70 



EFFECT OF PHOSPHATES 



2 8 



12 26 

 April 



10 24- 

 May 



7 21 



June 



$ /9 

 July 



16 30 13, 274 



March April May June July August Sept. Oct. 



FIG. 16. Temperature of the Soil at a Depth of 9 inches on the Untreated and Basic 



Slag Plots at Great Mulgraves, Horndon-on-the-Hill. Soil London clay. 



Plot 16, Untreated Plot 17, Basic Slag . 



inches of soil on the slag plot remained considerably cooler than the 

 surface soil on the untreated plot. The importance of securing an 

 efficient covering of the surface soil, so as to protect it from the direct 

 rays of the sun, is well brought out in Fig. 15. The thick bottom of 

 clover has not only succeeded in retaining the moisture on Plot 17, 

 but it has very effectively kept the plot cool during the hot spell 

 of weather in May and June. A comparison of Figs. 13 and 15 shows 

 quite clearly moreover that the lower temperature of the surface 

 soil on Plot 17 is not due to the higher moisture which it contains, 

 but is almost entirely due to the superior covering effect of the crop 

 on this plot. 



During the hot period May 1 7th-25th the temperature of the surface 

 soil on both plots rose considerably, and on the 25th there was a 

 difference of 3-1 C. between them. The subsequent week was showery, 

 a total of -24 inch falling on four of the seven days. Of this amount 

 14 inch fell on the 29th. On the 31st the temperature of Plot 17 

 had fallen from 17-2 C. the previous week to 15-4. Plot 16 on the 

 other hand had risen from 20-3 on the 25th to 21-4 on the 31st 

 there being now a difference of 6-0 C. between the two plots. In 

 degrees Fahrenheit the temperatures at a depth of 3 inches on the 

 two plots were on Plot 16, 70-5 and on Plot 17, 59-7. 



During the whole of May and June, Plot 17 (slag) at a depth of 

 3 inches was never less than 3 C. cooler than the untreated plot. 

 During the wet month of July the temperature on the two plots 

 more closely approximated, but whenever a warm and dry spell of 



