1922.] 



Notes on Manures for February. 



1037 



The table shows the large amounts of fertiliser material 

 removed from the soil by crops of the specified size, which, 

 though good, are by no means excessive. Stated in terms of 

 phosphoric oxide (P 2 5 ) the figures do not seem imposing: 

 they become much more striking, however, when expressed 

 in the more familiar units of 30 per cent, superphosphate. 



In the case of phosphates and of potash, removal in the crop 

 is the most important source of loss from the soil, there being 

 no significant washing out by rain, etc. In the case of nitrogen 

 and of lime, however, removal by the crop is only one source 

 of loss, drainage water removing much more serious quantities 

 than of potash and phosphates. As against this, however, the 

 clover crop returns a large and usually unknown amount of 

 nitrogen to the soil. The crop figures are therefore of less 

 importance since they represent only one of the three deter- 

 mining factors : they are, however, given here for the sake of 

 completeness : — 



Nitrogen removed: lb. per acre. 



Equivalent to Lime removed : 



sulphate of ammonia lb. per acre. 



Iii grain. In straw. Total. (%0°/ O nitrogen).* as oxide.* as carbonate.* 



Wheat 



41 



19 



60 



300 



11 



20 



Barley 



35 



14 



49 



245 



9 



16 



Oats 



38 



20 



58 



290 



13 



23 



Clover hay- 







98 



490 



90 



160 



Meadow hay 







49 



245 



32 



57 



Swedes 



Roots only 



70 



350 



20 



36 



Mangolds 







112 



560 



18 



32 



Potatoes 



Tubers only 



92 



460 



7 



12 



Although they represent only one source of loss the figures • 

 show that the exhaustion of nitrogen from a cropped soil is 

 considerable, and they emphasise the need of ample nitrogenous 

 manures for arable crops. 



The large amounts of lime removed from the soil by clover 

 and by meadow hay should be noted. 



Spring Dressings for Cereal Crops. — The above table shows 

 the demand for nitrogen made on the soil by a cereal crop : 

 it is not surprising that nitrogenous top dressings give increases 

 in yields. Some of the results obtained during the past season 

 at Kothamsted are : — 



Barley. 



Head corn Total grain Straw Total produce 

 bushels per acre. lb. per acre. cwt. per acre. lb. per acre. 

 No top dressing ... 25'6 1,554 171 3,473 



Top dressing (sulphate 



of ammonia) ... 34-2 2,056 2^8 4.612 



* See p. 832 for explanation of difference between these. 



