PLANT FOOD AND MANURES 135 



placing the boxes, excessive evaporation from the soil in 

 them is prevented. A well-drained spot should be 

 selected for the boxes in order to guard against water 

 accumulating under and around them. If the soil is 

 very clayey this object may be secured by putting under 

 each box a layer of small stones. It is also necessary to 

 arrange the boxes so that the drainage-water from one 

 will not run under the next. Mark the boxes A, B, C, 

 and D. 



In all such experiments too much care cannot be 

 taken to secure uniform conditions for the boxes or 

 plots to be experimented upon. For instance, if one 

 box is shaded and another not, and they are treated 

 differently as regards manuring, it is impossible to be 

 certain afterwards whether any difference in their crops 

 is due to the different manures used or to the difference 

 of lighting. 



Fill the boxes with the washed sand, and to this 

 add the various substances whose effects we wish to 

 try. 



To the soil in A, add nothing. This is the control 



or standard. 



To B, add about 8 Ib. of well-rotted farmyard or stable 



manure. Carefully fork the manure into the sand, or 



remove the soil and mix the manure with it in a dry 



place, and then return to the box. 



To C, add 2 oz. of finely-powdered chalk or marl, 



scattering it evenly over the surface, and stir in lightly 



with a fork. Then add J oz. of sulphate of ammonia. 

 To D, add about 2 oz. of finely-powdered chalk or 



marl ; mix well, and then apply J oz. basic slag, J oz. 



