322 



SOIL PHYSICS AND MANAGEMENT 



sunlight does not penetrate to it. All inoculating material and 

 inoculated seed should be kept from direct sunlight, because of its 

 drying effect. 



Loss of Nitrates. Soils lose nitrates in three ways: by leach- 

 ing, denitrification and by the growth of weeds or other plants 

 foreign to the crop. 



1. Leaching. The greatest loss of nitrates is through leach- 

 ing. Nitrates are very readily soluble in water. During rains those 

 formed in manure heaps or soil may he carried into drainage sys- 

 tems and lost. That this does occur to a considerable extent is 

 shown by analysis of drainage waters. 



Deherain collected drainage waters from cement tanks with 

 results as given in the following table. The tanks had been filled 

 several years before. 



Loss of Nitrates by Leaching 6 



The rainfall during the season was 28.8 inches. It is very inter- 

 esting to note the effect of the crop on the amount of drainage and 

 also on the nitrogen removed with the water. Catch crops are of 

 value in preventing loss of nitrogen in this way. Even weeds may 

 serve as a catch crop after the main crop is removed. 



Fallowing (leaving land without a crop and cultivating during 

 summer) in humid areas is a very expensive operation and should 

 never be practiced. It will not be necessary if the organic matter is 

 properly maintained. Fallowing is resorted to when the active 

 organic matter has been largely removed by cropping and some 

 special means must be taken to render the less active form avail- 

 able. This is accompanied with too much loss of the most expen- 

 sive plant food, nitrates in soils, to be profitable. In the above table 



