SOILS AND CROPS DETERMINE KIND OF FERTILIZER 209 



crop to be grown are two factors determining largely the kind of 

 fertilizer to use (Figs. 135 and 136). The growing of sugar beets 

 on peat, for example, requires liberal applications of a potash 

 fertilizer. The forcing of lettuce and other garden crops requires 

 an abundant supply of available nitrogen (Fig. 142). The appli- 

 cation of soluble phosphate fertilizer on many soils proves the 

 most profitable fertilizer treatment, especially on long-cropped > 

 prairie soils. The improvement of poor soils generally requires 

 the addition of all the fertilizing elements. 



Fig. 142. — Making a second application of fertilizer to head lettuce. The fertilizer is 



scattered along the rows and stirred in. (N. Y.) 



Mixed or complete fertilizers in comparison with single fertil- 

 izers commonly give the highest average increases and profits. 

 This is particularly true in case of wheat, potatoes and cotton. 

 Frequently a mixture of phosphate and potash gives best results. 

 Many experiments have shown that the full effect of one fertilizing 

 element is obtained only when it is associated with the other two. 

 Moreover, the addition of phosphorus and potassium usually 

 increases the need of nitrogen for bigger crops. In other tests a 

 fertilizer, either single or complete, used in conjunction with a 

 green-manuring crop is the best means to obtain higher crop yields. 

 14 



