30 



grass. A second set was sown with mustard two weeks after the addi- 

 tion of the manures. The weight of crops harvested was as follows: — 



Grass Mustard 

 Grams. Grams. 

 Nitrate of sodium 184 234 



Nitrate of sodium with horse dung 251 357 



Sulphate of ammonium 182 69 



Sulphate of ammonium with horse dung 190 22iJ 

 These few experiments leave much to he desired; but it at all events 

 appears that with a more moderate application of dung, amounting to 

 about 20 tons per acre, the return obtained from nitrate of sodium and 

 sulphate of ammonium is not decreased, indeed, in every instance the 

 dung has itself contributed to the increase of crop. 



ROTHAMSTED RESULTS BEARING ON THE QUESTION. 



The field experiments at Rothamsted furnish abundant examples of 

 the action of farmyard manure on various crops, and also of the after- 

 effect of residues of the manure remaining in the soil. The alteration in 

 the character of the soil by the continued use of farmyard manure, and 

 the relative production of nitrates in manured and unmanured land, are 

 also well shown in these experiments. Keeping, however, to the points 

 before us, we shall here simply inquire what have been the results of the 

 Rothamsted experiments on the employment of farmyard manure with 

 nitrate of sodium, and with other nitrogenous manures ; and what have 

 been the results of the application of straw in conjunction with nitrogen- 

 ous manures. 



The practical question whether farmyard manure can be used econ- 

 onomicaiiy with artificial manures is one of great importance to the 

 farmer, and can only be satisfactorily settled by field experiments. The 

 irregularities of field experiments are, however, very great, and the most 

 potent cause of irregularity, namely, the great variety in the seasons, 

 and especially the wholly variable and uncertain distribution of rain, is 

 unfortunately beyond the control of the experimenter, and assumes its 

 greatest proportion where large quantities of manure have been applied. 

 It is necessary therefore, to take the average result of many years if* 

 trustworthy conclusions are to be drawn from field experiments. 



In the field devoted to the culture of roots at Rothamsted 

 a considerable portion of the land has received annuallv for many years 

 14 tons of farmyard manure per acre. One-half of this land has received 

 in addition 3^ cwt. of superphosphate each year. These two farmyard 

 manure plots are each divided into five portions, one receiving no fur- 

 ther manure, the others cross-dressed respectively with nitrate of sodium, 

 sulphate of ammonium, rape cake, and sulphate of ammonium with rape- 

 cake. Each cross-dressing supplies a known quantity of nitrogen. 

 What has been the effect of these cross-dressings ? 



From a practical point of view the farmer will be content to ascer- 

 tain what increased weight of roots has been obtained by the use of each 

 cross dressing, and to compare the value of the roots with the cost of the 



