Decomposition of Sweet Clover as a Green Manure 



145 



the mean gain in nitrates for the pot from which the crop was removed 

 was subtracted from the value for the pot in which the material was 

 turned under. This calculation gave the net gain in nitrates due to the 

 green manure added. These figures appear in the last column of the 

 table. The probable errors were computed according to Peter's formula. 



In the unlimed pots of the three-months period, no nitrates were 

 formed following harv^est, but on the contrary denitrification occurred. 

 For the longer periods, nitrate formation took place to some extent in 

 the unlimed pots both in 19 14 and in 19 16, but the probable errors 

 attached to the values for net gain are so large as to render them of 

 doubtful significance. The favorable effect of lime is indicated in the 

 table, but no significant differences appear for the two kinds. The 

 figures indicate also that a larger net gain in nitrates is obtained by- 

 growing the crop for the longer period. 



The percentage of the nitrogen in the plant material added, which was 

 changed to nitrates during the four-months period following harvest, 

 is shown in table 12. The figures for grams of nitrogen added are taken 



TABLE 12. Percentage of Nitrogen Added in Crop, Changed to Nitrate in 



Four Months 



Treatment 



Duration 



of 

 growth 

 (days) 



Nitrogen added 

 in plant 

 material 

 (grams) 



Net increase 



in nitrate 



nitrogen 



(grams) 



Percentage 

 nitrified 



Unlimed 



Slaked lime 



Ground limestone . . 



Unlimed 



Slaked lime 



Ground limestone . . 



Unlimed 



Slaked lime 



Ground limestone . . 



89 

 89 

 89 

 118 

 118' 

 118 

 116 

 116 

 116 



3216 

 4125 

 4313 

 6408 

 8166 

 8098 

 0.5078 

 I . 0059 

 o . 8608 



± .0060 



± .0185 



± .0022 



± .0006 



± .0241 



± .0066 



± .0101 



± .0656 



± .0117 



None 



0.18839 ± 

 0.28065 ± 

 0.18551 ± 

 0.37749 ± 

 0.56685 ± 

 0.03557 ± 



0.45060 zh 

 O.38211 ± 



03 1 41 

 04603 



06508 



09876 



07142 



02233 



07559 

 02560 



None 

 4567 ± 



65 

 28 

 46 

 70 

 7 

 44 

 44 



7.89 



07 ± 10.68 

 95 ± 10. 16 

 23 ± 12.17 

 00 ± 8.84 

 00 ± 4.40 

 80 ± 8 . 06 

 39 ± 3.04 



from the tables in which the yields are recorded. It is assimied that 

 these figures, obtained by analysis of the crops removed, should approxi- 

 mate the nitrogen added in the material turned under in the duplicate 

 pots. The values for net increase in nitrate nitrogen were obtained from 

 those showing the net gain in nitrates in parts per million due to the 

 crop turned under. The later values were changed to grams of nitrogen 

 by taking account of the amount of soil present in each pot. It is 

 realized, of course, that all of this nitrogen may not have been formed 

 from the plant material added. However, the figures do represent the 

 net increase in nitrate nitrogen as a result of turning under the crops, 

 17 257 



