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Estimating Root Mass in Maize Using a Portable Capacitance Meter

CIMMYT, Lisboa 27, Apdo. Postal 6-641,06600 México D.F., Mexico
Dep. of Plant Breeding, USDA-ARS, Cornell Univ., Ithaca, NY 14853
USDA-ARS, Cornell Univ., Ithaca, NY 14853

^* Corresponding author (jvanbeem{at}cimmyt.mx)

Time and expense are major constraints limiting the detection of genotypic differences in the length, structure, and growth rate of root systems in the soil. Recent development of a hand-held capacitance meter could enable the routine quantification of root mass. The objective of this study was to determine the accuracy with which a BK Precision 810A capacitance meter can estimate root fresh mass in maize (Zea mays L.) using a technique that allows a rapid and noninvasive capacitance reading. The capacitance meter measured root capacitance of maize grown under greenhouse (8 genotypes) and field (6 genotypes) conditions. After the capacitance readings, 14 plants per genotype were uprooted, roots were washed thoroughly, and root fresh mass was obtained. The statistical relationship between capacitance and root fresh mass in greenhouse experiments was significant early in the growth season for all genotypes (r² = 0.73, P < 0.001), and significant only late in the growth season for inbreds (r² = 0.56, P < 0.001). Field studies showed that capacitance and root fresh mass were statistically correlated for all genotypes at flowering (r² = 0.69, P < 0.001). In conclusion, capacitance meters equipped with a clamp for rapid attachment to the plant may facilitate the nondestructive identification of genotypes with root characteristics that confer adaptation to various environments. Conditions for accurate capacitance measurements included a moist medium around the plant's root system and a consistent placement of the electrode at 6 cm above the crown.

Received for publication January 27, 1997.