17 



FERTILIZERS FOR ALFALFA. 



One ton of alfalfa bay contains ajiproxiniately 44 lbs. 

 of nitrogen, 10.2 lbs. of pbospboric acid, and 33.6 lbs. 

 of potasli. Hence a crop of four tons contains as mucb 

 nitrogen as is found in 2,450 lbs. of cotton seed meal, as 

 mucb pbospboric acid as is contained in 330 lbs. of bigb 

 grade acid pbospbate, and as mucb potasb as is contain- 

 ed in 1,075 lbs. of kainit. It would cost, to buy all these 

 amounts of plant food in tbe form of commercial ferti- 

 lizers, approximately |35.00. Fortunately not all of this 

 is removed from the soil, the greater part being the value 

 of the nitrogen, the largest proportion of which the al- 

 falfa doubtless gets from the air. It would, however, re- 

 quire about |8.75 worth of phosphate and kainit to re- 

 place the amount of phosphoric acid and potash which 

 would be removed from the soil of an acre by a crop of 

 four tons. Hence it is evident that even the richest 

 prairie soils, if cropped for many years in alfalfa, will 

 need to have their supplies of phosphoric acid and pot- 

 ash replenished by the application of manure or ferti- 

 lizers. This will be especialh' true if Johnson grass hay 

 has previously been removed from these soils for a num- 

 ber of years, thus making heavy drafts on the soil's sup- 

 ply of these two minerals. 



According to Wolff, one ton of alfalfa hay contains 70 

 pounds of lime, or 280 pounds in a crop of four tons. In 

 three experiments on the station farm at Auburn lime 

 has proved highly beneficial to the gTowth, permanency 

 and hardiness of alfalfa. 



In the case of soils not rich in lime it will be necessary 

 from the beginning to apply this material, as is clearly 

 shown in the experiments on the station fanii at Auburn. 

 Not only do lime and phosphoric acid directly stimu- 

 late the growth of alfalfa on soils deficient in these min- 



