THE INFLUENCE OF IRRIGATION WATER ON 



SOIL FERTILITY 



Irrigation water is applied to a soil primarily to meet the needs 

 of the growing plant. Incidentally, it materially modifies the 

 chemical, physical, and biological properties of the soil, (i) 

 Water may increase or decrease the available plant-food in the 

 soil without changing the total quantity; (2) water may carry 

 from the soil plant- food, thus leaving it intrinsically less fertile; 

 (3) water may carry to a soil phosphorus, potassium, and nitro- 

 gen, therefore increasing its total plant- food; and (4) water 

 may carry to and deposit in a soil alkalis which in time may ren- 

 der it barren. The magnitude of these changes will be deter- 

 mined by the nature of the soil, the composition of the irrigation 

 water, and the intelligence with which each is handled. There- 

 fore, it is interesting and practical to consider briefly such changes 

 as irrigation water may produce on a soil. 



Ammonification. — Water is a universal solvent, as is exempli- 

 fied by the fact that pure water is a chemical curiosity found only 

 in the laboratory where it is obtained with great difficulty and 

 maintained in a state of purity with great care. It is well known 

 that when water becomes charged with carbon dioxid and other 

 acids its solvent powers are greatly increased. It is less well 

 known that the quantity and quality of these solvents which reach 

 a water are governed by the classes and speed with which the 

 bacteria act in the media with which water comes in contact. For 

 bacteria transform the inert atmospheric nitrogen into organic 

 and inorganic compounds. They change the plant residues into 

 ammonia, nitrous, nitric, sulfuric, butyric, carbonic, and many 

 other acids. Bacteria are widely distributed in soil, but like other 

 plants they require water in their metabolism. The speed with 

 which they break down plant debris and transform the nitrogen 



