1% 



centimetre thick) remains richer in water, i. e. becomes saturated more 

 quickly and therefore lets more water flow into the deeper layers of the sub- 

 soil. The same result is shown by covering with ochre, such materials 

 as stable manure, straw, tan bark, and even with stones. Soil covered with 

 growing plants is even less per\'ious than the naked earth. 



Some practical workers recommend the use of peaty earth on sandy 

 soils. Thus Walz^ made use of the upper layers of a peaty deposit which 

 were 6 to 8 cm. deep and useless for fuel, in order to cover a field of poor 

 sandy soil 2 cm. deep, in February. Later this surface which had been 

 covered with peat and one adjoining it, but not so covered, were richly 

 fertihzed with stable manure. In the heat and drought of summer, 

 maize planted on the field mulched with peat showed a better growth and 

 furnished a higher percentage of yield. In the same way, later crops were 

 found to be more luxuriant on the plat of ground mulched with peat. 



The value of the peat, which Nerlinger- has demonstrated in exact har- 

 vest results, arises from its ability to soak up and retain the fertilizing 

 substances which otherwise, in sandy soil, would be washed away. I have 

 determined experimentally^ that fertilizing makes it possible for the plants to 

 give a better yield with less water, which explains the more favorable be- 

 havior in time of drought. 



Soils With a Plant Cover. 



It has already been said that soils with a cover of living plants allow 

 the least water to drain through. This is explained by the fact that plant 

 roots absorb the water. Comparative experiments'* prove that the water in 

 the soil is more quickly exhausted with a thick stand of plants, even if this 

 exhaustion does not increase proportionately to the density of the plant 

 growth. 



From these results, the difl^erence between a bare, broken soil and one 

 covered with a dense turf during hot, continued dry weather, can be ascer- 

 tained. Therefore, in nurseries on porous soil, it is by no means a matter 

 of indifl:'erence whether it is often hoed or whether turf and weeds are al- 

 lowed to form a dense covering. It is not a theoretical conclusion but an 

 often demonstrated fact that occasionally premature ripening and sterility 

 are produced in fruit trees, because the weeds and turf have taken up the 

 scanty supply of water. 



In forestry and trees in beds, if the seedlings do not make a dense 

 growth, their development is threatened. Gravelly soils without sufficient 

 humus content are also a menace for older plants from lo to 15 years of 

 age, especially if protection is not given on any side by larger plantations. 



1 Zeitschrift d. Landw. Yer. in Bavern 1S82; cit. in Biedermann's Centralbl. 

 1883, p. 136. 



2 Flihling-'s landw. Zeit. 1878, Part S. 



3 Sorauer, Nachtrag- zu den Studien liber Yerdunstung-. Forsch. auf d. Geb. d. 

 Agrikulturphysik, Yol. YI, Parts 1 and 2. 



4 Wollny, Der Einfluss der Pflanzendecke und Beschattung auf die physikalis- 

 chen Eig-enschaften und die Fruchtbarkeit des Bodens. Berlin, Parey, 1877, p. 128. 



