INDEX. 31 



« Page. 



Soil, "gumbo, " depth of moisture, comparison of broken and unbroken soil 13-14 



description 8 



nitrates, causes of decrease 25 



nitrification, effect of plowing 15 



relation of moisture 24-25 



to field factors 18-21 



remarks of L. von Bazarewski 24 



nitrogen content, effect of organic food for nitrifying organisms 24 



virgin and cropped, nitrogen content 25-26 



South Dakota, Bellefourche, inauguration of experiments in dry-land agricul- 

 ture 8 



Spring wheat. See Wheat, spring. 



Stevens, F. L., and Withers, W. A., statement concerning nitrification 22 



Stoddart, W. C, Whitson, A. R., and McLeod, A. F., statement concerning 



nitrogen content of soil 25-26 



Summary of bulletin 27-28 



Summer fallow. See Fallow, summer. 



Thermograph, use in recording air temperature 19 



Traps, G. S., remarks on relation of nitrates in crops to nitrifying activity in 



soil 18 



Vetches, occurrence in sod of experimental plats 9 



Wheat-grass, occurrence in sod of experimental plats 9 



plat, removal of nitrates, comparison with fallow plat 15 



spring, plat, nitrates present, comparison with fallow and corn plats . . . 16-17 



variation 14-16 



Whitson, A. R., Stoddart, W. C, and McLeod, A. F., statement concerning 



nitrogen content of soil 25-26 



Withers, W. A., and Stevens, F. L., statement concerning nitrification 22 



173 



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