56 Effective Farming 



stable manures, the growing of green-manure crops. We 

 consider here what may be called the home practices and sup- 

 plies. To supply humus is one of the great necessities in 

 farming, as well as to add directly to the plant-food content 

 of the soil. The element of conservation, or saving, is also 

 very important, for we cannot make headway if we neglect 

 or waste the materials produced on the farm. The soil and 

 the live-stock can utilize most of the wastes and the materials 

 not sent directly to the market or used as food for human 

 beings and animals. 



26. The food elements of plants. In order that normal 

 crops may be produced, all of the food elements to be taken 

 up by the plants must be present in the soil and in an available 

 form to be absorbed by the roots. Investigation has shown 

 that only three of these elements in the soil, nitrogen, phos- 

 phorus, and potassium, are likely to be low in amount. A 

 study of these elements, therefore, is of importance to farmers, 

 for if any one of them becomes deficient, profitable crop 

 production cannot possibly continue on that soil. These 

 three elements are contained in fertilizers and barnyard ma- 

 nure. They are among the foods taken up by plants from the 

 soil; consequently, whenever weeds, stubble, or crops grown 

 for the purpose are turned underneath the furrow-slice, the 

 food in the plants is returned to the soil. 



Nitrogen, phosphorus, and potassium. Nitrogen is usually 

 taken up by plants in the nitrate form. Plants like rice that 

 grow on soil covered with water can utilize ammonia. It has 

 recently been shown, too, that some crops use nitrogenous or- 

 ganic matter. Phosphorus and potassium are found in soil in 

 mineral compounds. Many of these are almost insoluble, but 

 they change slowly into soluble compounds, thus becoming 

 available as plant-food. 



Unfortunately there is no uniformity in the terms used to 

 express the nitrogen, phosphorus, and potassium content of 

 soils, manures, and fertilizers. In some instances the names 



