GRAYLING INSTITUTE. 321 



an absolutely large amount to the acre. If we call the weight of an acre of 

 soil one foot deep, four million pounds, we see that .06 percent, of magnesia, 

 (Hanna) means 2,400 pounds to the acre, enough for a full wheat crop for 

 300 years. A soil that holds only a fraction of a per cent, of some chemical 

 of plant growth may still contaiu an immense store of plant food. 



A soil that has a relatively high percentage of lime, potash, phosphoric 

 acid and combined nitrogen usually shows a high degree of productiveness. 

 But as Hilgard has shown, it does not follow that low percentages necessarily 

 show low production. A heavy alluvial soil of high percentage of ash ingre- 

 dients will produce a maximum crop under favorable climatic conditions. If 

 we add to Lhis soil an equal weight of clean sand, thereby reducing the ash 

 percentage one-half, the crop will not be reduced one-half, but may still pro- 

 duce a maximum crop on account of the improved physical condition of the 

 soil. In open and porous soils the roots of plants will be longer and better 

 developed, will penetrate the whole mass of the soil and thus reach and appro- 

 priate as much food as in the rich but compact soil. A relatively low per- 

 centage in quick soils will produce as good crops as a high percentage in slow 

 soils. 



Let me now call your attention to each of the chemicals found in soil 

 analysis. 



Oxide of iron. — The amount of oxide of iron in the ash of crops is very 

 small. A few pounds at the most will cover the year's expenditure in the 

 crop on each acre of soil. While this amount is indispensable for the growth 

 of the crop, this does not measure the whole value of oxide of iron in the soil. 

 Practical men recognize the fact that red land is better than white soil. 

 Compare these soils from the plains with the sand from New Jersey pine bar- 

 rens. The singular powers of oxide of iron to take up and hold in soluble 

 form potash, ammonia and phosphoric acid, and thus to prevent leaching of 

 manures, and to retain moisture, and thus resist drought, are most valuable 

 qualities in the soil. Yet oxide of iron tends to dissipate vegetable matter in 

 the soil, and soils rich in oxide of iron must be carefully managed to accumu- 

 late humus. The abundant supply of oxide of iron in all the soils of the 

 plains is a favorable indication. 



Lime. — In the agriculture of the old world lime is held in high estima- 

 tion, the British farmer using it in large doses. In the dryer climate of the 

 United States, France and Germany, lime is used in smaller quantity, which 

 seems to be as efficacious as the large doses in Great Britain. 



In the fifth volume of U. S. census, 1880, Hilgard states that the lightest 

 sand should not contain less than .10 per cent of lime, clay loam not less than 

 .25 per cent, and heavy clay not less than .50 per cent, and that this percent- 

 age may advantageously rise to 1 or 2 per cent, but no increase beyond this 

 amount seems to have any chemical benefit, but only to mechanically improve 

 the soil. 



By reference to the table of analyses you will see that the soil of the plains 

 contains from three to five times the lowest limit allowed by Hilgard to light 

 sands. Yet I have no doubt that these lands would be benefited by a liberal 

 dose of lime, and the beds of marl scattered through this region give a hint 

 not to be neglected. 



The beneficial influence of lime in agriculture is very marked : It pro- 

 motes the oxidation of organic matter of the soil and formation of nitrates; 

 prevents the prongy growth of root crops or "fingers and toes" of turnips 



41 



