EXPEEIMENTAL WORK WITH RAW ROCK PHOSPHATE. 75 



with the yields from the plots receiving mixtures of acid phosphate 

 and cottonseed meal, and in every case the phosphate-cottonseed-meal 

 mixtures gave substantially greater yields than the cottonseed meal 

 alone. 



The yields obtained in the cotton experiment, however, were more 

 favorable to acid phosphate than to the raw rock, but the plots 

 treated with the latter phosphate mixed with cottonseed meal gave a 

 greater yield than those treated with cottonseed meal alone. 



It may be said that while these experiments _give a very limited 

 amount of data on the fertilizer value of raw rock phosphate they 

 indicate that even light applications of this material when supple- 

 mented with cottonseed meal may produce substantial increases in 

 the yield of corn and cotton. 



Of the nine field experiments with raw rock phosphate conducted 

 by the Mississippi station only two were continued beyond four 

 years. In these two the applications of the ground raw rock were so 

 light that results can hardly be considered indicative of the value of 

 this material. In practically all of the experiments, however, plots 

 receiving raw rock phosphate, either alone or in combination with 

 other fertilizer materials, have shown substantial increases over the 

 check plots with which they were directly comparable. 



MISSOURL 



The Missouri station advised the use of raw rock phosphate in 

 1905 ^ and 1910,^ but it was not until 1914 that any data obtained 

 from field work was published by this station. 



In an experiment described by Miller, Hutchison, Douglass, and 

 Hudelson,^ a study was made of the effect of various fertilizer treat- 

 ments on both drained and undrained land in a four-year rotation 

 of corn, oats, wheat, and cowpeas (with cowpeas grown and turned 

 as a catch crop between the regular crops of the rotation). 



The field selected for- this experiment was a 10-acre tract of very 

 level poorly drained prairie land lying one-half mile west of Van- 

 dalia. The soil was a clark-gray silt loam 7 to 9 inches in depth un- 

 derlain by a silty clay. The field was divided into two equal parts 

 and one half tiled and the other half left untiled. Each half was 

 then divided into seven plots of seven-tenths acre each, running cross- 

 wise of the drained and undrained areas. The corresponding plots 

 in each area were then treated as follows: Manure at the rate of 8 

 tons per acre, and raw rock phosphate at the rate of 600 pounds per 

 acre every four years before corn, bone meal 150 pounds per acre, 

 and potassium chloride 50 pounds per acre, twice during a rotation. 



iMo. Agr. Bxpt. Sta., Circular of Information No. 22, p. 25 (1905). 

 «Mo. Agr. Bxpt. Sta., Bui. No. 84, p. 33 (1910) : BuJ. No. 86, p. 91 (1910). 

 »Mo. Agr. Expt. Sta., Bui. No. 118, 443-475 (1914). 



