Feb. 25, 1918 



Humus in Mulched Basins 



511 



The basins with alfalfa as the mulch were the only ones which increased 

 in percentage of humus during the interval given. Other experiments 

 have shown that bean straw readily humifies. It is possible that if this 

 had been applied in as large a quantity as the other substances, these 

 basins would have increased in humus also. The lime was not consistent 

 in its effect on the amount of humus formed. 



It is to be noted, however, that the percentage of humus as found in 

 the summer, after the application of the mulches in the preceding fall, 

 does not necessarily indicate that in most of these basins the average 

 amount of humus had actually decreased. As shown in Tables I and III, 

 there are periodical fluctuations in the humus content, and the second set 

 of determinations shown in Table IV may have been made at a time when 

 the amount of humus was comparatively small. The figures in Table IV 

 probably give an indication of the relative humifying activity in the 

 basins. Each percentage given is an average of about six determinations. 



Experiment IV. — A series of basins was installed in a lemon grove 

 near Corona, Cal., in October, 1915. The soil is sandy loam in texture 

 interspersed freely with gravel so that samples below 3 feet can not be 

 taken with the ordinary soil tube. 



The mulching materials used were alfalfa and manure and, in addition 

 to the organic mulch, some of the basins received other artificial ma- 

 terials — ^viz, blood, phosphate, tankage, sulphur, bone meal, and lime. 

 In addition to the basined rows, several control rows were retained, and 

 were manured, irrigated, and cultivated in the usual way. The amount 

 of manure applied to the trees in the control rows was the same as appUed 

 in the basins. 



Soil samples were collected after the basins were made, on October 20, 

 1915, and another set was taken on June 29, 1916. The detailed humus 

 determinations made on the latter date did not indicate that any of the 

 artificial substances added to the mulches produced any definite influence 

 on the humus content. The average percentage of humus to a depth of 

 3 feet in the alfalfa basins, manure basins, and in the control rows is 

 given in Table V. Each percentage figure given in the table is made up 

 of an average of about 21 determinations, each determination repre- 

 senting a composite of at least three samples. 



Table V. — Average percentage of humus to a depth of 3 feet in unmulched soil and in 

 mulched basins in a lemon grove on light sandy loatn soil. Experiment IV 



27811°— 18- 



