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Knowledge about the interactive effects of N and drought stresses on 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·' soil in the greenhouse and 0, 60, 120, and 180 kg N ha·' 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 aN 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.

A means of quantification of plant root branching, specifically under stress, is of importance for evaluating the contribution of plant roots to water and nutrient uptake and subsequently plant growth. An experiment was conducted to describe the morphology of com (Zea 11Ulys L.) root systems using fractal analysis and also to determine if a root's fractal dimension (D) is altered by N stress. Com genotypes (873 x LH105 and N74 x Mo17) were planted in peg boxes, 1.2 m long, 1.2 m deep, and 0.05 m wide tilled with 20:80 soil to sand mixture and were grown with N rates of 0, 10, 20 and 30 mg kg·•. Thirtynine days after planting, the mixture was gently washed from the roots and the roots were divided into nine sections (squares of side 304.8 mm) and slide photographs were taken from each section. The slides were projected on grids made up of 12 1 , 24 1 , and 48 1 squares of sides (r) 25.4, 12. 7, and 6.35 mm, respectively. Regression of log of number of squares intersected by roots vs. long of r levels was used to determine the slope (-D). Fractal dimension was significantly smaller for zero N compared to applied N with no detectable difference among applied N levels. Fractal dimension was highest for the section directly below the crown (D = 1. 73) indicating high root branching and was lowest for the sections in deeper soil (D = 1.19, average of 3 sections in the 0.6 to 0.9-m depth) indicating less branching. The intercept of the regression line (log K), which indicates root abundance, was lowest for zero N. Amount of roots in the section directly below the crown was 45% of total roots. Nitrogen stress changed the morphology of corn root system and caused less root branching. Fractal analysis was a useful method for describing the morphology of com root systems, both quantitatively and qualitatively.

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