Feb. t5, X918 



Humus in Mulched Basins 



509 



Table II. — Working error in making humus determ,inations 



Soil No. 



677 

 677 

 678 

 678 

 679 

 679 

 670 

 670 

 671 

 671 

 672 

 672 



Per cent. 



0.358 



•358 



. 041 



•039 

 •045 

 . 046 



• 250 



• 250 

 .030 

 .028 

 .048 

 . 046 



vSoil No. 



676 

 676 

 677 

 677 

 678 

 678 

 682 

 682 

 683 

 683 

 684 

 684 



Per cent. 

 o. 227 



. 227 



.051 



. 050 



.023 



. 022 

 . 192 

 . 200 



.056 

 .051 



. 022 

 . 021 



Soil No. 



685 

 685 

 686 

 686 

 687 

 687 

 688 

 688 

 689 

 689 

 690 

 690 



Humus. 



Per cent, 

 o. 284 

 .284 

 .081 

 .081 

 .050 

 .050 

 .284 

 .384 

 .074 

 . 070 

 •043 

 . 04a 



From these considerations it might therefore be expected that the 

 amount of humus in the soil in the basins would be subject to fluctua- 

 tion, the amount present at any one time depending upon the ascendency 

 of one or the other of these important groups of soil organisms. 



The fluctuation in the percentage of humus makes it impracticable to 

 attempt to determine the rate at which humus was formed between 

 specific dates. It will be seen in Table I that there is frequently a de- 

 crease in the percentage of humus from one period to another, especially 

 during the second year, a point that might possibly apply to determina- 

 tions made by Gortner (5). He added silk, wool, flour, and alfalfa meal 

 to soils, kept the materials in earthenware jars, and at the end of a year 

 made humus determinations. In most instances he found less humus 

 at the end of the year than he found in the treated soils when the experi- 

 ment was started. It would have been of much interest if these deter- 

 minations had been made frequently during the year. None of the 

 losses of humus reported by him are greater than was sometimes found 

 in a month's time in humification studies carried out under laboratory 

 control in this Office, to be reported later. 



A comparison of the amount of humus in the basins from year to year 

 is made by averaging the percentage found during each of the years 

 1915 and 1916, as shown in Table I. At the bottom of the table will be 

 found the ratio of the average percentage of humus in 1916 to that in 



1915- 



Experiment II. — In April, 191 5, a block of orange trees in another 

 grove on sandy loarri soil was basined. The basins were about 12 feet 

 in diameter, and the treatments were the same as in Experiment I, 

 except that less lime was used. 



The results of the humus determinations are given in Table III, which 

 shows the fluctuation in the amount of humus from time to time. The 

 ratio of the average percentage of humus in the basins in 191 6 to that 

 in 1 91 5 is given in the bottom line in the table. 



