222 



Methods of Field Manurial Trials. 



possible, say one-third to two-thirds of an acre ; but this implies 

 a uniform field of two to five acres, and such an area is usually 

 difficult to secure. Dr. Wagner finds that in his own experi- 

 ments plots of xrTo hectare acre) gave more exact and 

 trustworthy data ; the cost of the experiment is also thus 

 reduced, while the plots are more easily managed, and allow 

 the results to be seen at a glance. 



Care should be taken to mark out the size of the plots 

 accurately with the help of pegs, and experimenters should 

 not trust to the eye to get right angles. The plots should pre- 

 ferably be square when this is possible, and similarly manured 

 plots should be as far as possible from each other. 



In preparing the manures all salts should be passed through 

 a 4 mm. inch) mesh sieve, and sampled. The quantity for each 

 plot should then be carefully weighed and mixed with about 

 15 — 20% of damp peat mould. The mixture should then be 

 securely fastened up in thick jute bags. 



The sowing of the manure on the plots should be entrusted 

 to an experienced man, who should distribute it as uniformly as 

 possible. The manure must not be powdery ; if it is too dry, a 

 little damp earth may be carefully mixed with it ; and it should 

 not be put on in windy or damp weather. After spreading the 

 manure the sacks should be at once thoroughly washed. 



The question of how far from the edge of the plot the 

 manuring should stop depends upon circumstances. If the 

 manure is to be spread on the rough furrow and mixed with the 

 soil merely by harrowing in, or when it is merely a case of top 

 dressing with nitrate of soda, it can be put within 10 cm. (four 

 inches) of the edge. But in such cases the experiment must 

 not last more than a year. If it is to last longer on the same 

 ground, or if the field is to be ploughed after the manure is put 

 on. then it must be remembered that the ploughshare moves the 

 soil for a certain distance in front, and throws it also for a cer- 

 tain distance on the side, and Dr. Wagner therefore leaves a 

 corresponding strip all round. In this way are treated all 

 manures which are capable of leaving residues which act in 

 after years, such as potash, phosphoric acid, lime, and organic 

 nitrogen, as well as those which are applied prior to ploughing. 



Care must be taken, in ploughing such fields, to use through- 



