CANADIAN FIELD EXPERIMENTS 509 



plot 13 yielding only 1.2 bushels more wheat, 2.3 bushels more 

 oats, and .4 bushel less barley than plot 4. The 300 pounds of cal- 

 cium sulfate on plot 20 produced .4 bushel more wheat, the same 

 yield of oats, and .9 bushel less barley than the 500 pounds of acid 

 phosphate on plot 21. By referring to Table 78, we find that as an 

 average of six 4-year periods, 640 pounds of calcium sulfate pro- 

 duced practically no effect (12^ cents per acre in four years), while 

 dissolved bone black carrying 42 pounds of phosphorus produced 

 an average increase of $12.17. These results certainly indicate that 

 phosphorus is not the limiting factor in crop yields on the Ottawa 

 soil. 



The effect produced on oats by the fine-ground bone is probably 

 due to the nitrogen contained in the bone. It is a common ob- 

 servation that oats respond to nitrogen more rapidly than most 

 other crops on the same soil, and it will be observed that sodium 

 nitrate alone (plot 15) produced practically the same effect on 

 oats as the nitrate and acid phosphate combined. Where nitrogen 

 was provided, the raw phosphate (plots 5 and 7) produced a larger 

 average increase on oats than did the acid phosphate (plots 10 

 and u), during the first nine years. 



A study of the results with wheat and barley indicate that potas- 

 sium is the first limiting element for those crops. As an average of 

 the first ten years, the largest yield of wheat was produced by po- 

 tassium chlorid, aside from the farm-manure plots; and the second 

 largest yield was with ashes (plot 14; compare with 13). Sodium 

 chlorid also produced some increase in the yield of wheat, and with 

 barley the 300 pounds of sodium chlorid produced the largest yield, 

 aside from the two heavily manured plots. Even acid phosphate, 

 containing much calcium sulfate and an acid salt of phosphorus, 

 may liberate some potassium. It may be questioned whether potas- 

 sium or nitrogen is most limiting for the barley crop, but it is plain 

 that phosphorus is not the limiting element. Even during the sec- 

 ond ten years, the 150 pounds of potassium chlorid or the 300 

 pounds of sodium chlorid rank higher than 500 pounds of bone 

 or 500 pounds of acid phosphate, in either trial (plots 9 and 21), 

 and also far above the slag phosphate (plot 4) . 



On plot 6 the raw phosphate was applied in connection with 

 " actively fermenting " manure, and it may have produced some 



