THK RELATION OF SOILS TO IRRIGATION. 35 



barn-yard manure produces fertilizing results much 

 greater than could be expec5led from the quantity of 

 plant food contained therein. Chemical analysis often 

 discovers quantities of plant food in the soil which 

 seem amply sufficient to produce remunerative crops 

 and yet the soil is pradlically poor. It would thus 

 seem that nitrogen may exist in the soil in an inert 

 form in large quantities and not be available for plant 

 food until subjedl to the decomposing effedls of bac- 

 teria. It has also been found that these ba(5leria mul- 

 tiply and work most acftively quite near the surface of 

 irrigated soil. This accounts for a phenomenon fre- 

 quently experienced in various irrigated distridls. 

 Where it has been necessary to scrape off the surface 

 of the soil in order to make it level enough to irrigate, 

 the land so scraped remains comparatively infertile for 

 a number of years. It is advisable to apply barn-yard 

 manure to irrigated soils by means of a manure 

 spreader so as to break up all large lumps. If these 

 are placed in the dry soil in their entirety they become 

 fang-burned and prove a great detriment to the suc- 

 ceeding crop, and it may require several seasons of 

 excessive irrigation to disintegrate and render them 

 available. To secure best results from manure it must 

 be well incorporated in the soil by plowing under or 

 harrowing in. 



