EFFECT OF NITROGEN FORM ON MAIZE RESPONSE TO DROUGHT STRESS

Two hybrids of maize (Zea mays L.) differing in resistance to drought, were grown in chernozem soil in a greenhouse and were fertilized with two different forms of nitrogen: Ca(NO3)2 and (NH4)2SO4 in concentrations corresponding to 100 kg of N ha-1. After emergence of the 4th leaf, plants were exposed to drought. During the drought period, the parameters of plant water status (water potential, osmotic potential, turgor pressure and relative water content) and chlorophyll a + b concentration were monitored every two days. N and K concentration and accumulation over the drought period were also monitored. Next to differences in adaptability of the two hybrids to drought, the results demonstrate different adaptability of NH4 and NO3-treated plants within each hybrid. NH4-plants of each hybrid maintain higher turgor pressure during the drought by better osmotic adaptation. Especially significant differences appear between chlorophyll (a + b) values of NH4 and NO3-treated plants and as affected by drought. Chlorophyll concentrations of NH4-plants are higher than those of NO3-plants both in control and droughted plants. NH4 plants show a characteristic initial chlorophyll increase at the beginning of the drought period while in NO3 plants chlorophyll constantly decreases throughout the whole drought period. The influence of the nitrogen form on chlorophyll concentration changes during drought does not appear to be affected by regulation of the K concentration.