38 THE ELEMENTS AND THE SOIL 



of a field commodious and sanitary, and at the same time to maintain 

 within it a sufficiently rapid development of readily water-soluble 

 plant-food materials so conditioned as to be highly available to the crop, 

 requires careful attention to many essential details. Some of the chief 

 objects of tillage are : 



(1) To secure a thorough surface uniformity of the field, so that an 

 equally vigorous growth may take place over the entire area. 



(2) To develop and maintain a large effective depth of soil, so that 

 there shall be ample living room, an extensive feeding surface and large 

 storage capacity for moisture and available plant-food materials. 



(3) To increase the humus of the soil through a deep and extensive 

 incorporation of organic matter, so that there may be a strong growth 

 of soil micro-organisms and the maintenance of a high content of 

 water-soluble plant-food materials. 



(4) To improve the tilth and maintain the best structural condition 

 in the soil, so that the roots of the crop and the soil organisms may 

 spread readily and widely to place themselves in the closest contact 

 with the largest amount of food materials. 



(5) To control the amount, to regulate the movement, and to deter- 

 mine the availability of soil moisture, so that there shall never be an 

 excess or a deficiency of this indispensable carrier of food materials 

 to and through the plant. 



(6) To determine the amount, movement, and availability of the 

 water-soluble plant-food materials present in the soil, so that growth 

 may be both rapid, normal, and continuous to the end of the 

 season. 



(7) To convert the entire root zone of the soil into a commodious 

 sanitary living and feeding place, perfectly adapted to the needs of the 

 roots of the crop and to the soil organisms, adequately drained, 

 perfectly ventilated, and sufficiently warm. 



(8) To reduce the waste of plant-food materials through the de- 

 struction of weeds, and the prevention of their growth, through preven- 

 tion of surface washing and drifting by winds. 



Jordan's rules of fertility. 



1. Thorough tillage, with efficient machinery, to be given if possible 

 when the moisture conditions of the soil admit of satisfactory pulveri- 

 zation. 



