Feb. 25, 1918 Humus in Mulched Basins 507 



uniform tint was always obtained from the soils studied in making humus 

 extracts from them. The straw color produced by the extraction of soil 

 with I to 2 per cent of undecomposed organic matter added was found 

 to be so thoroughly obscured by the humus color of the soil that its pres- 

 ence did not interfere with the colorimetric reading. 



It is well recognized that when hay material of many kinds is digested 

 with hot hydrochloric acid and extracted with ammonia, a solution is 

 obtained which in appearance and color can not be distinguished from 

 a humus extract from a soil. 



Much of the literature relating to humus is discussed by Schreiner and 

 Shorey (/o). 



HUMUS FORMATION IN MULCHED BASINS 



Experiment I. — Mulched basins, 15 feet in diameter, were installed 

 in an orange grove near Riverside, Cal., in March, 191 5. The soil is a 

 red clay loam, derived from granite, which underlies the soil at a depth 

 of 3 to 4 feet. One half of the basins were mulched with about 180 

 pounds of alfalfa (Medicago saliva) each and the other half with about 

 20 cubic feet of good cow manure each. One half of the basins in each 

 mulching series received 200 pounds of lime dust each. This lime was a 

 by-product from the flues of a neighboring cement plant. It was com- 

 posed of about 45 per cent of calcium carbonate, about 20 per cent of 

 calcium hydrate, about 10 per cent of calcium sulphate, about i per cent 

 of potash, and a little phosphoric acid. The balance was mostly silicious 

 material. 



During Augus^. of the same year another row of orange trees in the same 

 grove was basined and mulched with alfalfa. These basins were smaller 

 than those just referred to, and less mulch was used. Part of these 

 basins received about 100 pounds each of ground hme rock analyzing 

 about 90 per cent calcium carbonate. The rest of the basins in the row 

 were unlimed. 



All surface organic matter was carefully removed, and soil samples 

 were taken to a depth of 3 feet in these basins, usually from three basins 

 in each experiment, the samples being separated into foot sections. 

 Corresponding foot samples from the three basins were composited, and 

 each composite sample was analyzed in duplicate. The percentage 

 reported in the following tables are the averages to a depth of 3 feet. 

 Usually the samples were collected just before irrigation. 



Table I shows the average percentage of humus from time to time to a 

 depth of 3 feet of soil in the basins under the various treatments during a 

 period of from 12 to 17 months. 



The low humus percentage is due in part to the removal of several 

 inches of the surface soil in constructing the basins, which suggests inci- 

 dentally that in making basins as little surface soil as possible should 

 be removed. 



