A soil and root system sampling technique that accurately measures roo
t distribution within the soil profile without causing excessive damag
e to experimental plots would improve the efficiency of root system re
search. A monolith mapping root sampling technique is described that c
ombines the positive attributes of the soil monolith and profile wall
methods with a less destructive hand tool sampling protocol. The objec
tive of this field study was to compare monolith mapping with a standa
rd monolith washing technique for the purpose of measuring root distri
bution in the upper 30 cm of the root zone. Root systems of maize (Zea
mays L.) (V6 stage of development) from plots (Vienna loam soils; fin
e-loamy, mixed Udic Haploborolls) treated with broadcast or banded P w
ere sampled using the modified monolith method. The roots present in t
he soil monolith were mapped (monolith mapping method), and the maps u
sed to represent two-dimensional root distribution. The soil monolith
was then grid-sectioned into 5.1 by 5.1 by 7.6 cm rectangular blocks a
nd washed to separate roots from the soil. Root length was then measur
ed using a line-intersect method (monolith washing method). Monolith m
apping and monolith washing methods both detected differences in root
system distribution in the soil profile. A significant linear relation
ship (r = 0.87) between root length density and root number as measure
d by the two methods allows conversion of the numerical data collected
by the monolith mapping method into root length density values. We co
nclude that monolith mapping works well for determining the spatial di
fferences in root distribution in the upper 30 cm of the root zone. Th
e relative time requirements, accuracy, and less destructive nature of
the technique (compared with the trench profile and framed monolith m
ethods) result in more efficient collection of data on root system cha
racteristics.