468 STATE BOARD OF AGRICULTURE. 



addition the soil must be ventilated in some cases to keep up the sup- 

 ply of nitrogen. 



Seeds will not germinate in the absence of oxygen. Plants not only 

 will not grow when their roots are not supplied with oxygen, but will 

 actually die because of its absence. The nitri tiers (the organisms in the 

 soil that transform the nitrogen of the organic matter into nitric acid, 

 which is so essential for the support of our domestic plants) cannot 

 carry on their work in the absence of oxygen. 



On the other hand there is another class of organisms found in the 

 soil, which, when oxygen is absent from the soil, will destroy those forms 

 of nitrogen which have been prepared or are in process of preparation 

 for our domestic plants. These organisms have been known to destroy 

 as much as six hundred pounds of potassium nitrate per acre in three 

 weeks in a water-logged soil. These organisms are known as denitri- 

 fiers. 



Free nitrogen fixers, the organisms found in the nodules on the roots 

 of clovers, beans, peas, and other legumes, take the free nitrogen of the 

 air in the soil and combine it with oxygen and hydrogen to form nitric 

 acid. These organisms must have the supply of nitrogen provided with 

 which to work, and must be supplied with oxygen to assist them in carry- 

 ing on tbeir work. Two much water in the soil excludes the air. 



The roots of ordinary crops cannot grow under water. Under best 

 conditions the roots of com plants will grow to a depth of ten to fifteen 

 or more feet. The roots of oats will grow to a depth of six to ten or 

 more feet, as will also the roots of clover. If, therefore, water stands 

 within three feet of the surface of the ground when the root systems of 

 these crops are developing, the area which these roots may occupy is 

 much restrictei]. 



Soil puddles, or ''bakes.'" when water is allowed to stand in or upon 

 it. This puddling helps to exclude the air and at the same time ofifers 

 resistance to the development of the root systems of plants. It lessens 

 the power of the soil to hold water useful to plants and at the same time 

 increases the tendency to loss by evaporation. Puddled soils crack in 

 drying and thus again restrict root development, or in case roots are 

 already occupying the soil, the roots are broken. 



Ordinarily a soil that is properly drained and properly tilled becomes 

 sufficiently mellow to a proper depth to permit the most complete de- 

 velopment of the root systems of our crops. Because it is mellow its 

 capacity for moisture in proper condition for the use of plants is greatly 

 increased, so that, paradoxical as it may seem at first thought, a well 

 drained soil will, in dry weather, produce a much better crop than will 

 an undrained soil of the same type. 



LAXDS LIKELY TO NEEH DRAINAGE. 



1. Low lying flat areas, and especially those more or less surrounded 

 by hills. 



2. Higher areas of open soils with comparatively slight slopes and 

 underlaid by rather imperious sub-soils. 



3. Heavy clay soils even though they have apparently considerable 

 natural surface drainage, but more especially when the surface is marked 

 by slight depressions, from which the water cannot drain readily. 



4. It frequently happens that in regions generally well drained there 



