Green M a nuein g . 



[June, 



refers to the part of the phosphate which is soluble in the citric 

 acid used in the official test. Thus a 20 per cent, slag of 20 per 

 cent, solubility is a slag 100 lb. of which contains as much phos- 

 phorus as does 20 lb. of tricalcic phosphate, and that 20 percent, 

 of this phosphatic material is soluble in the official testing liquid. 

 A 20 per cent, slag of 80 per cent, solubility would also contain 

 in 100 lb. as much phosphorus as does 20 per cent, tricalcic 

 phosphate, but, of this, 80 per cent, is soluble under the con- 

 ditions of the official test. This test was designed for the old 

 Bessemer slag and is not equally suitable for the present-day 

 open-hearth slags; data for revision will be available when more 

 field experiments are carried out. In the meantime farmers 

 should regard the solubility figures as having a descriptive 

 rather than an exact value ; a slag of 70 per cent, solubility is 

 probably quicker in action than one of 35 per cent, solubility, 

 but it has not necessarily double the value as the figures suggest . 



Mineral Phosphates, — These have been used with good re- 

 sults in the United States under the name of rock phospnate ; 

 they have also proved effective in France. In the Essex trials 

 they gave promising results, though up to the present they have 

 not acted as well as the high soluble basic slag. A number of 

 tests are in progress in different counties and the results should 

 be carefully watched by farmers. The present indications are 

 that fineness of grinding is important and that^the value per 

 unit of phosphate is less than in basic slag. 



(This article replaces in this issue the usual notes on manures 

 contributed to the Journal by Dr. Russell.) 



* * * * * * 



GREEN MANURING. 

 PART II. 



EL J. Page, M.B.E., B.Sc, A.I.C., 

 Rothamsted Experimental Station. 



The Mode of Action of Green Manures. — The effect of a 

 green manure on the succeeding crop as compared with that of 

 farmyard manure can be considered under three heads, accord- 

 ing to its influence on (1) the supply of mineral nutrients to 

 the main crop; (2) the supply of nitrogen to the main crop; 

 (8) the physical properties of the soil — tilth, moisture-holding 

 capacity, etc. 



