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.