390 SOILS 



soils need potash and phosphoric acid more than 

 nitrogen, especially potash. 



Questioning the Soil. A good farmer will not 

 long be satisfied to fertilise solely on hearsay evi- 

 dence. He will observe the effects of different fer- 

 tilisers on his own crops and, gradually learning the 

 peculiar needs of his soil, will fertilise accordingly. 

 It is not necessary to lay out an elaborate series 

 of plot experiments with fertilisers in order 

 to determine with considerable accuracy what 

 fertiliser pays best on a certain soil. In many 

 cases it is enough merely to test different fertilisers 

 as a part of the regular farm practice; in other 

 cases it will pay to lay out fertiliser plots. In 

 either case, the testing should be done methodi- 

 cally and the results should not be interpreted too 

 hastily. 



A common way of testing fertilisers is to use 

 different kinds indiscriminately, until one is found 

 that answers the purpose. This hit-or-miss method 

 is usually unsatisfactory. Another way is to 

 apply each of the three plant foods separately 

 and in combinations. This is an exact and 

 reliable method. In these experiments it is cus- 

 tomary to use nitrate of soda, sulphate of potash, 

 and superphosphate as the sources of plant food, 

 since these materials each contain but one kind 

 of plant food. 



These fertilisers may be applied to different 

 rows of plants, or to plots of the same size. Plots 

 one rod wide and eight rods long, containing 

 TfV of an acre, are a convenient size. The plots 

 should be long and narrow, so as to cover 

 inequalities of soil. If the land is sloping, run them 

 up and down the slope. Make every condition 

 in the several plots as nearly alike as possible, 



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