FIELD TESTS WITH FERTILIZERS 221 



283. Deficiency of Two Elements. — If the prelim- 

 inary trials indicate a deficiency of two elements as 

 nitrogen and phosphoric acid, both elements are used 

 together, in the same way as described for deficiency 

 of nitrogen, with additional plots for the separate ap- 

 plication of nitrogen and phosphoric acid. 



284. Importance of Field Trials. — While it seems a 

 troublesome matter to determine the actual needs of a 

 soil, it will be found that both time and money are 

 saved by a systematic study of the question. Suppose 

 fertilizers are used in a " hit or miss" way year after 

 year on a soil, deficient only in phosphoric acid. It 

 would take 8 years to find out what the soil was 

 deficient in, if a different fertilizer were used each year, 

 and during all this period, either the soil has failed to 

 receive its proper fertilizer, or expensive and unneces- 

 sary plant food has been provided. 



285. Will it Pay to Use Commercial Fertilizers? 



— This question can be answered only by trial. If a 

 soil is in need of available plant food, the additional 

 amount of crop produced should pay for the fertilizer 

 and the expense of nsing it. Some fertilizers have an 

 influence on two or three succeeding crops, and only 

 partial returns are received the first year. When large 

 crops must be produced on small areas, as in truck 

 farming, commercial fertilizers are generally neces- 

 sary. In the production of large areas of staple crops 

 as wheat and corn, in the western prairie states, 



