192-2.] 



Notes on Manures for December. 



837 



result. Obviously, however, the main elt'ect is produced by the 

 11 or 3 cwt. per acre, and further additions of manure might 

 well prove to be unprofitable. 



The evidence indicates that there are two distinct sets of 

 maximum returns for successive increments of manures : — a 

 maximum increment of crop which is given not necessarily, and 

 probably not usually, by the first, but by the second or some 

 subsequent increment of manure ; and a maximum of profit which 

 may be obtained with some prarticular increment of manure. 



Effect of Potassic Fertilisers on Clover. — One of the most 

 striking results at Eothamsted this year was the effect of potassic 

 fertilisers in increasing the yield of clover in a pure red clover 

 ley. The plant to begin with was poor ; it was kept over from the 

 19-20 sowing and left to stand after being cut in 1921 because the 

 young seeds of that year completely perished in the drought. It 

 was sufficiently good to save under the circumstances, but was 

 not very vigorous. The results of treating it with fertilisers 

 showed that slags of various kinds gave no improvement, but 

 potassic fertilisers improved the yield. The results were : — 



clover hay : ciot. per acre. 



Xo added manure ... ... ... ... 17*0 



Basic slag ... ... ... ... ... 17"0 



Sulphate of potash... ... ... ... 23 "2 



an increase of over 6 cwt. of clover hay per acre for an addition 

 of 1 cwt. of sulphate of potash. 



Apparent Failure of Basic Slag on Grass Land. — Cases have 

 recently been reported in which farmers applied basic slag to 

 grass land last winter, but have seen no result. The past season 

 was not very favourable to slag, and in the Rothamsted experi- 

 ments slag gave very little result. The cold spring was 

 unfavourable to growth in many districts, and it was not till 

 the end of May that the grass began to make much gi'owth : it 

 then came on with a rush. In these circumstances the slag 

 does not seem to have exerted its effect, and only one of the 

 various samples tested in the field at Eothamsted gave any 

 marked increase. 



There are, however, cases where even in good seasons slag 

 does not act as well as it might be expected to do. Some of these 

 were mentioned in last month's notes : they were cases in which 

 lime was needed before the slag could act. Another possibility 

 is sugsjested by the clover experiment just mentioned : here slag 

 bv itself was without action in increasini>' the gi'owth of clover, 

 though potash was effective. It is possible, therefore, that some 



