Date of this Version
Thesis (M.S.)--University of Nebraska--Lincoln, 1946. Department of Agronomy.
Observations made during the past several years indicate that many Nebraska soils are deficient in available nitrogen. During the growing season of 1945, nitrate production was studied in soils growing corn where different cropping and cultural practices were followed. The specific objectives of the study are as follows: (1) to compare the nitrification rates of soil samples air-dried prior to incubation with the nitrification rates of soil samples incubated without air-drying as measurers of the capacity of field soils to produce nitrate-nitrogen throughout the season; (2) to determine the influence of cropping and cultural practices upon the seasonal trend in nitrification rates of soils growing corn; and (3) to determine the relationship between nitrification rates of soils and the yields of corn grown on those soils.
A high degree of correlation was obtained between the nitrification rates of soil samples air-dried prior to incubation, indicating that either method of pretreatment is as satisfactory as the other method. A highly significant correlation was obtained between the nitrification rate at the eight-week incubation period. Highly significant differences in nitrification rates for cropping and cultural practices, for sampling time and for length of incubation period were obtained for the three sets of plots studied at Lincoln. A highly significant difference for incubation period and significant differences for cropping and cultural practices and for sampling time were obtained for the fertility plots at Holdrege. Nitrification rates were higher early in the season and decreased gradually as the season progressed regardless of the cropping and cultural practices followed.
Nitrification rates were considerably higher in the soils where a legume crop has been grown or manure had been applied than in soils where no legume had been grown or manure had been applied. Relatively similar nitrification rates were obtained in soils where corn followed different grasses as were obtained in soils where corn followed immediately after a legume. Nitrification rates of soils growing corn where different methods of residue disposal were followed were of the same magnitude throughout the season. Nirtification rates of either subtilled or plowed plots were significantly higher where a legume crop had been grown than where no legume crop had been grown. Nitrification rates of soils and yield of corn grown on those soils were positively but not significantly correlated.
Advisor: H. F. Rhoades.