478 IOWA ACADEMY OF SCIENCE Vol. XXV, 1918 



turned under. It has been found that Japanese millet is nor 

 able to utilize so-called inert phosphorus from raw rock. Ac- 

 cording-Iy Japanese millet was immediately seeded on these green 

 manured soils. The millet was allowed to mature and then was 

 harvested. The yield was calculated and the amount of phos- 

 phorus contained in the crop was compared with the yield of mil- 

 let. Analyses were made also to determine tlie amount of phos- 

 phorus in the soil at ditferent stages of growth, soluble in fifth 

 normal nitric aoid. In connection with this problem approxi- 

 mately 550 determinations of so-called available and total phos- 

 phorus were made. 



It was found that the greatest yield of millet was produced 

 from the soils on which alfalfa, bearded barley, durum wheat, 

 and cow-peas had been turned under as green manures. These 

 higher yields accompanied a lower percentage of residual phos- 

 phorus in the soil and a consequent lower availability of this re- 

 sidual supply. Where any one of the four above mentioned crops 

 was used as a green manure and thus available phosphorus was 

 formed a profitable increase in total yield of millet was obtained 

 over the check. 



There are numerous common cereal crops besides millet which 

 make a much better growth if the phosphorus in the soil is in an 

 available form. 



From the results of this experiment it seems possible that the 

 practice of manufacturing soluble or available phosphorus in the 

 soil by aid of certain green manure crops may prove a valuable 

 asset to an increased crop production in the United States. 



Agricultural Experiment Station, 

 Iowa State College. 



