42 THE ESSEX EXPERIMENTS 



rain on May 26th (1 inch) was lost by surface drainage. At Lambourne 

 End the soil is not heavy and its peaty character no doubt enabled 

 it to retain a much greater proportion of the rain which fell on the 26th. 

 Over a period of three years the heaviest average crop of hay has 

 come from the plot receiving open hearth (fluorspar) basic slag of 

 20 % solubility the slag which has given comparatively poor results 

 at other centres (Martin's Hearne, Table X, and Horndon, Table XIV). 

 As if to emphasise the peculiarity the next best return is given by 

 the least soluble of the mineral phosphates used in the experiments. 

 At Lambourne End citric solubility is clearly of minor importance 

 and the difference in the behaviour of the open hearth (fluorspar) 

 basic slag (Plot 1) at this centre and at Martin's Hearne is probably 

 accounted for by soil conditions. The Lambourne End soil has a 

 much higher lime requirement figure (-45 % compared with -27 % 

 at Martin's Hearne) but it is by no means certain that this difference 

 alone suffices to explain the results. 



DISCUSSION OF THE RESULTS ON THE LONDON CLAY SOILS 



At all the centres on the London clay formation there has been 

 a marked response to phosphates. The effect of the manures on the 

 whole is even more striking than on the boulder clay soils. Differ- 

 ences between the relative efficiency of the various phosphates have 

 been noticeable. Where the pasture has been down for many years, 

 and where as a consequence big stores of organic matter have 

 accumulated and the soil has a high 'lime requirement,' and where 

 the rainfall is adequate, then rock phosphates prove quite as efficient 

 as the best grades of basic slag. Under these conditions open hearth 

 (fluorspar) basic slags do not give consistent results. One type of 

 open hearth fluorspar slag of very low solubility proves quite as 

 efficient as the highest citric soluble type of slag, whilst another 

 open hearth fluorspar slag, apparently more soluble than the former 

 one, proves decidedly inferior. 



Where the pasture is comparatively new (30 years or so), where 

 the summer rainfall is low, and where a small reserve of calcium 

 carbonate still exists in the soil, the best results are secured by the 

 highest citric soluble types of basic slag. The improvement effected 

 by the best grades of basic slag is, however, closely approximated 

 to by the North African rock phosphates. In fact in some years, 

 noticeably at Latchingdon, rock phosphates may do considerably 

 better than the best grades of basic slag (Table XVI). 



