Nitrogen Behavior and Uptake by Corn as Affected by Time of Application, Nitrapyrin, and Supplemental Winter Heat

130 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.Climatic conditions between the time of fertilizer N application and corn (Zea mays L.) flowering, along with the presence or absence of chemical nitrification inhibitors such as nitrapyrin, largely determine the amount of N lost from the soil. Field studies were conducted at Urbana, Illinois, to evaluate the effects of supplemental winter heat and nitrapyrin applied with fall and spring applications of aqua ammonia on nitrification, nitrapyrin degradation, corn yield, and N uptake by corn. Heat treatments consisted of 29 days at 21 C and 90 days at 10 C in the winter of 1977-1978, and 55 days at 15 C in the winter 1978-1979. Nitrogen rates ranged from 0 to 252 kg/ha and 0 to 336 kg/ha in 1977-1978 and 1978-1979, respectively. Nitrapyrin was applied only in 1978-1979 and ranged from 0 to 1.12 kg/ha. Laboratory studies were also conducted to relate a degree day term (nitrification degree day) to the percent of applied ammonium remaining in the soil at any given time after N application in the presence or absence of nitrapyrin. Nitrogen (0, 341, and 682 ppm) and nitrapyrin (0, 1.7, and 3.4 ppm) were applied to the soil and incubated in temperature controlled chambers for 150 days at 4, 10, 15, and 21 C. At various times during the experiment, the soil was analyzed for ammonium, and the results were compared to field data.Winter soil heating greatly increased nitrification, and at the higher N rates, ammonium was almost completely nitrified by the following spring. Nitrapyrin additions retarded nitrification and as the rate of nitrapyrin increased, nitrification decreased. The response to nitrapyrin was greater in the heated plots. However, the amount of nitrapyrin recovered from the application zone was much lower in the heated plots.Winter heating of plots receiving fall-N decreased grain, stover, and dry matter yields as well as N concentration in the leaf, stover, and grain. The effect of heating the fall-n plots in 1977-1978 was greater than in 1978-1979, but the intensity of heating was also greater in 1977-1978. In the unheated plots, no sizeable differences between fall- and spring-N existed with any plant variable. The efficiency of applied N (increase in plant N uptake per unit of applied N) decreased with increasing N rate. When heat was added after N application, the efficiency of fall-applied N fertilizers decreased.When nitrapyrin was added with fall-applied N, decreases in corn yield and plant N due to heat were partially overcome. However, nitrapyrin additions did not consistently remove the entire effect of heat. When compared to fall-N, spring-N applications to the unheated plots resulted in a higher percent N in the stover and a slightly higher N efficiency at the lower N rates. No other differences existed due to season of application in the unheated treatments. In the unheated, fall-N plots, nitrapyrin additions increased the percent N in the leaf, grain, and stover but decreased grain, stover, and total dry matter yield.In the laboratory study, appreciable amounts of nitrification occurred at 4 C. As the temperature increased, nitrification increased. Nitrapyrin additions greatly reduced nitrification, but the effectiveness decreased with time. At the 0 nitrapyrin level, the values of percent of applied ammonium remaining predicted by nitrification degree days were in close agreement with those values found using field data. However, when nitrapyrin was used, the amount of nitrification predicted from the temperature controlled data was much lower than the actual field values.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD