DRY FARMING CONGRESS. 



18o 



I am going to give you iM-iefly a little experiment carried on by a 

 greenhouse, showing about what happened. Of course in the greenhouse 

 we exaggerate conditions; you get conditions there that you will not get 

 in the field. They are much more extreme than conditions in the field, 

 but they will show a point, I think, moi-e clearly than reference to a field 

 condition. We packed the soil in a number of paraffined wire baskets, 

 so that it was impossible to get any air supply except from the surface, 

 and after one or two crops of clover had been grown on that soil clover 

 refused to grow, and we could not get it to grow, no matter how many 

 times we planted it. Then if we examine that soil we find that the bac- 

 terial contents of the soil has changed. The bacteria now, instead of 

 being as they were in the soil originally, largely of the nitrific type, or 

 the ones that change the materials into food which the plant can uise 

 to denitrific bacteria, wdiich change the foods into things the plant cannot 

 use. Then if we take this bad soil, as it now is, and dry it, pulverize it, 

 stir it up, several ways we can manipulate it to change the conditions to 

 some extent, let that stand a while to let the desired bacteria liegin grow- 

 ing again, then we can grow clover in that soil again. This will show you, 

 and in a very exaggerated way, what may happen if you get the wrong 

 kind of cultural conditions in a field. I don't say we can tell you every 

 time. No bacteriologist could go into a field at this stage of the investi- 

 gations and say when conditions were favorable and when the}^ were not. 

 But we are gradually w^orking towards that end. 



There is another experiment that I want to give you very briefly 

 that will show you a different kind of condition. 



Ground that was to be planted to alfalfa was seeded on one-half of 

 a field with seed inoculated with a pure culture of nitrific organism. You 

 must have a nodule-forming organism in the soil before alfalfa will grow, 

 or before it will grow and produce a satisfactory crop. On the half that 

 was not inoculated with the pure culture we used soil from an old and 

 productive alfalfa field. I should explain that this soil, we are experi- 

 menting on is soil thoroughly cleared, and has been burned over. It was 

 scrub oak soil. When this alfalfa crop grew, only half of it grew — the 

 half that had been inoculated with soil. On examining bacteriologically 

 the samples of the soil from the two halves of that field we found that 

 the soil that had been inoculated with the old field soil had all the proper 

 bacteria present, or, at least, judging from our present study of the bac- 

 teriological investigations, a great many at least of the necessary bacteria 

 were present. The other half of the field showed a great many bacteria 

 of the undesirable type, and none of the type that finally changes things 

 into the plant food that is necessary. Evidently the bacteria that were 

 necessary "in this case had been brought in with that old soil from the 

 old field. 



This is not a case, however, of nodule formation. Sometimes in a 

 field nodule-forming bacteria are lacking, as I told you a moment ago, but 

 nodule-forming bacteria were present in both halves of this field, and it 

 was merely the lack of that special type of organism, at least that seems 



