A MODIFIED SOIL MONOLITH TECHNIQUE FOR CHARACTERIZING ROOT SYSTEMS

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.