No. 7. DEPARTMENT OF AGRICULTURE. 447 



lor the use of succeeding crops of grain or grass. Tliis practice may 

 be continued until the clover system fails, clover itself, used as 

 a soil stimulaut, beiug the first crop to fail. Clover failure may re- 

 sult from several ditferent causes. If grown too frequenli/ on 

 the land, it is quite probable that clover sickness may develop, al- 

 though it still remains to be proven whether clover sickness is a fact. 

 On some lauds clover may fail because of the development of soil 

 acidity; but the most common cause of clover failure that I have 

 noted on land that has grown clover well in former years is the 

 lack of sufticient mineral plant food in available form. 



After the failure of the clover system of grain farming, we may 

 make use of still more powerful soil stimulants, as laud-plaster, or 

 heavy applications of caustic lime, not applied merely in sufticient 

 amount for what we might call the legitimate purpose of correcting 

 soil acidity, but rather for the purpose of forcing the soil to give 

 up larger amounts of plant food than it would otherwise furnish. 



After this system fails, we next turn to the ordinary complete 

 commercial fertilizer system, in which we apply not sufficient plant 

 food to meet the needs of the crops grown, but only enough to sup- 

 plement that which can still be forced from the soil. Of course 

 the effect of this system is to make the laud poorer and poorer until 

 the soil furnishes so little and so much fertilizer is required for the 

 moderate or meager crops produced that the business becomes un- 

 profitable and not infrequently the land is then abandoned for agri- 

 cuiturjjl purposes. 



Shall we call this soil exhausted? No, it is not exhausted. No 

 soils ever become exhausted, not absolutely devoid of plant food, 

 and no soils ever become so completely ruined that they cannot be 

 restored by some system of improvement. Just what system should 

 be adopted will depend largely upon the character of the soil. If 

 nitrogen is the only element whose total supply is so greatly depleted 

 as to render the land unprofitable for cropping, and if the organic 

 matter in which the nitrogen was stored has become so reduced that 

 the mineral matter is not made available in sufficient amounts for 

 proiitable crops even though the total supply in the soil may be 

 large, then the productive capacity of the land can be restored by 

 storing the soil with decaying organic matter rich in nitrogen. This 

 is most likely to be the condition on sloping hill land whose subsoil is 

 rich in mineral plant food and whose surface soil is washed away at 

 least as rapidly as the plant food is removed by the crops. 



If, however, the total supjjly of phosphorus has become so de- 

 ficient that snlficient amounts cannot be liberated to meet the needs 

 of maximum proiitable crops, which is likely to be the case with 

 many upland soils of level, or nearly level, topography, then that ele- 

 ment should be restored in liberal amounts in order to bring back 

 the i)ower of the soil to grow clover as vrell as other crops. If both 

 phosphorus and nitrogen are deficient, then phospliorus and nitro- 

 gen should be returned. And if potassium is so lacking in the soil 

 that liberal supplies of decaying organic matter cannot liberate suf- 

 ficient potassium for large crops, a condition sometimes though 

 rarely found, then certainly potassium should be supplied. 



You may ask: How is one to know^ about the total supply of nitro- 

 gen and of phosphorus and of potassium contained in tlie various 

 soils of the State? What soils are acid, and how acid; and what are 



