214 Bureau of Farmers' Institutes. 



soil, owing, in part to the different condition in which the mineral 

 food exists in the sandy soil. The insoluble condition of plant 

 food in the soil prevents its rapid loss by leaching. 



Loss of Fertilizing Constituents from the Soil. — Without go- 

 ing into a detailed explanation in regard to the causes, we will 

 consider briefly the extent to which the three chief forms of 

 plant food are liable to be lost from soils. In general, it may be 

 said that when plant food materials come into contact with a 

 soil, some kind of chemical combination is apt to take place be- 

 tween the constituents of the soil and the fertilizer. On this 

 account, plant food when applied in soluble forms may combine 

 with the soil to form compounds which are less soluble, but still 

 sufficiently soluble to be utilized as food by plants. 



(a) Nitrogen Compounds. — Since ammonia compounds and ni- 

 trates dissolve easily in water, is there not danger of their being 

 carried away in drainage water from the upper soil out of reach 

 of the plants ? Experiments have been made to settle the question, 

 and results indicate that ammonia compounds are largely retained 

 until they are changed into nitrates. Nitrates are apt to be washed 

 out in drainage water and lost in the case of bare fallow land, 

 the loss amounting to nearly 40 pounds of nitrogen an acre in 

 average seasons. The quantity of nitrogen lost in this way is 

 very much greater than is used by many crops, and is, moreover, 

 in the most available form for plant food. However, when soil 

 is covered with vegetation there is little or no loss, for the 

 reason that roots of growing plants absorb nitrate nitrogen very 

 rapidly. 



Some nitrogen may be lost also from organic matter undergo- 

 ing decay in the soil, escaping into the air as free nitrogen. This 

 has been shown to be very large in case of soils rich in vegetable 

 matter when improperly managed. 



(&) Phosphoric Acid in Phosphates. — The ordinary form of 

 calcium phosphate being insoluble in water, is not, to any appreci- 

 able extent, removed from the soil by the drainage water. The 

 soluble form of calcium phosphate would probably be lost to 

 some extent in drainage water, were it not for the fact that it 

 is quickly changed in the soil to the " reverted " or less soluble 

 form and, in this " reverted " condition, the phosphate is not 

 apt to be carried away in drainage water. In some soils, heavy 

 clay soils, for example, soluble phosphates not used the first 



