GRAYLING INSTITUTE. 323 



per cent must be regarded as seriously deficient unless accompanied by a large 

 amount of lime. 



By reference to the table of analyses you will see that all the soils of the 

 plains rise above Hilgard's minimum, the average being .086 per cent, while 

 the Campine sands of Belgium fall much below (.031). 



The agricultural powers of these soils would be greatly increased by an 

 increased supply of available phosphoric acid This may be be done by the 

 use of commercial superphosphates. To get a satisfactory system of rotation 

 of crops established, to get the soil, so to speak, on its feet and in a condi- 

 tion to help itself, these commercial fertilizers may play an important part, 

 but the true policy is to make the soils self-supporting agriculturally, not fed 

 or stimulated by imported supplies. I will call your attention to this sub- 

 ject before I close. 



Organic matter or humus of the soil is a material of great importance in 

 agriculture both from its physical properties in relation to heat moisture and 

 texture of the soil, and because it is directly and indirectly the storehouse of 

 combined nitrogen for plant growth. 



In 1868 it was shown by a set of experiments on the temperature of soils, 

 extending from the first of May to the first of October, that soils containing 

 twelve per cent of organic matter are warmer by one and a half to two and a 

 half degrees Fah. than similar soils destitute of organic matter. During 

 every month of active growth the soils rich in organic matter maintained an 

 average temperature much above that of similar soils under like exposure, 

 but destitute of humus. This was no mere laboratory experiment, for the 

 soils were exposed under agricultural conditions in the open field. 



Many persons have observed that dark soils warm up quicker than light 

 colored soils when exposed to the sun's rays. But humus does more than 

 this ; the soil not only warms up quicker but stays hot longer than soils des- 

 titute of organic matter. It is not only hotter at midday but warmer at bed 

 time. 



No other substance in the soil has such power to combine with and retain 

 water as humus. It holds the rain, prevents its rapid drainage, and stores it 

 up for time of need. Its influence in preventing or mitigating drought is of 

 great importance in quick soils. 



If you refer to the table of analyses you will find at the close of each a line 

 that reads : "Capacity to hold water — per cent." This requires a word of 

 explanation. If 100 parts of dry soil are weighed out, and water is poured 

 upon this until the soil has taken up all the water it will absorb and hold, 

 the amount of water thus taken up measures the capacity of the soil to hold 

 water. This is done in each case for 100 parts of soil, and thus the capacity 

 is measured per cent. This power of the soil to drink in and hold the water 

 depends upon the fineness of division of the soil and the amount of organic 

 matter. It measures the power of the soil to resist drought. In some very 

 rich soils in this State I have found the capacity to hold water to range from 

 fifty to seventy per cent, that is, one hundred parts of such dry soil would 

 take up and hold in capillary form from fifty to seventy parts of water. Such 

 soils contain from seven to twelve per cent of organic matter. On the other 

 hand the sand from pine barrens of New Jersey will hold only twenty-five 

 per cent of water. The soil from the plains ranges from thirty-one to thirty- 

 six per cent. They should be brought up to a capacity of forty, which can 

 only be done by increasing the amount of humus in the soil. 



