336 SOILS. 



fertilizers; such examination will at the same time serve to 

 determine the greater or less uniformity of soil-conditions, 

 which is of first importance to the cogency of fertilizer tests. 

 As a matter of fact, few farmers possess the necessary qualifi- 

 cations to carry out such tests successfully, since their execu- 

 tion requires a certain familiarity not only with the principles 

 and methods of experimentation, but also the faculty and 

 practice of close and reasoning observation; which, unfortu- 

 nately, is not as yet a part of instruction in our schools. The 

 experience so often had in co-operative work between experi- 

 ment stations and farmers is cogent on this point. 



Those desiring to do such work, however, can make use of 

 something like the plan given above ; it being understood that 

 in the case of clay soils, the unplanted paths left between the 

 plots should be at least two feet in width ; in the case of sandy 

 soils the distance should be not less than three feet, and more 

 if the plots are located on a slope. The crop from each plot 

 should if possible be weighed as a whole; but if the plot be 

 large and the crop measurably uniform, an aliquot part, such 

 as one fourth, may be weighed instead. In regular experi- 

 mentation the crops are weighed both in the green (freshly 

 cut) condition, and after drying. Since the dry matter is the 

 real basis of value in the case of most field crops, its weight 

 is the most important; as the water-content of green crops 

 may vary considerably. But in the case of vegetables as well 

 as fruit crops, not only must the weight of the fresh crop be 

 determined, but it should be sorted into the " marketable " and 

 " unmarketable " sizes and qualities. Failure to do this may 

 vitiate the entire experiment for practical purposes. 



Pot Culture Tests. The uncertainty attending plot culture 

 tests on account of the difficulty of controlling seasonal and 

 other external conditions, has resulted in the extended adoption 

 of indoor culture tests, usually conducted in zinc or " gal- 

 vanized " cylinders of a size sufficient to contain from twelve 

 to twenty or more pounds of soil. These are kept in a green- 

 house whose temperature and moisture-condition can be regu- 

 lated at will, and where the soil-moisture is wholly under con- 

 trol. For investigations of the effects of various kinds of plant- 

 food upon vegetable development, this method has served most 

 satisfactorily and effectually, and striking photographs of re- 



