Influence of the presence of nitrite and nitrate in soil on maize biomass production, nitrogen immobilization and nitrogen recovery

Abstract

When comparing nitrite (NO2 –) and nitrate (NO3 –) toxicity to maize (Zea mays L.) growth, it is important to know the fate of applied nitrogen (N). A pot experiment, using potassium nitrite (K15NO2) and potassium nitrate (K15NO3) was conducted to determine the fate of N (0, 75, 150, and 225 mg N kg–1 soil) applied to a sandy loam soil collected from Gistel (Belgium). The total dry weight of the plants treated with NO2 – was lower than that of the plants treated with NO3 – at 15 and 26 days after N application (harvest 1 and harvest 2, respectively). Shoot and root biomass reduction started at a relatively low NO2 – application rate (75 mg NO2 –-N kg–1). Biomass reduction increased, at both harvests with increasing amounts of NO2 – to more than 55% at the highest application rate (225 mg NO3 –-N kg–1). In the NO3 – treatment, a reduction of 16% in total plant dry biomass was recorded only at the highest application rate (225 mg NO2 –-N kg–1), at both harvest times. The 15N plant uptake (shoots plus roots) at harvest 1 decreased with increasing N application rates of both N forms (KNO2 and KNO3). Twenty-six days after the N application, the total 15N taken up by the plant increased in all treatments in comparison with 15 days after the N application. However, only at higher rates of N application (150 and 225 mg N kg–1) was the 15N uptake by the NO2 – fed plants significantly lower than by the NO3 – fed plants. The percentage of immobilized N from the applied N was low (0–17.7%) at both harvests, irrespective of the N source. However, with relatively low N application rates (75 mg N kg–1), the immobilized N in the soil decreased with time. This may be due to the re-mineralization of the applied N. The percentage of inorganic 15N in the soil in NO2 – treatments was slightly lower than in equivalent doses of NO3 –. This might be due to higher losses of N as N-oxides. Unaccounted for N from the applied N ranged from 21% to 52% for the NO2 – treatments and from 3% to 38% for the NO3 – treatments.