5o8 



Journal of Agricultural Research 



Vol. XII, No. 8 



Table I. — Percentage of humus to a depth of j feet in mulched basins in orange groves 

 on clay loam, soil. Experiment I 



Date. 



1915- 



Mar. 31 



Aug. 13 



Sept. 13 



Oct. 12 



Nov. II 



Nov. 20 



Dec. II 



Average for 191 s.* 



1916. 



Mar. 17 



Apr. 17 



May 15 



June 16 



July 13 



Ai»g. 7 



Average for 1916. . 

 Ratio 1916 to 1915 



Basin treatment and percentage of htunus. 



Large basins installed in March. 



Alfalfa 

 alone. 



3-075 

 •073 

 •075 

 .084 

 .098 

 .187 

 . iq8 



"3 



•113 

 . Ill 

 . 076 

 . 112 

 .081 

 .185 



113 



Manure 

 alone. 



118 

 130 

 136 



153 

 186 

 188 

 180 



.156 



201 

 246 



133 

 231 



295 

 292 



233 



1.49 



Alfalfa 

 and lime. 



D. 113 

 . 106 

 .147 

 •155 

 .185 

 .150 

 .188 



149 



180 

 287 

 ,181 

 288 

 272 

 215 



237 



1-59 



Manure 

 and lime. 



O. 129 

 . 112 



•139 

 . 160 



•151 

 •151 

 .156 



143 



179 

 213 

 141 

 220 

 207 

 227 



1.38 



Small basins in- 

 stalled in August. 



Alfalfa 

 alone. 



O. 166 

 . 114 



. 118 



130 



171 

 257 

 ^33 

 165 

 117 

 212 



176 



1-35 



Alfalfa 

 and lime. 



0.16s 

 . 092 

 . 108 



096 



"S 



259 



107 



139 



III 



175 



151 



I- 31 



It will be observed that the determinations show a fluctuation in the 

 percentage of humus from time to time. This is doubtless due partly 

 to the difficulty of getting uniform soil samples. This factor, however, 

 does not afford a complete explanation, because the same kind of fluc- 

 tuation was noted when determinations were made on soils kept in pots 

 in the laboratory, where better control conditions obtained and where 

 leaching was avoided. Neither can the fluctuations be due entirely to 

 the working error in making humus determinations, since these errors 

 are of smaller magnitude than the variations in the humus content of 

 the soils. 



The following duplicate determinations made on March 31, 1915, the 

 averages of which are given on the first line in Table I, illustrate the 

 working error in making humus determinations by the method employed 

 (Table II). 



Heinze (6) states that after humus has been formed other bacteria, 

 such as Azotobacter, commence to decompose it. McBeth (9) lays stress 

 on the fact that the cellulose destroying organisms in the soil break down 

 the organic matter in the soils with the formation of humus, and that the 

 nitrifying organisms break the humus up into still simpler compounds 

 through their nitrifying activities. 



