2^6 



V. Seelhorst' treats the same subject and comes to the conclusion that 

 so far as moisture is concerned, rye exhausts the field much less than wheat. 

 This circumstance is very important when planting possible subsequent crops 

 for green manuring, for, after wheat, which is cleared later from the field, 

 tills crop not only reaches the soil later, but also finds the soil much drier. 

 Clover exhausts the water in the soil very greatly so that, aside from the fact 

 that the soil easily becomes loosened by the clover stubble, in dry years, the 

 winter crops following the clover can only develop slowly and unevenly be- 

 cause of the lack of moisture. 



On the other hand, the potato, at least the variety ripening moderately 

 early, seems to form a very good early crop, since it leaves the soil fairly 

 moist. Peas also form a good early crop for winter grain. Oats are con- 

 sidered by V. Seelhorst to be especially unfavorable, not so much 

 because they exhaust the nutritive substances as because they remove water 

 to so marked an extent. 



In connection with field plants, we should consider also the injurious 

 influence of grass. It is easy to understand that a close turf keeps water 

 from the roots of plants, especially fruit trees and impoverishes the friable 

 soil, but recently a direct poisonous effect of grass- has been mentioned 

 which may possibly be due to the fact that beneficial bacteria species are 

 suppressed by it and injurious ones favored. In the case given, 

 the roots of the apple trees were long, abnormally thin and browned, the 

 leaves were very light in color and dropped 4 days earlier. The foliage was 

 sparse, the wood growth scanty. As soon as the roots or even only a greater 

 part of them reached soil not covered by grass the phenomena of disease dis- 

 appeared. These phenomena agree essentially with those produced on heavy, 

 impervious soils, with a scarcity of oxygen, so that it seems in no way neces- 

 sary to assume any poisonous action. We find, in many cases, especially on 

 light soils, that the turf does no injury, if care is taken, to have nutritive sub- 

 stances within reach of the roots. On close clay soils, the grass is kept green 

 for a long time by the water rising by capillary action from the subsoil, 

 thereby removing a great deal of moisture from the subsoil without return- 

 ing it in quantities worth mentioning during the period of vegetation, since 

 the grass uses the atmospheric precipitation itself. 



Wilting. 



In discussing "physiological wilting," mention was made of the fact 

 that the phenomena of wilting can appear even with an abundance of mois- 

 ture in the soil, since the roots function incompletely. In soils with a high 

 content of soluble salts, the water, under certain circumstances, can be held 

 so fast that the roots meet their need only with great difficulty. Phenomena 



1 V. Seelhorst, Untersuchungen liber die Feuchteigkeitsverhaltnisse eines Lehm- 

 bodens unter verschiedenen Friichten. Journ. f. Landwirtsch. 1902. Vol. 50. cit. Cen- 

 tralbl. f. Agr. Chemie 1903. Part 6. 



~ Bedford, Duke of, and Pickering, Spencer U., The effect of grass on trees. 

 Third report of the Woburn exper. fruit farm. London, 1903. 



