Abstract: The effect of nitrate nutrition and long-term waterlogging on the pattern of accumulation of inorganic nutrients in different plant organs was studied in corn (Zea mays L.) in glasshouse conditions. Continuous flooding of soils with NO3 added for 21 days, caused a complete depletion of NO3, but in turn NH4-N increased significantly in these soils. Potassium (K) and phosphorus (P) contents in the flooded soils also increased whereas calcium (Ca) and magnesium (Mg) contents remained unaffected. Iron (Fe) and manganese (Mn) contents increased manifold as a result of flooding. Long-term flooding caused a marked reduction in dry weight of both shoots and roots, and supplementary NO3-N exacerbated the inhibitory effect of waterlogging on plant growth. A considerable decrease in nitrogen (N), P, and K contents in leaves was observed as a result of flooding, whereas in roots the reverse was true. However, N and P contents under waterlogged conditions increased consistently with an increase in the applied NO3 level. Flooding caused a marked reduction in Ca in both leaves and roots, and Mg only in leaves. Enhanced soil NO3-N had no effect on the concentration of Ca and Mg in leaves or roots. Concentrations of Fe and Mn in leaves and roots increased significantly due to continuous flooding, but a marked increase in these two nutrients was observed in roots. Addition of NO3-N to the waterlogged soils caused a slight increase in Fe in both leaves and roots but did not affect the Mn content in leaves or roots. Supplementary NO3-N was inhibitory to corn growth under long-term hypoxic conditions, particularly, the two higher concentrations (294 and 392 mg NO3-N kg-1 soil).

Abstract: The interactive effect of additional amount of NO3-N and long-term waterlogging on maize was studied in glasshouse conditions. Forty-two-day- old plants were subjected to continuous flooding for 21 days at three different NO3-N regimes (196, 294 and 392 mg N kg-1 soil). Shoot fresh mass and leaf area of waterlogged plants reduced significantly at two higher NO3 regimes. Leaf water potential was generally decreased, whereas osmotic potential increased in all waterlogged plants but much reduction in leaf water potential was found at the highest external NO3 regime. Leaf turgor potential decreased due to waterlogging but this decrease progressed with increase in external NO3 concentration. Chlorophylls 'a' and 'b' increased in non-waterlogged plants with increase in NO3 concentration of the growth medium, but these two pigments decreased significantly due to waterlogging particularly at the two higher NO3 regimes. Chlorophyll a/b ratio increased linearly in non-waterlogged plants with increase in external NO3 regimes but the ratio remained almost unchanged due to waterlogging. Waterlogging caused a reduction in net photosynthesis and stomatal conductance but no effect of additional amount of NO3 was observed on these two variables. Transpiration was also decreased as a result of waterlogging but a marked reduction in this variable was observed at the highest external NO3 concentration. Water-use efficiency increased with increase in external NO3 concentration in both waterlogged and non-waterlogged plants. Although waterlogging caused a reduction in substomatal CO2 concentration, it generally increased in both waterlogged and non-waterlogged plants due to supplementary NO3, particularly at its highest concentration. From these results, it is clear that supplementary NO3 in the growth medium of maize plants experiencing long-term waterlogging had injurious effect on growth.