No. 6. DEPARTMENT OF AGRICULTURE. 631 



the liquid will rise. The amount of water then that a soil will hold 

 depends, primarily, on the size of the soil particles. The amount of 

 organic matter present in any soil materially effects its water-hold- 

 ing capacity. The more humus present, the more water held. The 

 humus content, however, may be so excessive that too great a supply 

 of water is held, as in the case of peaty soils. 



In this matter of moisture, we seek for a medium amount, too 

 much or too little being detrimental. When gravitational water 

 fills all of the pore space, we have no room for the much needed 

 oxygen, a point that will be considered later. 



The temperature of a soil naturally effects the growth of crops. 

 It is well known that certain temperatures are required for germi- 

 nation. There is a maximum and a minimum temperature between 

 which all plant life must be kept, in order to secure growth. These 

 temperatures range from 41 degrees to 115 degrees F., with the 

 best average growth at about 85 degrees F. If, therefore, the 

 farmer is able to help nature keep an average soil temperature, he 

 has very materially aided in crop production. A wet soil is natu- 

 rally a cool soil. If too much drainage water be present, we may 

 increase the temperature by land drainage. Farm manure and 

 other decaying organic matter, by the action of fermentation, sets 

 up a heating effect which is instrumental in warming the soil. Farm 

 manure, therefore, has a secondarv effect other than that of a fer- 

 tilizer. It is found also that tillage helps to warm the soil, allow- 

 ing the warm air to circulate among the soil particles. This, then, 

 is another factor that may be aided by the farmer. 



Plant roots must secure oxygen or the plant cannot live. The 

 oxygen is supplied by the air in the soil. A soil that is so packed 

 that but little pore space remains, or whose pore space is filled 

 with drainage water, cannot possibly be productive. The first con- 

 dition may be benefited by tillage, by a loosing up of the soil parti- 

 cles, so that air may enter. The second is helped by draining, re- 

 moving the surplus water, thereby allowing aeration to proceed. 



The question of tillage is probably one of the most important 

 factors that farmers have to deal with. As we have seen, tillage is 

 useful in controlling the moisture, the temperature and the circula- 

 tion of air in the soil. Working over the surface layers forms a 

 mulch which breaks up the capillary spaces, thereby conserving the 

 moisture. By stirring the soil we increase the pore space near the 

 surface, thus making the passage of the air more pronounced, in 

 creasing thereby the soil temperature and supplying the vital ele- 

 ment, oxygen. 



The question of soil fertility is indeed an important one and is 

 well worthy of our eousideration. Of the ten elements used by the 

 plant as food, but three, with possibly a fourth, are liable to exhaus 

 tion. These are nitrogen, phosphorus, potassium and lime. The 

 question of soil fertility from a chemical point of view resolves itself 

 into the supplying of these elements to the soil. We must not lose 

 sight of the physical properties, for by their action the availability 

 of our fertility constituents is largely controlled. Crops, when re- 

 moved from the land carry varying amounts of plant food. One 

 hundred bushels of corn for example contains 100 pounds of nitro 

 gen, 17 pounds of phosphorus, and 19 pounds of potassium. Seventy- 

 five bushels of oats contains 45 pounds of nitrogen, 7 pounds of 



