MAINTAINING SOIL FERTILITY 2"] 



able crops. The land is usually plowed two or three times, at 

 intervals, or plowed once and harrowed two or three times. 

 This procedure keeps down the weeds and increases the moisture 

 in the soil. According to King, 203 tons more water was found 

 on fallowed land per acre in the spring following the fallow, 

 than on land that was not fallowed, and 179 tons more water 

 was found on the fallowed field after a crop was harvested 

 than on the other field. ^ 



Fallowing increases the supply of available nitrogen as ni- 

 trates and in some sections fallowing is practiced for this reason. 

 The yield of the crop following fallowing is increased but con- 

 siderable humus is lost by being oxidized, and generally more 

 nitrates are formed than can be used up by the crop following 

 fallowing. Snyder has found by experiments that 590 pounds 

 of nitrogen per acre were lost by two years of summer fallow- 

 ing, or an amount sufficient for five wheat crops.- At the Roth- 

 amstead Experiment Station experiments show that considerable 

 more nitrogen was lost from bare soils than from wheat land.* 



On rich soils the losses are greater than on soils deficient 

 in organic matter because the oxidation of humus is more rapid. 

 It is evident, then, that fallowing increases the production of 

 crops at the expense of a reduction of humus. 



In sections of plentiful rainfall, fallowing is often injurious 

 and it should only be practiced in the dry sections where there 

 is not enough rainfall to carry away the nitrates and therefore 

 not sufficient moisture for the continuous growing of crops. 



Other Ways Nitrogen is lost. — The washing away of nitrogen 

 as nitrates is not the only way this element is lost, but con- 

 siderable of this valuable constituent escapes in the form of gases. 

 This loss as gas is occasioned by denitrification, which reduces 

 the nitrates to gases, and the liberation of nitrogen from organic 

 matter. The loss on soils rich in organic matter is greater than 

 on poor soils. 



Experiments show that in continuous cropping more nitrogen 



' Roberts, The Fertility of the Soil 

 -Snyder, Soils and Fertilizers. 



