ON ACCUMULATION OF NITRATES 81 



There is a slightly greater accumulation of nitrate in the pot 

 representing the untreated soil at Martin's Hearne than in the corre- 

 sponding pot for Horndon-on-the-Hill, which may be due to the fact 

 that the former is a more open soil. On the other hand, it may be 

 due to the fact that, although the soil at Martin's Hearne is sour, 

 it has a considerably higher content of total and available phosphoric 

 acid than the soil at Horndon. The figures are as follows: 



MARTIN'S HEARNE HORNDON-ON-THE-HILL 



/ / 



Total P 2 O, -089 -078 



Available P 2 O 5 -0046 -0030 



Lime requirement ... 0-27 0-00 



At no period throughout the season does the nitrate content of 

 the untreated soil from Horndon ever approach that of the soil 

 receiving basic slag. The two pots representing the treated and un- 

 treated soils from Martin's Hearne behave somewhat differently. 

 Until August llth the figures are comparable with those representing 

 the Horndon pots, but during the hot spell which succeeded, there is 

 a rapid accumulation of nitrate in both the Martin's Hearne pots, 

 and when sampled on August 25th and September 9th and 15th, 

 the nitrate content of the slag and untreated pots was approxi- 

 mately the same. The temperature during the period August llth 

 to September 15th was higher than at any other period during the 

 season, and although the pot drains did not run, there was a sufficient 

 precipitation to keep the soil moist. On August 18th-19th -88 inch 

 of rain fell, and there was a fall of -10 inch on two consecutive days 

 out of the remaining 13 days in August. Four out of the first five 

 days in September were showery with a total precipitation of -21 

 inch. There was no further rain until September 14th, when -13 inch 

 fell. After the 15th September (which was the last date on which the 

 nitrate content of the two pots was similar) until the 22nd the weather 

 was wet, 3-19 inches of rain falling between the 15th and 22nd 

 inclusive. The drains from both pots ran freely, but unfortunately 

 the drainage water was not collected. From the 22nd to the 27th 

 the weather was dry and hot, no rain falling, and on the 27th when 

 the pots were sampled the slag pot contained 26-32 parts per million 

 of nitrate and the untreated pot 10-64 parts. The relative nitrate 

 content of the two pots was therefore similar to what it had been 

 up to August llth. 



It is difficult to account for the curious results obtained during 

 the period August llth to September 15th. It may be that under 



R.B.S. 6 



