90 CHEMISTRY OF FARM PRACTICE 



can readily be seen that a young and growing animal will 

 remove considerably more plant food and use it in the 

 elaboration of tissue than will a mature animal. Another 

 factor influencing the composition of the manure will be 

 the composition of the feed. The third factor, which is 

 probably the most important of all, is the care of the 

 manure. If, after carefully considering his own conditions, 

 the farmer decides that it is more profitable for him to 

 feed the crop and return the manure to the land, which 

 is usually the decision reached in diversified farming, there 

 are several factors still to be considered; these will be 

 discussed in the following chapter. 



68. Keeping the Land Covered. Under the prevailing 

 methods of crop growth, the land is allowed to lie bare a 

 part of the year. During this time, especially if the weather 

 is warm, there is some nitrification going on, and much 

 plant food is lost through leaching. It is good practice 

 to keep a growing crop on the land as much as possible, 

 to take up the plant food as it becomes available and con- 

 vert it into an organic form. If such a crop is planted as 

 a winter protection to the soil, it is known as a cover crop. 

 The cover crop is a material aid in the prevention of 

 washing, because it fills the soil with fibrous roots which 

 tend to hold the soil together. When a crop is planted 

 between two other crops, it is known as a catch crop. An 

 example is the planting of cowpeas or soy beans after 

 grain has been harvested and before another grain crop is 

 planted. 



When leguminous plants can be used for cover or catch 

 crops, or in connection with other crops used for this pur- 

 pose, they serve another purpose; that of collecting nitro- 

 gen from the atmosphere and storing it in such a form 

 that it is available as plant food. A more general use of 

 cover crops and catch crops, especially of the legumes, 

 will mark a great step forward in our agricultural devel- 

 opment. For cover crops, clovers, vetch, oats, and rye 



