Organization of root growth information for maize (Zea mays L.) indicated a lack of data on the N response of make roots. Thus, the objective of this study was to quantify the morphological response of maize roots to N.
Growth chamber and field studies were conducted. Field‐grown maize was sampled during the 4 weeks after emergence to evaluate differences between field and growth chamber data. Numbers of seminal roots and lengths of the seminal root system did not increase substantially after 8 days. The nodal root system increased exponentially from 1.6 m at 8 days after emergence to 21 m at 29 days after emergence. Using the slant‐board culture technique, maize plants grown in a growth chamber received 0, 21, 42, 105, or 210 ppm total N from 50% Noagland solutions. Six plants of each treatment were harvested at 3, 10, or 17 days after emergence. Total root length of maize grown at the highest N level increased exponentially from 1.7 m at 3 days after emergence to 148 m at 17 days after emergence. Root apices increased from 111 to greater than 2,900 during the same period. Primary root (axis) numbers per plant increased with increasing N, but the elongation rate of an individual axis did not respond strongly to increased N. Frequency of laterals increased slightly as N was increased, but first order lateral elongation rate increased more strongly with increasing N. Response of shoot dry weight, root dry weight, shoot to root ratios, and leaf area to N paralleled the morphological response of roots to N. It was concluded that a growth equation which incorporates a function similar to a Michaelis‐Menten equation could accurately represent root length and root initiation as a function of time and N level.
Two experiments were conducted on an undisturbed Hublersburg silt loam (Typic Hapludult) soil to evaluate two different soil solution sampling techniques. The two techniques were employed simultaneously to sample the leachate at depths of 38 to 120 cm when water was added at the soil surface with known concentrations of NO3‐N (0‐579 ppm) and Cd2+ (0.0001–5.45 ppm). After each controlled water addition to the surface, soil water samples were taken for analysis with porous cup soil water samplers and with devices located in a subsurface horizontal tunnel.
Large differences in ion concentration occurred between data obtained from the soil water samplers and from the horizontal tunnel. Calculations based on water retention data indicated that in excess of 90% of the total flow occurred in pores drained by water potentials of 0 to −20 cm of water. This pore class is considered to be dominated by interped cracks and to cause a channeling of solution past the porous cup samplers. It was concluded that under wet soil conditions, soil water samplers are not suitable for monitoring the chemical quality of the water percolating through the soil profile.
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