20 MASS. EXPERIMENT STATION BULLETIN 195. 



believe, to restore the "sick" soils it will be necessary to rotate on a three 

 or four j^ear basis, is an open question, but one which should be seriously 

 considered by those whose land is in very poor condition. It is to be 

 hoped, however, that some treatment will be discovered which will render 

 this unnecessary. 



Continued examination of normal and "sick" soils during 1917 and 

 1918 has served to substantiate the findings of the first year. Almost 

 invariably there has been found to be a relationship between the organic 

 matter content of a given soil and the development of the crop. This 

 was especially true in the case of old fields which had been heavily limed, 

 and fertilized for years with "chemical" fertilizers. These same fields, 

 as a rule, had had no addition of organic matter, except such as came from 

 the cottonseed apphed, or from the stalks plowed under. 



Our light and heavy soils, of course, vary widely in the content of 

 organic matter when in a virgin condition, and, as a rule, the light types 

 are the first to be depleted of their organic matter. These also are the 

 soils which contain normally the smallest amounts of organic matter. 

 Continued liming depletes the organic matter very quickly, and in this 

 practice we have undoubtedly exceeded the limits to which we may go and 

 maintain a favorable amount of humus in the soil. 



Some of the soils show a very low humus content, — even less than 

 half of 1 per cent, — and in some cases, even on the heavier types of soils, 

 we found less than 2 per cent. The natural organic matter or humus 

 content of our tobacco soils varies from about 1| to 5 per cent or more, 

 depending on the type of soil. It can be plainly seen that there is certainly 

 a deficiency in many cases, and this should be remedied as soon as possible. 

 Very few of the soils examined contained what would be considered the 

 normal amount of humus for their type. 



Organic matter is a very important factor in any soil, and particularly 

 tobacco soils which are, in this section, cropped for years without any rest 

 or rotation. Sufficient attention has not been paid to keeping up the 

 supply of organic matter in the soils. 



Organic matter affects the soil in many ways, both physically and 

 chemically, and might almost be called a "soil regulator." Physically, 

 it lightens heavier soils and binds lighter soils together and tends to make 

 them loamy. It also increases the moisture-holding capacity enormously, 

 and thus acts in a beneficial manner. Chemically, it adds to the plant 

 food of the soil, as it contains the elements required by plants for food. 

 Haskins' experiments at this station, in which he applied varying amounts 

 of peat to some "sick" fields, showed very plainly that the peat exercised 

 a beneficial effect on the growth of tobacco. These effects were due, 

 probably, not only to the increase of organic matter in the soil, and the 

 consequent action on the mechanical condition and water-holding capacity, 

 etc., but also to the increase in soil acidity resulting from its application. 



In our own experiments on "sick" soils — light and heavy — in the past 

 two years we have shown conclusivelj'- that an application of even moderate 



