160 



clover; Imt the unlimed clover shows in every case a lower yield from the other 

 carriers than from sodium nitrate. 



Attention is es])ecially called to the fact that the yield of the unlimed clover, 

 followint: the complete fertilizer containing annnonium sulphate as the carrier 

 of nitrogen (plat --t). is practically identical with that of plat 8, fertilized with 

 potassium chlorid alone; whereas the limed half of this plat produces a yield 

 equaling the average yield from fertilizers in which the nitrogen is carried in 

 sodium nitrate. 



Taking the experiment as a whole, it is evident that phosi)horus has been the 

 controlling element in producing increase in the cereal crops, and that, after 

 phosphorus, nitrogen ranks next in importance. With clover, however, lime is 

 evidently the substance first in demand. After lime is supplied, then phosphorus 

 and i)otassium are required, and in the order named. Given plenty of lime, it 

 would seem that nitrogen might be almost entirely dispensed with as far as the 

 clover is concerned, for the results of the test indicate that the increase of 

 clover, following sodium nitrate, is due rather to the sodium than to the nitro- 

 gen, the sodium apparently serving to some extent as a base with which the 

 excess of soil acids may combine. This work is still in the tentative stage, but 

 its results show a much greater lime reiiuirement in the soils which have 

 leeeived no sodium nitrate than in those which have been dressed with that 

 substance. 



The effect of this liming on the cereal ci-ops has been to increase the yield of 

 corn and oats by about 1(» bushels per acre, and of wheat by a smaller quantity. 

 The liming has also apparently slightly increased the effectiveness of the ferti- 

 lizers, Itut this increase has been small as compared with that observed on the 

 clover crops. 



The outcome of these experiments raises a host of questions ; 



In the first place, what is the meaning of the increasing acidity of this hard- 

 run soil? Is it due to an organic or a mineral acid? If to the former, why does 

 its increase seem to be in inverse ratio to the amount of organic matter left 

 in the .soil by the growth of crops, and why does the use of sulphuric acid in 

 fertilizers increase th(> difficulty? If the acidity is of inorganic origin, what is 

 the cause of its increase on soils which have not received acidulated fertilizers? 

 Is it the acid itself which is injurious to clover, or is the acidity merely a 

 symptom of some other toxic condition? And why does the common red clover 

 suffer so much more from this toxic condition than the cereal crops, and alfalfa 

 still more than red clover? In what way does lime act to correct this unfavor- 

 able condition? Does it simply serve as a fertilizer, satisfying the lime hunger 

 of the plant ; and is its superior effect on clover, as compared with th cereals, 

 due to the much greater relative lime requirement of clover than of the cereals? 

 Or is the effect chiefly due to the setting up of conditions more favorable to 

 nitrification and to the functions of the symbiotic bacteria? What is the mean- 

 ing of the great effect of sodium nitrate on clover on unlimed land, and of its 

 meager effect on clover on limed land? Is the sodium furnishing an alkaline 

 liase to neutralize the acidity of the soil? If this were all that is required, 

 would not a large application of sodium nitrate dispense with the necessity for 

 lime, which it seems not to have done, in the case of these experiments, although 

 it has consideral)ly reduced the effect of lime? 



THE STUDY OF SOIL ACIDITY AT WOKfRN. 



The Wol)urn exiieriments of the Royal Agricultural Society of England are 

 conducted upon " a light sandy loam, deficient in lime," a description (luite 

 applicable to the Wooster soil of the Ohio station. In these experiments 

 wheat and barley have been grown in continuous culture since 1870, with dif- 

 ferent fi'rtilizing compounds. IMat No. 2 has received a mixture of the sul- 

 phate and chlorid of ammonia without any other fertilizing material, and for 

 twenty years this plat produced good crops of barley; but at the close of this 

 period ;i condition set in nmch resembling that which has become manifest in 

 the clover in the Ohio experiments, the growth first being sjjotted and uneven, 

 and finally failing almost completely. This soil was found to show a decided 

 acid reaction to the litn.ms test. In ISiH lime was ai)plied to one-half of this 

 l)lat. with the result that the former luxuriant growth of barley was restored, 

 whereas on the milimed half the growth became continually more feeble. The 

 wheat <'rop did nut begin to fail on the similarly treated ])lat until several years 

 later, but by 10(J3 it also was showing signs of distress. In pot-culture tests 



