBILITY OF certain INORGANIC CONSTITUENTS 
OF THE SOIL 
By Charles A Jensen, 
Assistant in Plant Malnutrition Office of Biophysical Investigations , Bureau of Plant 
Industry , United States Department of Agriculture 
INTRODUCTION 
In an investigation already reported 1 relative to the cause of mottle- 
leaf of Citrus trees in southern California, it was found that the per¬ 
centage of mottling was inversely correlated with the humus content of 
the soil as measured by the amount of organic material extracted from 
the soil with a 4 per cent ammonium-hydrate solution, the calcium having 
previously been removed with hydrochloric acid. The examination of 
120 orange groves in the Riverside, Cal., district showed a correlation of 
0.67 between the mottling of the grange leaves and the reciprocal of the 
humus content in the soil. This association is further supported by the 
marked growth response of orange trees, especially on the clay-loam type 
in the district mentioned when irrigation water is supplied through basins 
mulched with organic material, the soluble organic products of the de¬ 
composition in the mulch being carried directly to the root system by 
the irrigation water. 2 
The marked growth response of Citrus trees following the addition of 
certain kinds of organic matter or of organic solutions derived from the 
decomposition of organic matter may be due to the addition of some 
organic or inorganic constituent, or possibly to some indirect action of 
the organic solution on the soil or the soil flora. The fact that chlorosis 
is sometimes associated with a deficiency of soluble iron, and that mag¬ 
nesium, according to the investigations of Willstatter 3 and his colleagues, 
is an essential constituent of chlorophyll, has made it appear desirable 
to determine if possible to what extent the addition of organic matter to 
the soil increases the solubility of these elements and other essential 
1 Briggs, L. J., Jensen, C. A, McLane, J. W. Mottle-leaf of Citrus trees in relation to soil conditions. 
In Jour. Agr. Research, v. 6, no. 19, p. 721-729. 1916. 
2 Briggs, L. J., Jensen, C. A, Me Lane, J. W. The mulched-basin system of irrigated Citrus culture 
and its bearing on the control of mottle-leaf. U. S. Dept. Agr. Bui. 499, 31 p., pi. 1. 1916. 
8 Willstatter, R. The chemistry of chlorophyll. In Rpt. 79th Meeting Brit. Assoc. Adv. Sci., 1909, 
p. 667-668. 1910. 
Journal of Agricultural Research, 
Washington, I). C. 
Vol. IX, No. S 
May 21, 1917 
