LECTUKES AND ESSAYS READ AT INSTITUTES. 223 



and cultivation. So far as we control it, the fertility depends upon the pro- 

 portion existing between the crops we remove and the fertilizers we apply. 



DRAINAGE. 



An undrained soil is subject to two unfavorable conditions. First, all the 

 water that falls aftercomplete saturation of the soil must needs run off over 

 the surface, and, instead of imparting fertility, dissolves it out and carries it 

 off. Second, evaporation only can reduce the saturated soil to a proper con- 

 dition of moisture, and the constant evaporation of a large quantity of water 

 from the surface soil destroys its heat, keeping the temperature too low for plant 

 growth for an undue length of time. It is a well known fact in science that 

 any liquid, water especially, in passing to a gaseous form uses up or renders 

 latent a large amount of heat. Translate this, and in the language of prac- 

 tice it would read "A wet soil is always a cold one," An incidental effect of 

 evaporation, too, is the formation of a crust at the surface, and the soil in 

 drying bakes and cracks. 



Some idea of this cooling effect of evaporation may be had from the follow- 

 ing calculation. I do not pretend to accuracy, as I have not all necessary 

 data, but it is in the main correct and errs, if at all, on the side of small 

 figures and the less startling results. It is a well known fact that water, 

 after heating to 212°, requires 966° additional heat to convert it into steam 

 or vapor whose temperature is also 212°. Arithmetic, by the aid of tables of 

 specific heats and gravities, furnishes the following: Two pounds (about a 

 quart) of water, converted to vapor by evaporation, destroys heat enough to 

 lower the temperature of 1,932 pounds (almost a ton), of water one degree. 

 This would lower four tons of common earth through one degree. Further, 

 the evaporation of seven barrels of water from an acre of ground will destroy 

 heat enough to lower the temperature of the whole acre one degree, and to the 

 depth of one foot. But as much as 50 barrels are sometimes evaporated in a 

 single day. We may call this scientific nonsense, essay farming, or what we 

 please, but there is not one of us but suffers under its truthfulness. A proper 

 draining of the soil, either natural or artificial, must not be overlooked in 

 preparation for cereals. They are very sensitive to wet and cold, and if noth- 

 ing better, open ditches or furrows should provide means for surplus water to 

 escape. By under-draining it sinks into the soil, giving up the ammonia it has 

 brought down, and filters into the drains nearly pure water. This is not an 

 essay on under-draining, but we all know that when water escapes from below 

 rather than from the surface, the soil is left porus rather than bard and lumpy. 

 Adhesion is a surface action, and such a soil will hold more moisture in a time 

 of drouth, will receive more from the air, and will give more to the roots than 

 will one that is baked and hardened. 



CULTIVATION. 



The primary object of cultivation is to stir and pulverize the surface of the 

 soil that has been hardened and packed by the rains. Tiie finer the soil the 

 more surface there is to hold moisture and for the action of roots. In a pul- 

 verized soil the air circulates freely, decomposing its organic matter and freely 

 depositing moisture in the cool soil as it does upon cooler objects above ground. 

 A well cultivated field will seldom suffer from drouth. Waring says that if 

 corn could be hoed every day it would do well with not a drop of rain during 

 its existence. 



