The present study with young poplar trees aimed at characterizing the effect of O2 shortage in the soil on net uptake of NO3- and NH4+ and the spatial distribution of the N taken up. Moreover, we assessed biomass increment as well as N status of the trees affected by O2 deficiency. For this purpose, an experiment was conducted in which hydroponically grown young poplar trees were exposed to hyp...

Here we report on 3 years (1996-1998) of measurements of organic and inorganic nitrogen (N) fluxes to and from Green Lakes Valley, a high-elevation ecosystem in the Colorado Front Range of the Rocky Mountains. Nitrate-N (NO3-N) was the dominant form of N in both precipitation and stream water. Annual precipitation contained 52% NO3-N, 32% ammonium-N (NH4-N), 9% dissolved organic N (DON), and 7%...

Incubation experiment was conducted on four soil types in Nigeria using cattle dung (CD) at the rate of 2.5g/kg soil ( 5 t ha), Urea fertilizer at the rate of 0.1g/kg soil ( 200 kg ha ) and cattle dung (2.5g/kg soil) combined with Urea 0.05g/kg soil (100 kg ha) as treatments. The objective of the experiment was to compare the rate of OC, NH4 – N, NO3 – N and available P release on soils selecte...

Soil microorganisms can use a wide range of N compounds but are thought to prefer NH4 . Nevertheless, N isotope dilution studies have shown that microbial immobilization of NO3 can be an important process in many soils, particularly relatively undisturbed soils. Our objective was to develop a method for measuring NO3 immobilization potential so that the relative contributions of bacteria and fu...

Whether in response to remotely sensed plant N status or as a rescue treatment when previously applied N has been lost to denitrification or leaching, there is growing interest in applying N to corn at midseason. While the yield benefits of this practice are variable, little information is available as to the impacts of midseason N application on water quality. We compared grain yields and NO3 ...

The relationships between N fertilizer rate, yield, and NO3 leaching need to be quantified to develop soil and crop management practices that are economically and environmentally sustainable. From 1996 through 1999, we measured yield and NO3 loss from a subsurface drained field in central Iowa at three N fertilizer rates: a low (L) rate of 67 kg ha(-1) in 1996 and 57 kg ha(-1) in 1998, a medium...

We investigated the effects of dietary nitrate (NO3 (-)) supplementation on the concentration of plasma nitrite ([NO2 (-)]), oxygen uptake (V̇o2) kinetics, and exercise tolerance in normoxia (N) and hypoxia (H). In a double-blind, crossover study, 12 healthy subjects completed cycle exercise tests, twice in N (20.9% O2) and twice in H (13.1% O2). Subjects ingested either 140 ml/day of NO3 (-)-ri...

Earthworms play an active role in soil nitrogen cycling. Past research has shown that earthworm castings are enriched in NO3 ÿ and NH4 + and show a high potential for microbial nitri®cation and denitri®cation. Little information is available on microbial populations and N transformations in the 1±2 mm thick soil lining of earthworm burrows (the drilosphere). We measured nitrifying bacterial pop...

Most plants use nitrate (NO3-) as their major nitrogen (N) source. The NO3- uptake capacity of a plant is determined by three interdependent factors that are sensitive to NO3- availability: (i) the functional properties of the transporters in roots that contribute to the acquisition of NO3- from the external medium, (ii) the density of functional transporters at the plasma membrane of root cell...