368 STATE BOARD OF AGRICULTURE. 



as suitable quality of crops. If it is necessary to apply this material to 

 the mineral soils to increase the available supply the amount required 

 should be considered in estimating the returns from the land. 



Chemical analyses and field experiments have shown that most Michi- 

 gan soils are deficient in and respond to applications of phosphoric 

 acid. The cost of such applications therefore may reasonably be in- 

 cluded in calculating the returns. This may be simplified by charging 

 the cost of a 400-pound application of 16% acid phosphate per acre 

 every four years. This amount is suflQcient to produce approximately 

 25 bushels of wheat, 40 bushels of corn, 50 bushels of oats and 2 tons 

 of clover not including the straw and stover. The majority of our soils 

 also need approximately two tons of ground limestone every six years 

 and the cost of this should be spread over the various crops as shown 

 later. 



Nitrogen is present in such quantities that the supply must be main- 

 tained and in many soils increased in order to give the most economical 

 yields. The farmer is warranted therefore in adding the cost of replac- 

 ing this nitrogen by means of legumes to the price of his products. If 

 conditions are such however that nitrogen must be applied in the com- 

 mercial form the cost of adding this to the soil should be included. 



This raises the question of the cost of production of a pound of nitro- 

 gen on the farm. The cost of production of a pound of nitrogen by 

 means of leguminous crops in a rotation is difllcult to determine. It 

 should be conceded that much of the benefits derived from the use of 

 lime is due to its effect on the legumes such as clovers and alfalfa. It 

 seems fair to charge two-thirds the cost of the lime to these crops and 

 also the phosphate that should be added to the soil for their benefit. 

 If two tons of lime are applied per acre and endure six years and a four- 

 year rotation is followed and two seediugs of clover, vetch or soy beans 

 are obtained and one hundred pounds of acid phosphate are added to 

 each seeding the cost of nitrogen runs from five to eight cents a pound. 

 If no lime is added to the land naturally the cost is less or from two to 

 four cents. Alfalfa is the cheapest source of nitrogen. On the same 

 basis as in the first case above, nitrogen may be produced for less than 

 one-half w^hat it costs when obtained by means of other legumes. If the 

 crop stands four years instead of six the cost is slightly higher. 



