160 



SCIENCU. 



[Vol. VIII., No. 185 



phosphoric acid, $418,865,930 ; nitrogen, |2,326,- 

 852,674 ; total. $3,343,786,050. 



These quantities of plant food removed from 

 the soil annually seem enormous, but it must be 

 remembered that they are not all lost : much of 

 them is left in the soil in roots, straw, stalks, etc. 

 Those, however, who are acquainted with the 

 method of farming practised in the newer parts 

 of our country know that corn-stalks and straw 

 are generally regarded as nuisances, to be removed 

 as easily and speedily as possible. It is not tilling 

 but killing the soil that is practised. Stables are 

 removed to get out of the way of the accumulat- 

 ing manure, and the corn-stalks are raked togeth- 

 er and burned to prepare the field for a new crop. 

 True, in many localities the waste of such a pro- 

 ceeding, especially in nitrogen, is understood. 

 Yet it must be confessed that over vast areas of 

 our agricultural lands there is no conception of 

 the idea of possible exhaustion of the soil, and no 

 systematic method of preventing it. The refuse 

 of the crop, the straw, the stalks, etc., are put out 

 of the way as easUy and quickly as possible, and 

 without thinking of the robbery which is thereby 

 committed. The stores of plant food which have 

 accumulated in our virgin soils are indeed great, 

 biit they cannot withstand this constant drain on 

 them. The effects of this system of culture soon 

 show themselves in diminished yield, as is seen in 

 the great wheat fields of the north-west and of 

 California, which do not produce at the present 

 time more than half the crop at first obtained 

 from them. 



If we place at 40 pounds the annual contribu- 

 tion of potash of an acre of land to the crop, the 

 number of crops which could be produced in a 

 given depth, as far as this constituent of soil is 

 concerned, is easily computed. The weight of dry 

 soil per acre to a depth of nine inches is approxi- 

 mately 3,000,000 pounds. A soil containing .3 per 

 cent of potash would have, therefore, 9,000 pounds, 

 which, at 40 pounds a year, would last for 250 

 years. But fortunately, by the decomposition of 

 feldspathic rocks and others containing potash, 

 and also by the ti-ansfer in various ways of the 

 subsoil to the soil, a provision is found which will 

 prevent the entire exhaustion of the soil. Thus it 

 happens, that, in many parts of the world where 

 fields have been under cultivation for hundreds of 

 years, there is still a sufficient amount of this 

 manurial substance to insure the production of a 

 crop. 



Further, it must not be forgotten that there are 

 many manurial substances containing potash 

 which are accessible, and which will furnish im- 

 mense stores of this substance to the future agri- 

 culturist. Chief among these natural deposits 



must be mentioned the mines of kainit, which 

 have their greatest development near Stassfurt. 

 These mines have already furnished immense 

 quantities of potash, and there is no immediate 

 danger of their exhaustion. 



The available quantity of phosphorus as plant- 

 food may be estimated in the same way. The 

 quantity of phosphoric acid in soils varies from 

 none at all to almost one per cent. If we take 

 the mean content of phosphoric acid in a soil to 

 be .15 per cent, the total quantity per acre to a 

 depth of nine inches would be 4,500 pounds. If 

 the contribution to each crop is 20 pounds per 

 acre, the phosphoric acid would last for 225 years 

 without any artificial supply. 



The stores of phosphoric acid, however, which 

 a provident past has saved for us, are even greater 

 than the deposits of potash. Apatite is a some- 

 what abundant mineral ; and in South Carolina 

 and Alabama, and other states of the union, are 

 found large beds of phosphates. Some idea may 

 be formed of the extent of these deposits by study- 

 ing the dinoensions of the largest bed of them yet 

 discovered, having its centre at Charleston, S. C. 

 This bed has been traced for a distance of 70 miles 

 parallel with the coast, and has a maximum width 

 of 30 miles. In view of the fact that only prelim- 

 inary surveys have been made of the phosphatic 

 beds in North Carolina, Alabama, and Florida, 

 and that these suiweys have shown the presence 

 of immense quantities of these deposits, it is just 

 to conclude that the mineral wealth of the coun- 

 try, in this particular, is of no mean proportions. 



The quantity of phosphates imported into the 

 United States (not including guano) has dimin- 

 ished with the increase of home production, having 

 fallen from 133,955 tons, worth $1,437,442, in 1888, 

 to 27,506 tons, worth $367,333, in 1885. 



For the fiscal year ending June 30, 1885, there 

 was exported from the United States farm pro- 

 ducts having a value of $530,172,835. The value 

 of agricultural products imported was $249,211,- 

 975, more than half of which %vas sugar, tea, and 

 coffee. The excess of exports over imports was 

 therefore $280,960,860. 



It must be remembered, however, that the values 

 of exports are given at the seaboard, and are fully 

 25 per cent greater than for the values given at 

 the farm. To compare, therefore, exports with 

 total production, the sum above given must be di- 

 minished by one-fourth, becoming $397,629,626, or 

 11 per cent of the total net value of the farm pro- 

 duction of the country. Allowing for the small 

 quantities of valuable plant-food introduced in our 

 agricultural imports, we may safely place the loss 

 of these ingredients, due to exportation, at 10 per 

 cent of the whole. 



