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Root Morphology and Early Development of Maize at Varying Levels of Nitrogen¹

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 inaeased with increasing N, but the elongation rate of an individual axis did not respond strongly io 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 cotlld accurately represent root length and root initiation as a function of tune and N level.

Key Words: Root length • Root apex • Nitrate • Slant-board

² Former graduate assistant and associate professor of Soil Physics, University Park, PA 16802, and plant physiologist, U. S. Regional Pasture Research Laboratory, AR-SEA-USDA, respectively.

Received for publication September 10, 1979.

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