EXPERIMENTAL WORK WITH RAW ROCK PHOSPHATE. 57 



since its yield nearly equaled that of the raw-rock plot. In 1892 and 

 1894 (particularly in the latter year), however, the plot receiving 

 raw rock phosphate two and four years previously forged ahead very 

 noticeably. 



In 1896 Merrill ^ published the results of the box experiments be- 

 gun by Ballentine ^ a number of years before and continued after 

 the latter's death. The work was carried on still further, however, 

 and all the results published by Merrill ^ in 1899. 



This experiment was undertaken in order to determine the rela- 

 tive availability of various phosphates and also to test the ability 

 of some of the common crops to obtain phosphoric acid from these 

 different sources. The work was conducted in one of the green- 

 houses, and the plants grown in wooden boxes 14 inches square and 

 12 inches deep. The boxes were filled to within 1-| inches of the 

 top with 120 pounds of sand. The sand was taken from a knoll 

 near the river, at a depth of 3 or 4 feet, and was nearly free from 

 organic matter. Traces of phosphoric acid were present. Before 

 filling the boxes, the sand was carefully screened and mixed 

 thoroughly with the various fertilizers. 



Eighteen species of plants were grown, representing seven orders: 

 (1) peas, horse beans, clover, and alfalfa (Leguminosse) ; (2) tur- 

 nips, rutabagas, cauliflower, and kohlrabi (Cruciferae) ; (^) barley, 

 oats, and timothy (Graminese) ; (4) tomatoes and potatoes (Solan- 

 acese) ; (5) carrots and parsnips (Umbelli ferae) ; (6) buckwheat 

 (Polygonaceae) ; and (7) sunflower (Compositse). 



It was planned to carry each plant through three periods of 

 growth, but the clover would not ftiature in the time it took for the 

 other plants to do so, hence only two crops were grown. The sun- 

 flower and buckwheat did not thrive under the conditions of the 

 experiment; and, after a single trial, were replaced by carrots and 

 parsnips, which were grown for the two following periods. 



In each period 12 boxes were employed for each kind of plant. 

 The boxes were divided into three sets of four each, the various 

 phosphate treatments as well as the checks being run in triplicate. 



No attempt was made at pollination, and since but few insects 

 were present during the growth of the plants, the fruiting was very 

 irregular. As soon as the plants seemed to have attained their 

 maximum development they were harvested, dried, weighed, and the 

 total amount of dried matter determined for each crop grown. 



The phosphates used in this experiment were acid phosphate, 

 Redonda phosphate (phosphate of iron and alumina) made largely 

 citrate soluble by ignition, and Florida finely ground phosphate rock 



iMe. Agr. Exp. Sta. Ann. Kept, for 1895, p. 10-14 (1896). 

 2 Me. Agr. Exp. Sta. Ann. Kept, for 189.3 (1894). 

 *Me. Agr. Exp. Sta. Ann. Kept, for 1898 (1899). 



