190 STATE HORTICULTUEAL SOCIETY. 



The three elements of plant food most ofcen depleted by contin- 

 ued cultivation and the removal of crops are potash, nitrogen and 

 phosphoric acid. Unless this process of depletion has been carried 

 too far, or unless the soil was naturally thin and weak, a season of rest 

 will render this soil again fairly productive for a short time, inasmuch 

 as a portion of the plant food yet contained in this soil is made soluble 

 and accumulates there. By this process, however, nothing is added to 

 to the soil, and the supply of plant food already there is drawn upon 

 in the most expensive manner. 



An application of barnyard manure, or the plowing under of a 

 crop of clover or cow-peas will produce the same effect as the summer 

 fallow or rest, and further improve the soil in the following ways : 



1. It adds a supply of readily available plant food upon which 

 the trees and succeeding crops can feed at once. 



2. It is well known that the vegetable manures of this class serve 

 other equally important purposes in the soil, otherwise many strawy 

 stable manures, from the application of which good effects may be 

 seen for several years, would not be worth hauling to the field and 

 spreading. That is to say, the potash, nitrogen and phosphoric acid 

 contained in them could have been purchased and applied in the form 

 of commercial fertilizers for less expense than the hauling and spread' 

 ing of these manures would amount to. Then, by the addition of this 

 vegetable matter, the physical condition of the soil has been improved ; 

 it is made more friable, more easily tilled ; its water-holding capacity 

 has been greatly increased, at the same time that its capacity for ab- 

 sorbing the water which falls on its surface in the form of rain, snow 

 and dew is increased. An example of the difference in water-holding 

 power of soils, due alone to a difference in the amount of vegetable 

 matter, is reported in a recent Experiment Station bulletin as follows : 



New soil, cultivated two years, contained 3.75 per cent of vege- 

 table matter, and contained at the time the samples were drawn 16.48 

 per cent of water. A similar soil adjoining, which had been culti- 

 vated until the vegetable matter had been reduced to 2,50 per cent, 

 contained at this time only 12.14 per cent of water. This means a 

 difference of 1 | quarts per cubic foot of soil. Other cases are re- 

 ported in \«hich the soils with a normal amount of vegetable matter 

 contained more than one-fourth more water than those in which this 

 material had been burned out by cultivation. 



Not only do the soils containing the larger amount of vegetable 

 matter contain more water, but this water is given off more slowly by 

 evaporation. An experiment with the two soils above described in 

 which they were subjected to the sime temperature, having been wet 



