44 MINNESOTA STATE HORTICULTURAL SOCIETY. 



by impeding- the flow of the surface water allows it to soak into the 

 ground. The necessity of this in the case of clayey hillsides is 

 evident; on them, the surface of the soil, when exposed, will become 

 so hardened that the rain falling in summer showers penetrates the 

 land so very slightly that it is all evaporated after a very few hours 

 of sunshine, thereby, perhaps, rendering- the land harder and more 

 impermeable than before. 



(2.) The loss of water by its passing through the soil to the un- 

 derground water system may be considerable, but over this factor 

 we have very little control. The water-holding capacity of soils 

 varies very much, and successful cultivation depends largely on 

 their proper selection for different crops. This quality may often 

 be increased by the addition of organic inatter to the soil. In some 

 parts of Europe even the prunings of grape vines and willow twigs 

 are often used to mix with land to increase its humus; but the plow- 

 ing in of green crops and the use of stable manures are probably 

 the most practical means for improving the water-holding capacity 

 of the soil in this section. 



(3.) The loss of water by evaporation from the surface of the land 

 must be regarded the prime factor in the dissipation of the water in 

 the soil. This may be limited (a) by wind-breaks, (b) by mulching- 

 the surface of the soil and (c) by cultivation of the surface soil. 

 This latter method of prevention is not discussed here. 



Wind-breaks. It is necessary to allow of a circulation of air 

 among our crops in order to prevent serious losses from fungus 

 diseases. When the air is very much confined and circulates but 

 slowly, as in fields closely shut in by wind-breaks, there is liable to 

 be serious loss from rust, blight, mildew and the many diseases to 

 which plants are subject, but, nevertheless, we can secure sufficient 

 circulation of the atmosphere to get its beneficial action in preventing 

 diseases and yet avoid the greatly increased rate of evaporation due 

 to its very rapid circulation. How much the rate of evaporation is 

 increased by exposure to the winds was clearly shown bj' the ex- 

 periments of Prof. T. Russell, Jr., of the Signal Service, in 1887. The 

 results of these experiments show that with the temperature of the 

 air at eighty-four degrees and a relative humidity of fifty per 

 cent, evaporation with the wind blowing at five iniles an hour was 

 2.2 times greater than in a calm; at ten miles, 3.8; at fifteen miles, 4.9; 

 at twenty miles, 5.7; at twenty-five miles, 6.1; and at thirty miles per 

 hour the wind would evaporate G.3 times as much water as a calm 

 atmosphere of the same temperature and humidity. Now, if it is 

 considered that the winds which sweep our prairies average a 

 velocity of ten or more miles per hour, and not unfrequently thirty 

 miles an hour, the losses which may be prevented by the judicious 

 use of wind-breaks can to some extent be appreciated. Then, too, it 

 is probable that the terribly drying effect of some of the winds 

 which occasionally sweeji over the prairies is not considered in the 

 above figures, nor is the loss which conies from increased transpira- 

 tion from the foliage, and whichisno inconsiderable item. It will be 

 understood from these facts that the wind is an important factor in 

 the dissipation of the water in the soil, and that its injurious action 

 may be prevented to a considerable extent by the judicious use of 

 wind-breaks. 



