Nitrification Period Research Articles

The emission of nitrous oxide upon wetting a rice soil following a dry season fallow

A greenhouse experiment was conducted to measure nitrous oxide (N2O) emissions from a soil, which had been planted to flooded transplanted rice, as it was rewetted to simulate the end of a dry season fallow period. The pots of soil had been cropped to transplanted rice with two commonly used nitrogen (N) fertilizer treatments and a control, and the soil had been puddled before transplanting. Large amounts of nitrate N accumulated in the soils during the dry season fallow, and the N fertilizers applied to the previous crop had little effect on nitrate accumulation. There was little N2O emission during the nitrification period. With water additions meant to simulate rainfall events at the beginning of a wet season, the soil redox dropped slightly, and large amounts of N2O began to be emitted. Large emissions began 5 days after each of the two simulated rainy season watering events and stopped abruptly at soil saturation, even though considerable amounts of nitrate still remained in the soil after saturation. Total measured emissions amounted to 6 to 7 kg N2O‐N ha−1 for the period. Although these measurements were made in a system which may have favored nitrate accumulation, they are the first known measurements of N2O made from a rice soil as it is wetted. Nitrous oxide emitted from the flooding of rice soils that have accumulated nitrate during a dry season fallow may be a major source of N2O additions to the atmosphere.

Experimental examination on nitrous oxide accumulation during nitrification in a freshwater lake.

The N2O production during nitrification was studied in Lake Kizaki by vertical observations and two incubation experiments. The apparent N2O production (ΔN2O), the difference between observed and atmospheric-equilibrium concentration, was highly correlated with apparent oxygen consumption (-ΔO2), in situ NO3- concentration and the amount of NH4+ decrease with time, indicating that N2O was produced by the nitrification process. In a long-term in situ incubation, simultaneous accumulations of NO3- and N2O were observed, the amounts of which were comparable to the in situ changes, suggesting their in situ productions. Both NO3- and N2O productions were greatly enhanced by an NH4+ enrichment after the emergence of nitrification activity. From both vertical observations and long-term in situ incubations, the yield of N2O relative to NO3- production was estimated to be about 0.1% during the active nitrification period. But thereafter, the obtained yields were appreciably higher. Another incubation experiment also showed that N2O production was delayed several days compared to NO3- production, indicating that N2O production was accelerated in the late phase of nitrification. The physiological state of nitrifiers was suggested to be of some importance for such phenomena. Nitrapyrin, a specific inhibitor of nitrification, was found not to be very effective for N2O formations in contrast with NO3- productions completely inhibited, suggesting a possibility of some N2O sources other than autotrophic nitrification.

The fate of labelled15N urea and ammonium nitrate applied to a winter wheat crop

Labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France. Two applications of fertilizer were given: 50 kg N ha−1 at tillering (early March) and 110 kg N ha−1 at the beginning of stem elongation (mid-April). The kinetics of urea hydrolysis, nitrification of ammonium and the disappearance of inorganic nitrogen were followed at frequent intervals. Inorganic nitrogen soon disappeared, mainly immobilized by soil microflora and absorbed by the crop. Net immobilization of fertilizer N occured at a very similar rate for urea and ammonium nitrate. Maximum immobilization (16 kg N ha1) was found at harvest for the first dressing and at anthesis for the second dressing (23 kg N ha1). During the nitrification period, the labelled ammonium pool was immobilized two to three times faster than the labelled nitrate pool. No significant net15N remineralization was found during the growth cycle. The actual denitrification and volatilization losses were probably more important than indicated from calculations made by extrapolation of fluxes measured over short intervals. However microbial immobilization was the most important of the processes which compete with plant uptake for nitrogen.

The Infuence of the Depth of the Secondary Sedimentation Tanks on the Sedimentation Efficiency at Bromma Sewage Treatment Plant

Bromma sewage treatment plant is the second largest plant in Stockholm with a design flow of 160,000 m3/d. The wastewater is treated mechanically, chemically by pre-precipitation with ferrous sulphate, and biologically by the activated sludge process. The requirements for the plant are 8 mg BOD7/l, 0.4 mg P/l and 2 mg NH4+-N/l. The requirement for ammonia refers to the period July-October. In order to meet those rather stringent requirements, the biological step was expanded 3 years ago with 6 new sedimentation tanks. The 6 new tanks have the same area as the 6 old ones but they have only a depth of 3.7 m compared with the depth of the old tanks, 5.7 m. Experience from the first years of operation of the new tanks is that these tanks are more sensitive and less efficient than the older ones. It seems that the effluent suspended solids concentration from the old tanks is less influenced by rapid flow variations than the concentration in the effluent from the new secondary sedimentation tanks. During the nitrification period denitrification takes place to some degree in the secondary sedimentation tanks. This may cause loss of solids and it has been observed that the deeper old tanks usually produce an effluent of better quality and seem to be less influenced by denitrification than the new ones.

Nitrification in Egyptian Soils

An attempt has been made to determine the intensity of the biological processes in the soil during the most important periods of the Egyptian farm rotation. The fluctuations of the nitrate content in the surface soil have been taken as the most important index of this activity.In all cases the moisture content of the soil limited these processes more than any other factor.There was observed throughout the season in a cotton field a relatively large amount of nitrate, more than sufficient for the immediate needs of the cotton plant. The lack of response on the part of the Egyptian cotton crop to nitrogenous fertilisers may be accounted for in part, if not entirely, by the fact that nitrification in the soil is well ahead of the needs of the crop.Nitrification under wheat and maize shows in general the same characteristics in Egypt as in other parts of the world; there is no accumulation of nitrate in the soil.The winter fallow, depending for its water on the rainfall, may be a period of steady nitrification when the amount of the rainfall is sufficiently high.