No. 5. DEPARTMENT OP AGRICULTURE. 349 



as great as that from phosphorus alone in the corn crop and consider- 

 ably greater in the hay crops. 



When the liming has supplemented the use of fertilizers and 

 manure, it has maintained in the grain crops practically the same 

 additional increase over that produced by the fertilizers that it has 

 given on the unfertilized land, while in the clover and timothy the 

 liming has produced nearly twice the increase on the fertilized or 

 manured land that it has on the unfertilized land. This point has 

 been very conspicuous as the clover has been inspected in the field 

 each season. It has been plainly evident that lime alone is not suf- 

 ficient to maintain a full growth of clover on a soil so depleted of 

 other elements of fertility as the one under this experiment. 



Next to the hay crops, the corn has profited most from the liming, 

 as shown by the last line of the table, and this is what would be ex- 

 pected on the basis of the composition of the crops, for while a crop 

 of clover contains ten times as much lime as an equivalent crop of 

 wheat, it contains only about 4^ times as much as an equivalent crop 

 of corn. 



However, the lime content of the oats crop is twice as great as that 

 of v.'heat, and timothy contains about one-sixth the lime found in 

 clover, so that the composition of the crop does not fully explain its 

 requirement of lime. 



On the other hand, when we study the conditions necessary to the 

 maintenance of the worli of the micro-organisms of the soil by 

 which the soil nitrogen is converted into forms available to the crops 

 we cultivate, we can easily understand wliy clover should be first 

 and corn next in profiting by the use of lime. For unquestionably 

 the chief function of lime in the soil is not the direct feeding of the 

 crops we cultivate, btit the support of the nitrogen-gathering and 

 nitrifying bacteria, by combining with the nitric acid which it is 

 their province to produce and holding it in a form at once harmless 

 to its producers and suitable for absorption by the growing crop. 

 When the lime supply of the soil is deficient the nitric acid accumu- 

 lates until it becomes toxic to the organisms producing it, the soil 

 itself becomes acid, and tlie fixation of nitrogen ceases or is ma- 

 terially reduced. 



An acre of corn or of clover contains twice as much nitrogen as 

 an equivalent acre of wheat. Corn is able to secure this large quan- 

 tity of nitrogen because it grows during the summer months when 

 the nitrifying organisms of the soil are most active, and because the 

 cultivation of the corn assists these organisms in their work by ad- 

 mitting air to the soil, while clover gathers its nitrogen through the 

 aid of the bacteria inhabiting the nodules on its roots. To both 

 classes of organisms an acid soil is unfavorable, and the statistics 

 of crop production in Ohio show that the yield of corn is several 

 bushels per acre lower in the sections where such soils prevail than 

 in the regions "^^here the soil is underlaid with limestone. 



Wheat, however, is comparatively indifferent to soil acidity. The 

 largest wheat yields in Ohio are found over the sandstones and shales 

 of the northeastern counties, where the soil is generally acid, a fact 

 which is chiefly due to the larger use of fertilizers in these counties. 



The lime was first used in these experiments at the rate of a ton 

 of quicklime per acre, but during recent years finely ground raw 



