DETERMINING THE LOSSES AND GAINS 351 



of the soil supply of the important plant-food elements may be 

 briefly summarized as follows: 



How losses occur: 



(a) In the sale of crops 



(6) In the feeding transaction. 



(c) Leaching from the soil nitrogen particularly 



(d) Soil erosion 

 Sources of gain: 



(a) Feeds purchased 

 (6) Fertilizers purchased 



(c) Nitrogen fixation, especially by legume bacteria 7 



(d) Bedding purchased, particularly straw 8 



Determining the Losses and Gains. When the manure pro- 

 duced is well cared for and all straw and other material like clover 

 chaff and uneaten shredded corn stalks are passed into the manure 

 as bedding, the approximate losses and gains of the plant-food 

 elements, particularly nitrogen and phosphorus, may be ascer- 

 tained. In constructing the balance sheet, the following rules 

 should be observed : 



1. The amount of nitrogen, phosphorus and potassium con- 

 tained in any crop sold, except the nitrogen in legumes sold, is to 

 be considered lost to the soil on the farm. (Consult the composition 

 table, Chapter VI, and also the table on page 393, for the 

 amount of the fertilizing elements contained in crops and feeds.) 



2. Losses sustained in the feeding transaction may approxi- 

 mate forty per cent of the nitrogen, thirty per cent of the phos- 

 phorus, and twenty per cent of the potassium contained in the 

 feeds used. 



3. The nitrogen in clover and alfalfa hay sold is to be regarded 

 neither loss nor gain to the soil. 



4. Losses in pasturing may be considered as follows: Nitrogen, 

 thirty per cent; phosphorus, fifty per cent, and potassium, 

 twenty per cent. (Good pasture may be considered the equivalent 

 to the production of one and one-quarter tons of mixed grass 

 hay per acre.) 



5. Loss in leaching may be considered at twelve to twenty 

 pounds of nitrogen per acre per year on cultivated fields of moder- 

 ately rich soil in humid regions, and about forty pounds per acre 

 on heavily manured fields or on soils of very high fertility , and under 

 heavy rainfall, especially during the middle of the growing period. 



7 A small amount of nitrogen is washed from the atmosphere as ammonia. 

 This amounts to about five pounds per acre per year. 



8 Shavings possess little or no fertilizing value. 



