CHEMISTRY AND CROPS. 163 



val of time. This is the chief problem that presses for solution 

 in countries that are yet only sparsely settled. In buying- a housf 

 one takes into account its probable life and cost of upkeep ; so, 

 also, in buying a farm one should be able to ascertain how long: 

 the soil will continue to produce good crops, and what will there- 

 after be the probable cost in fertilisers necessary to maintain 

 its production. This depends primarily upon the quality of the 

 soil, viz., on its chemical and physical characteristics. So im- 

 portant a point is soil quality that Dr. Wm. MacDonald,* ir 

 reducing the various points of a farm to the score card, gives it 

 no less than 20 per cent, of the total marks, and no doubt if it 

 were not for the fact that proximity to railway and market makes 

 fertilisation a practical undertaking, the number of marks so 

 assigned would have figured very much higher. It is this second 

 problem, this ascertainment of the permanent productive capacity 

 of virgin soils, which is of especial importance to South Africa, 

 for most of our land is yet in its virgin state. Let us now see 

 how far chemistry is able to help us in its solution. 



If the various states in which plant food occurs in soils be 

 considered it will be found that there is a water-soluble portion, 

 a zeolitic store and a yet unearthed mineral reserve. Under the 

 influence of the natural agencies the mineral reserve is daily 

 contributing to the production of the water-soluble and zeolitic 

 stores, both of which are readily available to the plant, especially 

 the former. It is evident that cropping, and perhaps drainage, 

 will continually reduce the water-soluble and zeolitic forms ; but 

 the rapidity with which this occurs will depend on the rate of 

 transformation of the mineral reserve. This rate will evidently 

 depend upon the activities of the natural agencies, and also to a 

 greater degree upon the amount of and the fineness of grain of 

 the unweathered mineral particles. Further, it follows that given 

 similar conditions, the greater the original amount of the mineral 

 reserve in a soil the larger will be the stores of zeolitic and water- 

 soluble forms at any subsequent date. If this be accepted, it 

 must also follow that virgin soils which show high percentage 

 of plant food materials are bound to be fertile, and lastingly so. 

 Therefore the problem the chemist has to solve in dealing with 

 the permanent productivity of a virgin soil is one of findmg a 

 solvent that will dissolve a maximum amount of all three forms 

 of plant food materials. Such solvents are nitric and hvdrochloric 

 acids. The advantages of the latter acid are so numerous that 

 there is no need for me to mention them here. It is the one 

 that has been used bv Hilgard and Loughridge in America for 

 the past 40 years with distinct success. Hilgard f writes of th.- 

 method as follows : 



"It seems to be generallv true that virgin soils showing high 

 percentages of plant food as ascertained bv extraction with strong acids 

 invariably prove highlv productive ; provided only that extreme physical 

 characters do not interfere ^vith nominal plant growth as is sometimes 

 the case with heavy clays, or very coarse, sandy lands, io ttiis lule 

 no exception has thus far been found." ^ ^ 



*Spe Transvaal Agricultural Tournal. 

 +E. W. Hilgard : "Soils: their formation, properties, etc."p. 343 



