SOILS AND FERTILIZERS 403 



hence they always do their best work and are most profitable on soils 

 which are in good average condition, neither too heavy and wet nor 

 too light and dry. Furthermore, the continuous growth of annual 

 crops, whether hoed or broadcast, adds no vegetable matter to the 

 soil, except in the roots and stubble, and it is common to find that 

 the first crop of corn, on sod land, with commercial fertilizers, is 

 superior to that of the second year, undoubtedly because the vege- 

 table matter of the old turf helped maintain a satisfactory moisture 

 condition in the first year and was largely destroyed before the 

 second year. 



The most economical use of commercial fertilizers is only 

 reached when they are applied in rotation in which the soil is main- 

 tained in good moisture condition by the use of barnyard manure 

 or the vegetable matter from crops grown for the purpose. Al- 

 though the food elements in a commercial fertilizer form but one of 

 the several conditions needed for the best development of the crop, 

 it is important that these elements should be suited to the demands 

 of the crop at every stage of its growth, else the product will not be as 

 large as the other conditions would permit. It is the most common 

 practice to use this class of fertilizers with the annual crops, %nd 

 there are good reasons for such practice, as shown by fertilizer ex- 

 periments. 



Annual crops, whether oats, corn, potatoes, or vegetables, re- 

 quire that their food elements shall be ready to hand as their 

 growth makes new demands. The commercial fertilizer, then, 

 should be able to furnish available food elements throughout the 

 growing season, and in the proper proportion required by the crop. 

 A study of the chemistry of plant growth shows very clearly that 

 there must be present a continuous supply of available nitrogen, 

 which requires that some shall be in the inorganic and some in 

 organic form. 



The more quickly the crop is to be grown in the spring the 

 more inorganic nitrogen will be needed, since it is sooner ready for 

 the plants than organic forms. Soluble phosphoric acid produces' 

 results more quickly and thoroughly than the other forms, and a 

 well-made fertilizer should have at least half of its available phos- 

 phoric acid in the soluble form. All crops remove from the soil 

 much more potash than phosphoric acid, and although the soil may 

 furnish some of it, without the positive evidence of field experi- 

 ments to that effect, a fertilizer should have at least as much potash 

 as it has soluble phosphoric acid. 



Commercial fertilizers may be advantageously used in top- 

 dressing grass and for such a purpose it should have a high percent- 

 age of nitrogen, of which nearly all should be inorganic. The phos- 

 phoric acid should be nearly all soluble in order to be of marked 

 benefit, and the fertilizer should be applied in early spring while 

 the soil is thoroughly moist. 



Finally, in the purchase of fertilizers it should be borne in mind 

 that it costs just as much to mix, bag, freight, and handle a ton 

 of low-grade fertilizer as one of high grade. By purchasing a half 



