lo Sept., 191 2.] W'lieat and its Ctdtivailon. 543 



WHEAT AND ITS CULTIVATION. 



{Continued from page 465.) 



Xo. 7.— MANURIAL PROBLEMS. 



A. E. V . Rich nd son, M.A., B.Sc, Agricultural Superintendent. 



It has already been demonstrated that the most important requirement 

 of a permanent system of agriculture is the maintenance of the productive 

 power of the soil, and that the permanent efficiency of any given method 

 of cultivation must be determined by its effect on soil fertility. 



Under a good system of farming the soil will gradually increase iif 

 productive power. Poor soils may be improved and rich soils made richer. 



Bad methods of cultivation, however, will gradually deplete the soil 

 of its fertility, and render rich soils incapable of producing other than 

 mediocre crops. 



Factors Involved in Soil Fertility. 



Soil fertility, in practical language, is the cropping capacity — the pro- 

 ductive power — of the soil. It is a complex of many factors — some external 

 -^some internal. 



Obviously, the climate is the most important external factor, and the 

 amount of rainfall, its seasonable distribution, the range of temperature, 

 &.C., are controlling influences in successful farming. Excluding these 

 climatic considerations, however, as entirely beyond human control, we 

 may say that the fertility of a soil is dependent on the chemical, physical , 

 and biological nature of the soil. Let us consider these points seriatim. 



Chemical Composition. — One of the most common characteristics of a 

 fertile soil is that it contains, in a soluble or available form, a sufficiency 

 of those elements necessary for the nutrition of plants. These are ten in 

 number fp. 200), namely, carbon, hydrogen, oxygen, nitrogen, sulphur, 

 phosphorus, potassium, iron, magnesium, calcium (lime). The first three 

 are obtained from the air and water, the remaining seven are obtained 

 from the soil. 



All these elements are essential plant foods. Fortunately, seven of 

 these ten essential constituents are present in most soils in overflowing 

 quantities. The other three— nitrogen, phosphorus, and potash — are 

 frequently wanting or deficient. As the yield of the crop is governed 

 by the amount of the most deficient element present, it is obvious that 

 a study of the three substances referred to is of immediate practical 

 importance. Lime sometimes becomes of considerable practical importance 

 in assisting production, but the necessity for lime invariably arises from 

 a faultv physical and biological condition of the soil, and not because 

 it is actually required for plant food. 



In the case of the wheat crop (straw and grain), of the to'al amount 

 of food taken in by the crop^ — 



(i) No less than 93^ per cent, is obtained from the air and from 



the rain. 

 (-) 3l P^r cent, consists of mineral substances with which the .soil 



is abundantly supplied. 

 (3) About 3 per cent, consists of nitrogen, phosphoric acid, and 

 potash, which the soil contains in strictly limited quantities. 

 Hence, that portion of the plant's needs which man may require to supplv 

 is only a small fraction of that which is yielded by crops. But it is an 



