Dec. 2, i9i8 Relation of Inorganic Soil Colloids to Plowsole 



507 



through filter paper. Unfortunately these soil samples were discarded 

 before this apparent error was detected, the analytical work having 

 been done in May, 191 6, and the results not having been carefully tabu- 

 lated and compared until April, 191 7, owing to other work. 



Table I. — Analysis of water extracts of soil mulch, plowsole, and subsoil from orange 

 groves. Average of four groves 



[Results reduced to basis of dry soil and expressed as p. p. m.J 



"■ Leaving out one exceptionally high determination, the average of the other three groves is 1.07 p. p. m. 

 of iron (see text). 



Flowerpots were filled with soil from some of these groves, placed 

 in the laboratory, irrigated several times, and kept mulched. A number 

 of inorganic salts, carbonates, chlorids, nitrates, and phosphates, were 

 mixed with some of the soils. Plowsole layers formed readily under the 

 soil mulch. 



After about one month the soil mulch, plowsole, and subsoil were 

 separately extracted with distilled water and analyzed. There was no 

 accumulation of the water-soluble cementing elements in the plowsole 

 layers in either the treated or untreated soils. 



The plowsole layers in the differently treated soils varied greatly in 

 hardness. The hardest layers occurred in the soils treated with sodium 

 chlorid, sodium nitrate, sodium phosphate, magnesium sulphate, and 

 sodium carbonate. The softest layers were formed in the soils mixed 

 with calcium carbonate, calcium sulphate, and alfalfa. 



Soils from the four orange groves, the soil analysis of which were 

 presented in Table I, were extracted with i per cent hydrochloric acid 

 until calcium was absent, washed with distilled water, and then ex- 

 tracted with 4 per cent ammonium hydrate. The ratio of soil to am- 

 monium hydrate was loo gm. to 500 cc. The "humus" extracts were 

 evaporated to dryness and ignited just enough to drive off the organic 

 matter. There were no facilities on hand at the time for fusion, so the 

 residues were digested with nitrohydrochloric acid on the water bath 

 until no perceptible residue remained. 



Partial analyses of these dissolved residues are given in Table II. 

 Each figure represents the average percentage obtained on the analysis 

 of extracts of soils from eight groves. 



