ESTIMATING ROOT MASS IN MAIZE USING A PORTABLE CAPACITANCE METER

Time and expense are major constraints limiting the detection of genot ypic differences in the length, structure, and growth rate of root sys tems 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 81 0A capacitance meter can estimate root fresh mass in maize (Zea mays L .) using a technique that allows a rapid and noninvasive capacitance r eading. The capacitance meter measured root capacitance of maize grown under greenhouse (8 genotypes) and field (6 genotypes) conditions, Af ter the capacitance readings, 14 plants per genotype were uprooted, ro ots mere washed thoroughly, and root fresh mass was obtained. The stat istical relationship between capacitance and root fresh mass in greenh ouse experiments was significant early in the growth season for all ge notypes (r(2) = 0.73, P < 0.001), and significant only late in the gro wth season fur inbreds (r(2) = 0.56, P < 0.001), Field studies showed that capacitance and root fresh mass were statistically correlated for all genotypes at flowering (r(2) = 0.69, P < 0.001), In conclusion, c apacitance meters equipped with a clamp for rapid attachment to the pl ant may facilitate the nondestructive identification of genotypes with root characteristics that confer adaptation to various environments. Conditions for accurate capacitance measurements included a moist medi um around the plant's root system and a consistent placement of the el ectrode at 6 cm above the crown.