Part II.] :MAINTENANCE OF SOIL FERTILITY. 35 



Twenty-three years ago the Ohio Experiment Station began 

 an experiment in the use of fertilizing materials on crops grown 

 in a five-year rotation of corn, oats, wheat, clover and timothy, 

 on land that had been used for the general production of such 

 crops since its reclamation from the forest seventy years 

 earlier. The next year a duplicate of this experiment was 

 begun on a different soil that had been pastured chiefly by 

 dairy cattle for twenty-five years previously. In 1904 two 

 experiments in the culture of corn, wheat and clover in three- 

 year rotations were begun, the one on a grain farm in south- 

 western Ohio, the other on a live-stock farm in the hill country 

 of southeastern Ohio, these farms being from 40 to 150 miles 

 apart. The outcome of these tests has been that 100 pounds 

 of 14 per cent acid phosphate, when used alone, has produced 

 an average increase to the value per acre of between $4.09 and 

 $4.85 per acre in each of the four tests, whereas potassium, 

 when used alone or with nitrogen only, has never returned its 

 cost. When potassium has been used with phosphorus, how- 

 ever, there has been a larger gain on the grain farms, both 

 total and net, than that from phosphorus alone, although the 

 potassium remained unprofitable on the dairy farm. 



The station has also conducted an experiment in which 

 potatoes, wheat and clover have been grown for twenty-three 

 years in a three-year rotation on land, half of which was cleared 

 from the forest for the purpose of this test, and one in which 

 tobacco, wheat and clover have been grown in rotation for 

 eighteen years, these tests being located in different quarters of 

 the State. In both tests wheat has shown a decided preference 

 for phosphorus over potassium. During the earlier years the 

 potatoes showed a similar preference, but of late phosphorus 

 seems to have largely lost its effect on this crop, while the gain 

 from potassium is steadily increasing. The tobacco crop has not 

 been grown over so long a period as the potatoes, but its prefer- 

 ence seems to be for potassium rather than for phosphorus. 



The outcome of these experiments is in harmony with those 

 of the Massachusetts Experiment Station, in which truck or 

 similar crops have been largely grown, — crops grown chiefly 

 for their roots or stems and leafy parts rather than for their 

 seeds, and which have shown a larger response to potassium 



