26 BULLETIN 499, U. S. DEPARTMENT OF AGRICULTURE. 



HUMUS CONTENT OF THE BASINS AND THE CHECK SOILS. 



SUNNY MOUNTAIN GROVE. 



Determinations of the humus content of the soil in the basined 

 area and in the untreated area to a depth of X feet are given in Table 

 X. Determinations of humus are necessarily somewhat inaccurate, 

 owing not only to the variation in sampling but also to the fact that 

 humus, so-called, is an indefinite mixture of organic compounds. 1 

 The Sunny Mountain grove, so far as known, had been treated uni- 

 formly previous to the installation of the mulched basins. Composite 

 samples collected in 1914 indicated that the check area contained 

 slightly more humus than the basined area. In the spring of 1915, 

 however, the surface foot of the basined area was higher in humus, 

 as shown in Table XIII. The humus content of the surface foot of 

 soil below the mulch also increased gradually throughout the sum- 

 mer, while the check area, which received no organic material save 

 that contained in commercial fertilizers, showed practically no 

 change. The increase in humus in the basins is confined practically 

 to the first foot of soil. At lower depths the humus content of the 

 two tracts differs but slightly, decreasing gradually to a depth of 6 

 feet, as shown by the mean values in Table X. If the humus con- 

 tent of the soil is limited, it is advantageous to have it localized 

 largely in the upper 3 feet of soil, which in most California soils 

 includes the principal feeding roots of citrus trees. 



Table X, 



-Percentage of humus in the first and in the second 3 feet of soil in 

 the Sunny Mountain grove, California, in 1915. 





Basins near upper 

 end of tract. 



Basins near lower 

 end of tract. 



Av- 

 erage, 



Furrow system 



near upper end of 



tract. 



Furrow system 



near lower end of 



tract. 



Av- 

 erage, 



Depth and 











both 

 ends 









both 



date. 



+j 



ti |t) 



■ 



-w It! 



T) 



, 



i It) 



T) 



, 



+j I'd It) 



, 



ends 





tO *J 



fl p I. J 



*"* m 



w +i 1 a « 



fc..J 





of 



<n+s\a^ 



f-t 4jJ 





to jj d «■ 1 «- *» 



t- . 



of 





I- o 



— o 



o o i— < o 



go l.d.0 



? So 

 > C3 



K o o o 



S5 



k. b/o 



tract. 



fcc o o o 



.hO'JO 



s§ 



k, bo 



t. O O O — ' o 



>& 



tract. 





to 



TO 



H 





to 



TO 



H ' 



< 





to 



TO 



H " 



-^ 



to to Eh 



< 





First 3 feet: 



































-\pr. 9... 



0.52 



0.18 



0.17 



0.29 



0. 53 



0.34 



0.21 



0.36 



0.33 



0.37 



0.27 



0.13 



0.26 



0. 37 0. 27j0. 14 



0.26 



0.26 



June 15 . 



.63 



.22 



.13 



.33 



.59 



.29 



.13 



.34 



.33 



.32 



.24 



.11 



.22 



. 42 . 35 . 17 



.31 



.27 



July 10.. 



.72 



.26 



.10 



.36 



.63 



.25 



.16 



.35 



.35 



.42 



.18 



.10 



.23 



. 29 . 42 . 22 



.31 



.27 



Aug. 6.. 



.67 



.28 



.14 



.36 



.50 



.23 



.13 



.29 



.33 



.37 



.24 



.17 



.26 



. 50 . 44 . 18 



.37 



.32 



Sept. 21 . 



.84 



.16 



.08 



.36 



.67 



.36 



.10 



.37 



.37 



.36 



.20 



.11 



.22 



. 37 . 32 . 26 



.27 



.27 



Aver- 



































age.. 



.68 



.22 



.12 



.34 



.58 



.29 



.15 



.34 



.34 



.37 



.23 



.12 



.24 



. 39 . 36 . 19 



.30 



.28 



1 The humus was determined by removing the calcium with 1 per cent hydrochloric 

 acid, extracting with sodium hydroxid, and measuring the intensity of the humus color 

 against a standard humus solution in a colorimeter. The standard solution was freshly 

 made up by weight from uniform dry stock material obtained by extraction with 4 per 

 cent ammonia after treating with 1 per cent hydrochloric acid and washing free from 

 chlorids. The ammonia extract was filtered through a Pasteur-Chamberland filter before 

 evaporating to dryness. 



