ROOT DEVELOPMENT AND NITROGEN INFLUX OF CORN GENOTYPES GROWN UNDER COMBINED DROUGHT AND NITROGEN STRESSES

Knowledge about the interactive effect, of N and drought stresses OH corn (Zea mays L.) root morphology and rate of N uptake is important for selecting drought tolerant and/or N efficient genotypes and for determining mechanisms that control root growth under stress. The objective was to study these interactions by growing three and four genotypes of known N utilization efficiency (NUE, kg grain/kg N uptake) responses in greenhouse and field experiments, respectively. Nitrogen application rates were 0, 30, 60, and 90 mg N kg-1 soil in the greenhouse and 0, 60, 120, and 180 kg N ha-1 in the field experiment. Water regimes included nonstress vs. an 8-d water stress in the greenhouse experiment and dryland vs. irrigation in the field. Water-regime-by-N-rate interactions were not significant for root dry weight, length, average radius, root/shoot ratio, and N influx in either environment. Root weight and length were different among genotypes. The genotype with the greatest amount of roots deep in the soil had the highest grain yield increase with irrigation. Root mass and root length were greater, but mean N influx was two to three times smaller in the zero N treatment than in the applied N treatments (average of all genotypes). Severe water stress reduced corn root mass and length in the greenhouse. Moderate water stress in the field, however, significantly increased root length. Water use efficiency was positively correlated with root mass and length in the greenhouse. Water regime did not affect N influx in either experiment. These results showed that corn response to irrigation will be altered depending on root morphology, and that insofar as possible, the root system should be considered when selecting for N efficient and/or drought tolerant corn genotypes.