ON ACCUMULATION OF NITRATES 77 



The figures suffice to demonstrate that there is no difference between 

 rock phosphates and basic slag so far as their effect on the collection 

 of nitrogen is concerned, a conclusion which is borne out by the 

 botanical analysis of the 1920 hay crop (Table XXXI, Fig. 11) and 

 also by the botanical examination of the pasture in 1919 (Table XV, 

 Plate VI). 



TABLE XLIL PERCENTAGE OF NITROGEN 

 IN VARIOUS PLOTS AT HORNDON 



Plot % nitrogen 



1 Florida pebble phosphate -240 



3 Algerian phosphate ... -239 



5 Basic slag -244 



6 Untreated -212 



7) 



8 j Gafsa rock phosphate ... -227 



11 Egyptian phosphate ... -247 



13 Superphosphate ... -226 



15 Superphosphate and lime -222 



16 Untreated -208 



17 Basic slag -226 



Average of Rock phosphate plots ... -238 



two basic slag ... -235 



untreated -210 



THE RELATION OF PHOSPHATES TO THE ACCUMU- 

 LATION OF NITRATES IN GRASS-LAND 



It has been suggested by Middleton(i5) that the secondary action 

 of basic slag on pastures is due to the nitrification of the nitrogen 

 accumulated by the nodule organisms, and that this resulting nitrate 

 nitrogen is responsible for the vigorous growth of grasses which 

 follows after the clover has been stimulated. 



In order to ascertain what effect the application of phosphates had 

 on the production of nitrates in grass-land it was decided to make 

 as far as possible weekly determinations of the nitrate nitrogen con- 

 tent of the soil on the basic slag and untreated plots at three of the 

 experimental centres. The centres selected were Martin's Hearne, 

 where the soil has a lime requirement of -27 %, Lambourne End, a 

 more sour type of soil with a lime requirement of -45 %, and Horndon- 

 on-the-Hill, a 'sweet' soil containing a small reserve of calcium 

 carbonate. 



