228 Bulletin 247. 



chemical elements unless these elements exist in a form available to the 

 plants at the proper time and place. 



There is no doubt, either, that injurious substances, such as alkali, 

 may prevent the growth of plants, nor that certain substances, such as 

 lime, may be injurious to some plants while highly beneficial to others. 

 The question is not whether the various factors are important : in fact 

 they are all essential ; but what influence do approved agricultural meth- 

 ods have in modifying these factors and thus increasing the yield of 

 crops? Of two farmers one raising 40 bushels of maize, and another by 

 different cultural methods which we call superior because of the results, 

 producing 60 bushels, the question is which of these essential factors 

 has he modified? Of two pieces of land cultivated precisely alike one 

 produces 40 and the other 60 bushels. What is the cause? Has the 

 light, heat, moisture or plant-food been different? Or have fungous dis- 

 eases, insect enemies or injurious chemicals in the soil been the determi- 

 ning factor in the yield? Or is it a combination of many factors? 

 And if so, by what rational method may we hope to modify these factors 

 so as to increase the yield? Why do the states of the Mississippi Valley 

 produce over 30 bushels of maize per acre and the South Atlantic States 

 less than 15 bushels per acre? Is it light, heat, moisture, plant- food or 

 toxic substance? Who will venture an answer? 



There was a time in so-called scientific agriculture when all prac- 

 tices were based on the theory that the various cultural methods modi- 

 fied the quantity of plant-food, the amount of which could be mathe- 

 matically determined. Then followed a period in which the conservation 

 of soil moisture was insisted on as the important factor in crop growth 

 and farmers were advised to modify their cultural methods accordingly. 

 Now comes the doctrine of soil sanitation ; that soil may become unhealthy 

 for the successful growth of crops and that our aim must be to so manip- 

 ulate and dose our soil as to make it healthy. It is perhaps not without 

 some significance in this connection that for 2,000 years the value of the 

 rotation of crops has been recognized, while some of the reasons stated 

 for its beneficial influence, even in the most modern discussion of the 

 subject, would hardly bear critical analysis. I may say by way of 

 parenthesis that notwithstanding the advice given to farmers during the 

 past 75 years, they still continue to grow crops. I think I may say 

 without fear of contradiction that there never was a time in the United 

 States when so much agricultural product was produced per unit of 

 labor as at the present moment. 



The conservation of moisture. 



The writer confesses to have taken part in the propaganda concern- 

 ing the conservation of soil moisture. At least 15 years ago he conducted 



