CHAPTER IT. 



CHEMICAL AND MINERAL NATURE OF SOILS. 



73. Unsatisfactory State of Present Knowledge. It is 

 now pretty generally conceded that the capacity of a 

 soil to feed crops of a given kind cannot be foretold with 

 much certainty from the results of chemical analyses as it 

 has been the custom to make and present them. It has 

 been found, for example, in the arid west, that soils nota- 

 bly deficient in humic nitrogen and which for this reason 

 should be comparatively unproductive, have, nevertheless, 

 been found capable of giving large yields when irrigated. 

 Then again, in moist climates there are types of soil ex- 

 ceptionally rich in both humic and nitric nitrogen which 

 are comparatively unproductive until they are given 

 dressings of coarse farmyard manure. The analyst would 

 place them among the richest of soils and yet they are 

 among the poorest until given farmyard manure; and, 

 what appears stranger still, straw and coarse litter may 

 be much more beneficial to them than liquids from the sta- 

 ble cistern. 



79. Essential Constituents of a Fertile Soil. While it is 

 true that our chemical knowledge of soils is very unsatis- 

 factory, it has nevertheless been thoroughly established that 

 a fertile soil must contain certain substances in order to 

 permit any crop to come to maturity upon it and these are 

 potassium, calcium, magnesium, phosphorus, sulphur, iron, 

 nitrogen and probably chlorine. Let any one of these ele- 

 ments be absent from a soil, or its moisture, and crops fail 

 to develop upon it. It has not, however, been established yet 

 in what form of combination these elements must or may 

 exist nor in what proportions to give the best results. It 

 is known that they do not exist in the soil in the elementary 

 form and that they are combined in a great variety of ways. 



