HUMUS IN MULCHED BASINS, RELATION OF HUMUS 

 CONTENT TO ORANGE PRODUCTION, AND EFFECT 

 OF MULCHES ON ORANGE PRODUCTION 



By Charles A Jensen, 



Assistant in Plant Malnutrition, Office of Biophysical Investigations, Bureau of Plant 



Industry, United States Department of Agriculture 



INTRODUCTION 



The formation of humus in a soil and its consen^ation are points that 

 are usually given much weight in discussions of soil fertility. The free 

 formation of humus in a soil from organic matter added to it is usiially 

 held to indicate that the soil its biologically active, and proper biological 

 activity in a soil is conceded to be necessary under the usual agricul- 

 tural practices. Hence, whatever the absolute value of soil humus may 

 be as a factor in crop production, it is ordinarily conceded, other fac- 

 tors being equal, that a soil which readily forms humus when organic 

 matter is added is superior to one that does not. 



Previous work (j)^ by this Office in southern California has shown 

 that the mottling of Citrus leaves varied inversely with the humus con- 

 tent in the soil. In other work by the same writers (2) it was shown 

 that on certain soil types in the general region of Riverside, California, 

 the use of the mulched-basin system in Citrus groves improved the tree 

 conditions more than the usual system of cultivation and furrow irriga- 

 tion, and that different green-manure substances when used as a mulch 

 affected tree growth and fruit setting in varying degrees. 



It is therefore of practical value to obtain information about the rate 

 of humus formation from various organic substances when employed 

 either as a mulch or when worked into the soil, and to ascertain, if pos- 

 sible, whether the increase in humus is correlated with increase in tree 

 growth and fruit setting. 



This work reports the study of humus formation in mulched basins in 

 Citrus groves, and the effect of different mulching materials on fruit 

 production and tree growth. The work was done at Riverside. 



The term "humus" as used in this paper is the brown-colored organic 

 matter extracted from a soil by boiling it for two minutes in a 7.5 per cent 

 sodium-hydrate solution, after the removal of calcium from the soil with 

 I per cent hydrochloric acid. 



The percentage of humus was determined colorimetrically by com- 

 paring the intensity of the color of the soil extract thus obtained with the 

 intensity of a standard humus solution prepared from the humus ex- 



' Reference is made by number (italic) to " Literature cited, " pp. sij~si& 



Journal of Agricultural Research, Vol. XII, No. 8 



Washington, D. C Feb. 75, 191S 



md Key No. G136 



(S05) 



