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ENCY(.'L01'K1)1A OK I'UAt'TU'AL HOKTU'IILTIIIUO 



of elements is taken up by llie iiUuU rool 

 hairs in contact with the soil particles 

 and serves as plant food. If we continued 

 to pour water through our bucket of soil 

 we should soon discover that we had prac- 

 tically exhausted the soluble material in 

 the soil. Kxaniination of the soil from a 

 vi.corous growing, well cultivated crop in 

 .luly or August would also show that the 

 Immediately soluble material in the soil 

 would supply the growing plants only a 

 few weeks at best — not nearly enough to 

 last through the growing season. 



How. then, is the growing plant to be 

 kept in food? If the bucket of soil from 

 which you washed practically all the sol- 

 uble material be set aside for a few days 

 and be kept nicely moist it will be found 

 you are again able to dissolve consider- 

 able material from the soil. Certain 

 chemical changes have been going on in 

 the bucket of soil that have changed a 

 small amount of the insoluble material 

 into soluble form. These same chemical 

 changes take place in the field under suit- 

 able conditions, but the rapidity of the 

 changes will vary markedly with varia- 

 tions in the necessary conditions. 



The secret of successful soil manage- 

 ment rests in keeping (he conditions right 

 for the liberation of as much food as a 

 bumper crop can use — no more, no less. 



If the soil is managed so that consid- 

 erably more of the imiiortant elements 

 are made soluble than the crop can use, 

 the surplus will be washed away to a 

 large extent and the soil will be rai)idly 

 depleted of its latent or reserve fertility. 

 If less than enough to support a maximum 

 crop is made available, the legitimate 

 profits of soil tillage are directly reduced, 

 or, as is true in many cases, the receipts 

 do not pay the cost of operation. 



Xecessarj' Conditions — .\ir 



1. The proper circulation of air in the 

 soil. Oxygen of the air helps to break 

 down the hard rock material In the soil 

 much as it changes the hard, shiny sur- 

 face of a plowshare to a powder frust) in 

 the presence of moisture. Without 

 oxygen plant roots will die. Oxygen 

 taken in by the leaves will not take the 

 place of oxygen needed by the roots. 



Many of the desirable chemical changes 



in the soil are due to the action of soil 



bacteria with which all healthy soils are 



teeming. These bacteria cannot thrive 



without oxygen. .lust to the, extent that 



the full amount needed is reduced will 



the desirable bacterial action be reduced. 



There cannot be proper circulation of air 



in a soil well filled with stagnant water, 



nor can there be proper circulation of air 



in a field packed hard and dried into 



brick-like clods. We recognize by the 



growth on such soils that something is 



wrong. 



Humus 



2. A good supply of organic matter. 

 This furnishes food for soil bacteria. 

 Through their action the organic matter 

 decomposes, and weak acids are formed, 

 which attack and dissolve the rock ma- 

 terial, putting it into available form for 

 the plants. With a deficiency in organic 

 matter there will not be enough acids 

 I'ornied to liberate the desired amount of 

 mineral elements. A variation in the 

 amount and rapidity of decomposition of 

 the organic matter will also cause corre- 

 sponding vai'iation in the supply of avail- 

 able nitrogen for the i)lant. Deficiency 

 of nitrogen and need for more organic 

 matter is readily recognized by the light 

 yellowish color of growing vegetation, 

 while an abundant supply is recognized 

 by the rich, dark-green, luxuriant foliage. 

 Note difference in color after the applica- 

 tion of barnyard manure or the plowing 

 under of a clover sod. 



The organic matter makes heavy soils 

 more friable and easy to work, and less 

 likely to puddle and bake, and opens 

 them up so they will take water and air 

 lietter. It partially fills the pores of loose, 

 sandy and gravelly soils, making them 

 more compact, increasing their power to 

 hold water and soluble plant food, les- 

 sening the danger in a wet climate, or, 

 under irrigation, of leaching away of 

 available plant food. 



Moisture 



3. A pro|)er supi)ly of capillary mois- 

 ture. Water alone has a very gradual 

 solvent action on the rock material, but 

 it is as essential in keeping up healthy 

 bacterial action in the soil as it is to a 



