860 EXPERIMENT STATION RECORD. 



THE INFLUENCE OF METEOROLOGICAL ELEMENTS. 



This can not be disregarded if we wisli to obtain a clear insight into 

 the cause of the widely varying condition of moisture of soils under 

 natural conditions, because the physical properties of the soil itself are 

 influenced by the average course of the elements (climate) and their 

 behavior at different times (weather). 



The effects of climate may be thus generally stated : A higher degree 

 of moisture in the soil accompanies coi)ious precipitation, greater 

 humidity of the atmosphere, moderate movement of the air, lower tem- 

 perature and greater water capacity of the soil, while a drier condition 

 of the soil is caused by the reverse circumstances. For a particular 

 case the effects can only be understood by knowing the course of the 

 individual elements and the constitution of the soil. 



The relation of the weather to the humidity of the soil is many 

 sided. 



Although the quantity of precipitation in the countries of middle 

 Europe is smaller during the cold season than during the warmer parts 

 of the year, the wetting of the soil is very much more complete in the 

 former than in the latter case on account of the diminished evaporation 

 due to a lower temperature. This is particularly true of soils covered 

 with plants, because the latter, as a rule, use up the water obtained by 

 the soil from the atmosphere during the period of growth, and some- 

 times a part of the water stored up during the cold season also.' From 

 these facts it follows that the water collected in the soil during the 

 period of no growth (winter moisture) may, under certain circum- 

 stances, be very important for vegetation.^ 



In the dry season the influence of evaporation is as a rule predomi- 

 nant. In long periods of dryness evaporation may cause an equalizing 

 of humidity in soils of diflerent physical constitution, independently 

 of how high the moisture was originally.^ The differences in humidity 

 between covered and bare soils show themselves more strongly, how- 

 ever, under such circumstances. This is also true for uneven, dark- 

 colored soils, compared with smooth light-colored soils,* 



Winds influence evaporation to a remarkable degree, and therefore 

 exert a great influence on the humidity of the soil. The evaporation 

 varies with the velocity of the wind. In the case of westerly and north, 

 erly winds, which are moist as a rule, the evaporation is less than 



IE. Wollny, Der Einfluss der Pflanzenclecke imd der Beschattung auf die physi- 

 kalischen Eigenschaften nnd die Fruclitbarkeit des Bodens, Berlin, 1877, p. 119; 

 Forsch, Geb. agr. Pbys., 4, p. 85. F. von Hciliuel, Mitt, aus dem forst. Versuch. 

 Oesterr., 1879; Forsch. Geb. agr. Phys., 4, p. 435. 



^G. Havenstein, Landw. Jabrb., 7. 



3C. Eser, Forsch. Geb. agr. Pbys., 7, p. 1. 



<E. Wolbiy, Der Einfluss der Pflanzendecke nnd der Beschattnng auf die physi- 

 kaliacbeu Eigenschaften und dieFruchtbarkeit des Bodens; Forsch. Geb. agr. Phys., 

 3, p. 147; 12, p. 386. 



