EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 69 



A summary and discussion of this experiment after 18 years' work 

 was published by Brooks^ in 1915. 



The field selected for this experiment was fairly level, but while 

 the soil as a whole was a medium silt loam, the plots varied somewhat 

 in physical character. Moreover, the fertility of the various plots ( as 

 determined by a crop of corn grown the year previous to the appli- 

 cation of fertilizer) was apparently not uniform. The field had been 

 in grass for a number of years preceding the experiment, and had 

 received annually moderate top dressings of chemical fertilizers. In 



1896, the field was plowed, divided into 13 plots of ^ acre each, and 

 planted to corn without the addition of any fertilizer whatever, in 

 order to determine the relative natural fertility of the various plots. 

 The corn was cut green and weighed. Apparently there has been 

 some confusion in the statement of the yields of corn obtained in this 

 preliminary test, for in Public Document No. 33,^ published shortly 

 after the experiment was begun the yields obtained on plots 1 to 13, 

 inclusive, are in the reverse order from those given in Brooks's sum- 

 mary of this experiment published in Bulletin No. 162. On account 

 of this confusion the yields obtained in this preliminary test can not 

 very well be taken into consideration in figuring the relative efficiency 

 of the phosphate treatments. 



The various phosphates to be tested were applied in the spring of 



1897, together with liberal amounts of potash and nitrogen. In 



1898, and again in 1914, all plots were treated with hydrated lime at 

 the rate of 1 ton per acre, which was spread upon the plowed land 

 and harrowed in. The annual application of fertilizer materials 

 varied somewhat, the most important change being an increase of 

 50 per cent in the nitrate nitrogen and the actual potash in 1901. 

 Since that date the annual rate of application per acre has been 

 91.2 pounds of nitrogen, 152 pounds of potash, and 96 pounds of 

 phosphoric acid. 



In order that the less soluble phosphates might have their full 

 effect " a stock of organic matter was maintained in the soil by turn- 

 ing under heavy crops as follows : Winter rye in 1901, buckwheat in 

 1912, and rye in 1913, and by introducing grasses and clovers, 1905 to 

 1907, and turning under a heavy growth of grass in 1908." 



Hopkins^ considers that the supply of organic matter thus fur- 

 nished was inadequate to meet the requirements of the crops and 

 receive full benefit from the raw rock phosphate treatments. 



The following table taken from Bulletin No. 153, of the Massa- 

 chusetts station gives the increases in yield of various crops (over 



»Mass. Agr. Expt. Sta., Bui. No. 162 (1915) 



*Mass. Agr. Expt. Sta., 10th Ann. Kept., p. 17 (1898). 



«I11. Agr. Expt. Sta., Circ. No. 186, p. 13 (1916). 



