Decomposition of Sweet Clover as a Green Manure 141 



These results substantiate those obtained in 19 14. A comparison of 

 tables 3 and 6 shows that lime produced a somewhat greater effect in 

 19 1 6 than in the previous season. The figures for percentage of nitrogen 

 are similar except as regards the unlimed pots. It was noted that the 

 plants growing on the unlimed soil appeared less vigorous in 19 16 than 

 in 19 1 4. That they were poor in color, indicating lack of nitrogen, has 

 already been stated. The figures for fiber content agree fairly closely 

 with those obtained the previous season. 



The samples of soil taken at harvest were examined for nitrates in 

 the moist condition. Inasmuch as the drying of a soil is known to affect 

 its nitrate content, it was thought that this procedure might give more 

 accurate and more uniform results than were obtained in 19 14. Following 

 harvest the pots were maintained at a moisture content of 30 per cent 

 for four months. During this period all possible care was taken to keep 

 conditions similar in the different pots. In sampling the soil at the end 

 of the four-months period, no tops still showing their original form were 

 found; however, several undecomposed root crowns were found in each 

 of the pots in which the plants had been turned under. The samples of 

 soil taken at this period were also examined for nitrates immediately 

 after sampling. The results of these determinations are given in table 7 : 



TABLE 7. Formation of Nitrates 

 (Crop turned under after 116 days growth) 



Pot 



40 



41 

 42 



43 

 44 

 45 

 46 



47 

 48 



49 

 50 

 51 



Treatment 



Unlimed 



Unlimed 



Unlimed 



Unlimed 



Slaked lime 



Slaked lime 



Slaked lime 



Slaked lime 



Ground limestone 

 Ground limestone 

 Ground limestone 

 Ground limestone 



Treatment of crop 

 at harvest 



Removed 



Removed 



Turned under 

 Turned under 



Removed 



Removed 



Turned under 

 Turned under 



Removed 



Removed 



Turned under 

 Turned under 



Nitrates 



at 



harvest 



(parts per 



million) 



5 

 7 

 5 

 4 

 17 

 II 



9 



17 

 8 



14 



8 



9 



Nitrates 



after 



four months 



(parts per 



million) 



20 

 24 

 47 

 25 

 60 



41 



283 

 230 



52 

 60 



240 

 228 



The soil used in 19 16 contained 3 parts of nitrates per million. It 

 is seen from the table that there was an increase as a result of growing 

 the crop, and that the increase was more marked in the lim*ed pots. 

 The results obtained for nitrate formation due to turning under the crop 

 follow, in general, those obtained in the previous season. A statistical 

 study of this table is made in the general discussion of results. 



253 



