350 Reading-Course for Farmers, 



a decrease of the humus. There is no difference between the kinds of 

 plant-foods required by corn and those required by potatoes. All plants 

 use the same substances, though the proportion of the different kinds 

 may sometimes vary. 



Hozv can we know what fertilizers to apply? 



The utility of the different kinds of fertilizer constituents is deter- 

 mined as much by the kind of soil on which they are to be used, as 

 by the kind of crop to be grown. 



A soil rich in humus, as a muck-soil, has no need of more nitrogen. 

 It usually has enough, often too much for the amounts of phosphoric 

 acid and potash that it contains. 



Probably the best substances to render the nitrogen of muck avail- 

 able are wood-ashes and lime. 



A light sand or sandy loam, when the humus has been partly 

 exhausted, usually stands in need of nitrogen. 



Specific rules cannot always be given for the choice of fertilizing 

 elements. Only in a general way, some suggestions, as the following 

 may be given: 



1. Soils poor in humus need nitrogen. Fertilizers give a temporary 



supply. A more permanent supply comes only with a renewed 

 increase in the humus supply of the soil. This increase is to be 

 found in the incorporation of manures, the turning under of 

 green crops, and in the decay of roots. 

 Crops that show short growth and fail to develop abundant foliage, 

 may be in need of nitrogen. Sometimes the soil lacks the neces- 

 sary amount, and sometimes it is present, but not becomings avail- 

 able through decay of the humus. In the latter case, the cause 

 may be need of drainage, lack of lime, or insufficient tillage. 



2. Phosphoric acid is used abundantly by the cereals and, in general, 



by crops that mature their seeds. It frequently is deficient in 

 sandy soils, where it may be preceded or followed by an applica- 

 tion of lime. No form of lime, except plaster, should ever be 

 mixed with fertilizers that contain phosphoric acid, before they 

 are used. 



3. Potash is used most abundantly by plants that develop starch and 



sugar, as potatoes and beets. Most New York state soils, except 

 light sand, contain more potash than phosphoric acid and as a 

 rule are more benefited by the application of phosphoric acid than 

 potash. Moreover, every one hundred pounds of dissolved rock 

 contain about fifty pounds of last plaster, which, on many soils, 

 has a tendency to unlock the potash and make it available. 



